General Knowledge, CPUs, and Safety

General Knowledge, CPUs, and Safety
Unit 1 General Knowledge, CPUs, and Safety Before we dive into how a PC works, let’s have a history lesson. First, we will discuss the history of personal computers.

Charles Babbage’s Analytical Engine
Charles Babbage invented the first mechanical “computer,” but the technology didn’t exist at the time to actually build the machine. Portions of it were built, a single section is shown here. Had he been able to build the machine in its entirety, it would have been a tremendous accomplishment. As it turned out, the system he designed would have worked, as some engineers recently proved when one of his machines was completed.

The Hollerith Machine Dr. Herman Hollerith built the first processing machine in order to accommodate the 1890 census. This machine used punched cards, not unlike those used until the late 70’s. Hollerith’s company eventually changed its name to International Business Machines…

First Electronic Digital Computer
The first electronic digital computer was at Iowa State University, between 1939 and 1942 and was led by John Atanasoff and a graduate student. This machine had many firsts, including binary arithmetic, parallel processing, regenerative memory, separate memory and computer functions, just to mention a few. When completed, it weighed 750 pounds and could store a whopping 3,000 bytes of data. Called the ABC (Atanasoff – Berry Computer), it was partially disassembled to make room for other projects when John Atanasoff went to the Navy during World War II. The technology developed for the ABC machine was passed from Atanasoff to John W. Mauchly, who is responsible for the first large-scale digital electronic computer. The photo shown here is a working reproduction. First Electronic Digital Computer

The ENIAC was the first electronic digital computer
The ENIAC was the first electronic digital computer. It was a huge machine, difficult to use, but it was able to solve mammoth mathematical calculations. The U.S. military used ENIAC to solve missile trajectories. Legend has it that once a bug was stuck in a relay, causing the machine to malfunction. This was, by most accounts, the first use of the word “bug” to describe a computer problem. ENIAC

Around the same time, British engineers developed the Colossus I, another digital electronic computer. Again using vacuum tubes, this machine was instrumental in breaking the German code system in use during World War II. Colossus

Prior to the Personal Computer
Computers were very large. Computers were very expensive. Computers were quite rare. Prior to the personal computer, computers were very large and extremely expensive. Because of their cost, they were also quite rare. You were lucky if you had one in your town, much less your desk. The idea that you might one day have one for your own personal use was absurd.

History of the PC Before the IBM PC - 1975 to 1981 The IBM PC - 1981
The IBM XT The IBM AT The IBM PS/ Waning of IBM as the pace setter to present Prior to the personal computer, IBM dominated the business computing world. Even though IBM was late to the personal computer market, it still set and maintained the personal computing standard for several years. In fact, the history of the personal computer can be subdivided by IBM’s entries into this market.

The First PC Generally considered the MITS Altair
Introduced in January 1975 Based on the 8080 Intel Processor Sold for $395 in kit form The first personal computer arrived on the scene in January of Based on the 8080 microprocessor, it was introduced in build-it-yourself form by a small calculator company named MITS in Albuquerque, New Mexico. It sold for $395 and was called Altair.

Before the IBM PC, personal computers used:
A variety of microprocessors Many different architectures A variety of operating systems Dozens of personal computers from a dozen different manufacturers quickly followed the Altair. The problem was that each of the different manufacturers went their own way, using a variety of microprocessors, operating systems, and architectures. An industry standard was needed before this new technology would be widely accepted.

The IBM PC Introduced on August 12, 1981
Used the Intel 8088 microprocessor Operated at 4.77 MHz No hard drive One or two single-sided floppy drives Used MS-DOS 1.0 Introduced the 8-bit ISA bus In 1981, IBM introduced its first true personal computer, called simply, the IBM PC. It was based on the Intel 8088 microprocessor and operated at only 4.77MHz. It had no hard drive and everything had to be loaded from a floppy disk. Its operating system (MS-DOS 1.0) was from a fledgling software company called Microsoft. While it seems very crude compared to today’s machines, the IBM PC introduced standards into a market that sorely needed them.

The IBM PC brought standardization
Intel Microprocessors Microsoft Disk Operating System (MS-DOS) Architecture At that early stage of the personal computer’s history, IBM had the clout to set standards that would continue for years to come. These included using microprocessors from Intel, operating systems from Microsoft, and design elements whose remnants still exist in today’s PCs.

The IBM XT Introduced in 1983 Included a 10 MB hard drive
Used MS-DOS 2.0 16-bit ISA Bus In 1983, IBM introduced a second design called the IBM XT, for eXtended Technology. The extensions included a 10-MB hard drive, the 16-bit ISA bus, and the software operating system (MS-DOS 2.0) to support it all.

The IBM AT Introduced in 1984 Based on Intel’s 80286 microprocessor
Operated at 6 MHz 20 MB hard drive Used MS-DOS 3.0 In 1984, IBM struck again, this time with the IBM AT, for Advanced Technology. It was the first personal computer to use the microprocessor from Intel. It operated at 6 MHz and used MS-DOS 3.0. But by now, the rest of the world was figuring out how to make computers that were compatible with the IBM standards. A flood of IBM-compatible computers began to appear, taking valuable market share away from the very company that had set the standards.

The IBM PS/2 Introduced in 1988 IBM abandoned its own standard
Microchannel replaces the ISA bus Introduced the VGA graphics standard New OS called OS/2 is DOS compatible, allows multitasking. IBM responded by changing the standards. In 1987, IBM abandoned its own standards in favor of a brand new design called the PS/2. The industry standard architecture (ISA) bus was abandoned in favor of a new bus called the Microchannel. The new operating system called OS/2 was MS-DOS compatible, but allowed multitasking. This time, IBM took no chances. Through patents and copyrights, IBM made it very difficult for other companies to make PS/2 clones. But, by now, it was too late. The era of IBM dominance was coming to an end.

From 1981 to 1987 IBM dominated the personal computer business
IBM set the standards for: Microprocessor used Bus structure Architecture Video Disk Drives etc. From the introduction of the IBM PC to the PS/2, IBM completely dominated the personal computer business. It set the standard for everything from the type of microprocessor used to the way letters were formed on the monitor screen. When it abandoned these standards, the world did not follow.

From 1987 to Present IBM’s influence gradually waned
Software standards set, largely, by Microsoft MS-DOS Windows 3.xx Windows 95, 98, Me Windows NT, 2000, XP Hardware standards set, largely, by Intel Microprocessor, Chipset, Motherboard So from about 1987 until the present, IBM’s influence over the direction of the personal computer has gradually waned. Today, the software standards are set, largely, by Microsoft through it various Windows programs. In much the same way, Intel sets the hardware standards, through the design of its microprocessors, chipsets, and motherboards.

The Language of a Computer

The Telegraph Samuel F.B. Morse 1838 A • – B – ••• C – • – • D – ••
Possibly the first electric communication technology was the telegraph. Early versions used a wire for each letter, making communications over long distances difficult and truly impossible. In 1838 Samuel F.B. Morse developed a code that allowed messages to be sent across a single wire. The code is a series of short and long tones, or dots and dashes. The telegraph had an impact on communications not seen again until the telephone then the Internet; it was truly a revolution.

Analog vs. Digital Analog Signals vary over a continuous range
Digital signals vary between two fixed levels The telegraph was clearly a serial device, but more importantly it was a digital device. Let’s make sure we all understand the distinction between analog signals and digital signals. By definition, an analog signal is continuously and infinitely variable between some values. In contrast, a digital signal is defined as being one of two fixed values.

continuously variable
Analog vs. Digital Analog Signals are continuously variable As a simple example, let’s use a dimmer switch as an analogy. A dimmer can set a lamp to any value between off and fully lit. In this example, the lamp is lit dimly.

continuously variable
Analog vs. Digital Analog Signals are continuously variable In this example, the lamp is lit more brightly, but not completely. Notice that the dimmer switch can still be turned up higher; it is only at the 3:00 position. An analog dimmer switch can control the lamp’s brightness at any level between off and fully lit.

Analog vs. Digital Digital Signals have two levels; on or off
A typical light switch is a good example of the same circuit used in a digital fashion. In this case, the light is in one of its two possible positions, off.

Analog vs. Digital Digital Signals have two levels; on or off
And the other position is fully on. The key is that there is no “in-between.” The light is either on or off. In the same manner, digital signals are either on or off.

Parallel vs. Serial Another very important concept is the difference between a parallel data path and a serial data path. In a serial data path, just one piece of information is sent at a time. This is very much like the telegraph, or the tones you hear from your modem as you connect to the Internet. In a parallel data path, many pieces of information are sent at the same time. This requires several data paths, when talking about computers we a referring to multiple wires. In most cases a parallel data path is expected to be faster than a serial data path. However, engineers have discovered that they can send serial data at rates far exceeding the benefits gained by a parallel data path. Additionally, these serial data paths can extend tremendous distances.

Decimal Numbers 0,1,2,3,4,5,6,7,8,9 called a “base 10” system
Let’s take a look at three major numbering systems. First is the decimal system, which should require no explanation. You have been using this system since you started school, and you know it well. It uses only 10 digits, and as a result is called a Base 10 system. Each digit has a maximum value of nine, then you add another digit.

Binary Either 0 or 1 Requires more digits than decimal for a given value Bit: single digit Byte: eight bits together Word: multiple bytes together In the binary system, each digit has a maximum value of one. Then you add another digit. In the binary system, 10 is equal to two, where in the decimal system 10 is equal to ten. The term “bit” refers to one single binary digit. For instance, a 32-bit CPU can handle 32 binary numbers simultaneously. The term “byte” refers to eight bits. For example, a 32-bit binary number has four bytes. The term “word” could refer to the entire set of 32-bits. This term is primarily used by programmers to refer to the internal workings of a processor.

Binary You can learn the basics of binary numbers the same way you learned about place values with decimal numbers. Whereas each place value in the decimal numbering system is a power of ten, in the binary system each place value is a power of two.

Hexadecimal 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F Called a “base 16” numbering system Requires fewer digits than decimal for a given value Primarily used to make binary easier The hex numbering system is a base 16 system where the highest place value is equal to fifteen. A single hex digit can represent two complete 8-bit bytes, making this system perfect for use in computing systems. The part that is confusing about this system is its use of letters. On the other hand, when you see a letter, always between A and F, you know that the number is hex. Note that a hex number does not require a letter to hold a place value, which is why you might see a hex number with a subscript 16 at the end, or commonly the letter H at the end.

This chart shows you how the three major numbering systems can be compared.

bits nibbles C 2 A B 2 F 5 9 This slide demonstrates how a binary number can easily be converted to hex. If you work with microprocessors or other digital circuits, you soon memorize the basic binary values as their hex equivalents. For instance, 1011 is always B, or decimal 11. As you can see, it is much easier to work with “C2AB” than the binary equivalent of the same value. If you wish to play with these number systems more, the Windows 95/98 calculator can convert them directly in scientific mode. 2F59 bytes C2AB

Identifying Numbers 330H is Hex 3F8 is Hex 256 is Decimal
1010 is Binary Identifying which numbering system is being used is often important. There are clues, but most properly a document should state what system is always used. menu

American Standard Code for Information Interchange (ASCII)
ASCII is a special set of codes that have become the basis of most computer communication. This chart represents the basic ASCII characters, an extended character set includes 255 ASCII characters.

The Computer Bus

CPU Memory Video Adapter Parallel Port Keyboard Controller
This diagram represents an over- simplified computer bus. In order for all the devices on the motherboard to communicate, a special set of wires are connected to many of them. Other devices are connected through other buses, but the idea is that they all use the same pathway. Except, they always take turns using this pathway. The mechanics of how the bus works are not important now. What is important is that you understand what a bus is, and what it does. Also, the number of wires that make up the bus is important, too. Here we are showing an 8-bit bus, so-called because it has eight wires and can handle eight bits at a time. The Data Bus System Controller

CPU Memory Video Adapter Keyboard Controller System Controller
In this example, we have a 16-bit bus, and most of the attached devices have connections to each wire on the bus. Some devices do not need connections to every part of the bus, such as the keyboard. Why? Because the keyboard simply doesn’t need 16-bits to communicate with the CPU. System Controller

CPU Memory Video Adapter
Here we have a 32-bit bus, which we’ve had to simplify just to fit it onto the screen. Again, this is over-simplified, but you get from this an idea of how complex a bus becomes as it increases in size.

CPU Socket (Slot 1) Bus Wires System Controller
This photo show a small part of a real bus. Many of the wires are on the bottom of the circuit board, some even travel through the middle of the board. At the top is the CPU socket, and at the lower-right is the system controller. The bus shown serves ans the communication path between the two devices. System Controller

Computer Components [Note to Instructor: The lab designed to follow Lesson 5: Computer Components, deals with opening the cover of the PC. As you are aware, we must always take precautions against electrostatic discharge (ESD) when working around computers. This presentation deals with ESD and protecting the computer from ESD’s effects.]

The Ultimate Processing Components
Let’s look at a few examples of Processing Components, or devices who’s main job is to process data. The main device, obviously, is the processor.

ATX Motherboard The motherboard is a processing component, although it exact role fits across all three categories.

Processing Components
There are others as well. Starting up on the left and moving clockwise, there are expansion slots. The bus is also a vital processing component. Batteries and clocks keep all the circuits in time, and below that is the chipset. And of course, memory is always storing data that is being processed.

Input Devices Keyboards Scanner Mice Microphone Trackballs CD-ROM
J-mice Biometric Scanner Scanner Microphone CD-ROM Touchpads Input devices are defined as anything you used to control the computer. Touchpads and j-mice are normally used with notebook or laptop computers. Game controllers include all manner of devices, including joysticks. Keyboards and mice typically attach to the system through dedicated interfaces, usually clearly labeled on the rear of the computer.

Output Devices Monitors Printers Speakers
Inkjet, Laser, Dot-matrix, Plotters Speakers Most of these are fairly obvious output devices. Any device that converts data into a format for a human to see, hear, or feel information is an output device. Menu

Input/Output Devices Floppy Drive Hard Drive Modem
Network Interface Card CD-R/W Other Storage Media These devices handle both input and output functions. Menu

Support Hardware Power Supply UPS Surge Arrestor Switch Box
And finally, devices whos job is to support the system. These are neither Input, output, or processing devices.

CPU Support Components

Transistors The transistor is one of the most widely used components. The example shown is a “discrete” transistor, meaning that it is an independent device. Transistors have a special property allowing them to conduct electricity under certain controlled conditions. The trick is controlling the conditions, which then allows us to control other devices and circuits. We can connect many transistors together to form larger circuits that can perform some sort of logic operation. All transistors have three leads, usually called the emitter, the collector, and the base. Transistors have many special characteristics that make each type suitable for different tasks.

Resistors Resistors are the simplest electrical components. They are used to limit current, or the flow of electricity. As their name implies, they “resist” current flow. The amount of resistance they present is measured in “ohms”. For instance, you would say of a resistor: “It’s a 470-ohm resistor.” Having resistance means that they use power, which is turned into heat. Most small resistors, as shown, don’t get very warm; these are typically called ¼-watt resistors. Resistors come in all shapes and sizes, those shown here are typical of regular consumer electronic devices. Some are very large and have special devices attached to help dissipate heat. Notice the colored stripes on these resistors. The colors are used as a code to determine the value of the resistor.

Color Codes Here is a chart depicting the resistor color codes.

Potentiometers A special type of resistor is the potentiometer, or variable resistor. The resistance value of this device is determined by where the control is turned. You use these all the time, in the form of volume controls, and other adjustment controls on devices such as monitors. Whenever you use a potentiometer, you are working with an analog circuit. Oftentimes, however, the potentiometer is the only analog component in a digital device…. Technicians call these “pots.”

Capacitors Capacitors are used to store charges and filter signals. The devices shown are typical small “caps.” You will see plenty of these in radios. Notice the small yellow capacitor is located next to an integrated circuit. These capacitors are used to filter noise out of the power applied to the IC. Capacitor values are measured in “Farads.” The farad is a very large unit, so nearly all capacitors have a value much less than one farad. For instance, the green capacitor labeled 104J has a value of .1 microfarads, or farads.

More Capacitors Another type of capacitor merits special attention. All capacitors can store a charge, but “electrolytic” capacitors, as shown, can store very large charges. In fact, they can store a charge large enough to hurt you. You must be careful if you are working on any device that contains electrolytic capacitors, especially big ones. Consider any capacitor larger than the last part of your little finger as large.

IC’s - DIP style Integrated Circuits are commonly called “ICs”, or just “chips.” They were revolutionary when introduced because they allowed many, many transistors to be built into one small device. The ICs shown are built into a package called a “dual-inline package,” or DIP for short. DIPs come in many sizes, from a total of four pins all the way up to and over 68 pins. DIPs are either soldered directly to a circuit board, or they are placed into sockets. Soldering them is more reliable in the long run, but makes them much harder to replace. Many BIOS chips are socketed DIPs on the motherboard.

The Clock Clock Chip 14.318 MHz Crystal BIOS System Clock
No digital circuits will run without a clock, or some other similar signal. CPUs are no different, and a clock is an essential component of every motherboard ever built. The Clock circuit consists of two parts: a crystal that generates a signal at some known and fixed frequency, and a clock controller that can generate many different frequencies, once the crystal is running. Here’s how it works: Once power is applied to the motherboard, the crystal begins to oscillate at its specified frequency. All the crystal needs is power, and it will run all by itself. However, most motherboards need a clock signal much faster than MHz, and that’s where the clock chip comes into play. The clock chip takes the incoming crystal signal and can process that signal into many different frequencies. The BIOS tells the clock chip exactly what bus clock speed is required, and the clock chip dutifully generates the proper signal. For example, the CPU tells the BIOS “I’m a 400 MHz CPU, and I need a bus speed of 100MHz.” The BIOS accepts that information, then tells the clock chip to generate a 100 MHz bus signal. The clock chip responds by converting the MHz crystal signal into a 100 MHz signal, and then puts that signal out on the bus. At this point, the rest of the motherboard comes to life, and the computer starts to boot. BIOS

The History of Processors
In this next section we will discuss a brief history of the microprocessor, with special emphasis on the microprocessors found in personal computers.

The First Microprocessor
4004 by Intel in 1971 Designed as the core logic of a calculator Handled data 4 bits at a time Ran at 108 KHz 2300 transistors Memory: 640 bytes The first microprocessor dates back to 1971 when a small company named Intel designed a device called the It was originally designed to be the core logic for the small electronic calculators, which were just becoming affordable at that time. Unlike prior control logic devices, which were designed for a particular purpose, the 4004 was a general purpose device whose characteristics could be controlled by a small program in ROM. By today’s standards it was extremely primitive, handling only four bits of data at a time and operating at speeds of about 100 kilohertz. It contained about transistors on a single chip of silicon and could handle only 640 bytes of memory. Just to emphasize that last item, that was 640 bytes.

8008 Date Introduced April 1972 Number of Transistors 3,500
Internal Register Size 8-bits Data I/O Bus Width 8-bits Maximum Memory 16 KB Typical Speed MHz A few months later, Intel introduced the first 8-bit microprocessor, the It was an expanded version of the 4004, which handled 8 bits at a time over an 8- bit bus. It contained nearly twice as many transistors and operated at almost twice the speed of the But perhaps its greatest advance was its ability to address up to 16K bytes of memory. This allowed much more complex control programs.

8080 Date Introduced April 1974 Number of Transistors 6000
Int Register Size 8-bits Data I/O Bus Width 8-bits Maximum Memory 64 KB Typical Speed 2 MHz In 1974, Intel introduced a microprocessor with enough instructions, enough speed at 2 MHz, and enough memory at 64Kbytes to form the core of a primitive microcomputer. A small calculator company called MITS designed what is normally regarded as the first personal computer, the Altair, using the as its core. It was introduced to the world in Over the next few years, dozens of personal computer designs from other companies followed, most based on the Intel 8080 microprocessor.

8088 Date Introduced June 1979 Number of Transistors 29,000
Int Register Size 16 bits Data I/O Bus Width 8 bits Maximum Memory 1 MB Typical Speed 8 MHz Between 1974 and 1979, many additional microprocessors were introduced by Intel and other companies. But none was more important to the personal computer than the Intel 8088, which was introduced in Its internal 16-bit registers made it fast and powerful, while its external 8-bit bus made it and its supporting circuitry affordable enough for personal computer use. The 8088 is a 40-pin DIP package.

The 8088 was used in the first IBM Personal Computer
This unique combination of power and affordability prompted IBM to use the in its first Personal Computer. Introduced in August 1981, the IBM PC brought respectability and standardization to the fledgling personal computer market. Fortunately, IBM used off-the-shelf components in its design, which were available to everyone. Within months IBM-compatible “clones” began to appear. The evolution of the IBM-compatible computer has followed the evolution of the Intel family of microprocessors to this very day. So let’s continue the story of the microprocessor.

80286 Date Introduced May 1982 Number of Transistors 134,000
Int Register Size 16 bits Data I/O Bus Width 16 bits Maximum Memory 16 MB Typical Speed MHz The next important step in Intel’s microprocessor history was the introduced in It processed data internally 16-bits at a time and operated over a 16-bit external bus. It could address 16 Megabytes of memory and ran at about 12 MHz. It is notable because the second generation of IBM PC, the IBM AT, used this chip as its processor. The 286 is considered to be the second generation of microprocessor. An was developed, but it was not used in any significant computers.

80386 Date Introduced Oct. 1985 Number of Transistors 275,000
Internal Register Size 32 bits Data I/O Bus Width 32 bits Maximum Memory 4 GB Typical Speed 16/20/25/33 MHz The third generation began with the 386 family whose first members were introduced in This was another quantum leap in capability. Its internal registers were 32-bits wide as was its I/O bus. This allowed it to operate on four bytes at a time. Also, its upper memory limit of 6 Gigabytes seemed unlimited at the time. The 386 was the first processor to be packaged in a PGA package.

80386sx Int Register Size 32-bits Data I/O Bus Width 16-bits
Typical Speed 16/20/25/33 MHz The 386sx was a 386 on the inside, but a 286 on the outside. This device allowed Intel to build the latest 32-bit processor into computers that were capable of utilizing 16-bit motherboards. This allowed for major cost reductions, making the -sx an inexpensive alternative.

Math Coprocessors Fast circuits to perform floating point math
For 8088 through 80386, a separate device As complicated as the CPU itself To understand the fourth generation microprocessors, we must first talk about Math Coprocessors. The math coprocessor is a special circuit designed to perform floating point arithmetic. Floating point refers to fractional numbers and exponents as opposed to only integer or whole numbers. Initially, the math coprocessor was a separate integrated circuit because its complexity approached that of the microprocessor itself.

CPU and Coprocessor For example, the 8088 had a separate coprocessor called the The had a sister chip called the Finally, the had a separate math coprocessor called the

80486 Date Introduced April 1989 Transistors 1,200,000
Int Register Size 32-bits Bus Width bits Max Memory 4 GB Typical Speed 66 MHz L1 Internal Cache 8 KB Math Coprocessor Internal However, starting with the 80486, the math coprocessor became a part of the microprocessor itself. Not every model of the 486 had the coprocessor, but many did. In most other respects, the 486 was just a faster version of the 386, as you can see here. Oh, there was one other important difference. The 486 also had an on-board cache memory.

Internal Cache A small memory inside the CPU that runs at the same speed as the CPU Also called an L1 cache The internal cache memory is a high-speed memory that is built right inside the microprocessor itself. Because this small memory is able to keep up with the processor, it can significantly increase the overall speed of the system. All processors since the 486 have included an internal or L1 cache.

Today’s CPU Standard

Pentium® Date Introduced March 1993 Transistors 3,100,000
Int Register Size 32-bits Data I/O Bus Width 64-bits Maximum Memory 4 GB Typical Speed MHz L1 Internal Cache 2×8 KB Internal Coprocessor Yes In 1993, the fifth generation was ushered in by Intel’s Pentium microprocessor. Its I/O bus was twice the width of the 486. The 64-bit system bus allowed 8 bytes to be transferred at a time. It also contained two 8 KB internal caches, one for instructions and one for data. Introduced with a clock rate of 60 MHz, its speed was increased over the years to 200 MHz. The Pentium was also notable because it was the first in the Intel family to execute more than one instruction at a time.

Number of clock cycles needed to execute a typical instruction
Another way to increase processor speed is to reduce the number of clock cycles required to execute an instruction. This slide compares the number of clock cycles required to execute an average instruction in various versions of Intel processors. Notice that the 8088 required 12 clock cycles, whereas, the 286 and 386 required only about four and a half. The 486 cut the number of clock cycles to about two, while the Pentium reduced it to about one. The average can be reduced to one because more than one instruction is processed at any given time.

This is a photo of a Pentium I in its socket
This is a photo of a Pentium I in its socket. The Pentium I is always covered by a heatsink and a fan.

Pentium MMX Date Introduced January 1997 Transistors 4,100,000
Internal Register Size 32 bits Data I/O Bus Width 64 bits Maximum Memory 4 GB Typical Speed MHz L1 Internal Cache 2×16 KB Math Coprocessor Yes MMX Instructions Yes In January of 1997, the MMX version of the Pentium was introduced. It was basically a very fast Pentium with 57 new instructions for handling Multi- Media operations. Also, the data and instruction cache sizes were increased to 16 kilobytes each.

Pentium Pro® Date Introduced November 1995 Transistors 5,500,000
Internal Register Size 32 bits Data I/O Bus Width 64 bits Maximum Memory 64 GB Typical Speed MHz L1 Internal Cache 2×8 KB Math Coprocessor Yes L2 Cache KB The sixth generation of microprocessor started with the Pentium Pro in November of Its greatest claim to fame is that it was the first of the Intel family to include the L2 cache in the same package, although not on the same chip, as the microprocessor. The L2 cache is normally an external cache memory that is much larger than the internal or L1 cache. It is much faster than DRAM, although not generally as fast as the internal or L1 cache. Another first for the Pentium Pro: It can handle up to 64 Gigabytes of memory.

Pentium Pro® Micro- 256 KB processor Cache
The packaging is unique among the Intel family. The microprocessor and L2 cache sit side-by-side in a single package. By embedding the cache in the same package with the processor, the cache can run at a higher speed. Also, the cache operates on a different bus from the normal system bus. This is often referred to as dual independent bus architecture.

Pentium II® Date Introduced May 1997 Number of Transistors 7,500,000
Int Register Size 32 bits Data I/O Bus Width 64 bits Maximum Memory 64 GB Typical Speed MHz L1 Internal Cache 2×16 KB Math Coprocessor Yes L2 Cache KB The Pentium II, first introduced in May of 1997, is a variation on the Pentium Pro theme. It used a new processor code named “Klamath” by Intel. It was much like the Pentium Pro but with the MMX instructions added and the larger L1 cache of the Pentium MMX.

Pentium II Single Edge Contact (SEC) Cartridge
The Pentium II comes in a new package that looks more like a game cartridge than a microprocessor. This new package is called a single edge contact or SEC cartridge. The CPU on the left is the original Pentium II. Later, Intel changed the Pentium II package to the style shown on the right. The Pentium III also uses this new package.

Internal View (Front) Cache Memory Pentium II Processor Cache Memory
Inside the plastic and metal housing, the Pentium II looks like this. The Klamath microprocessor is mounted on a small printed circuit board between two large memory chips, which serve as half of the cache memory. Two additional cache memory chips are soldered to the other side of the board. This approach is much more cost effective than the Pentium Pro Packaging and it allows Intel to use off-the-shelf memory chips for the cache. The cache runs at one-half the processor speed, over an independent bus called the “backside” bus.

Fan Heat Sink Pentium II SEC Cartridge
This unique package plugs into a special socket called Slot 1. Normally a fan and heat sink are added to aid in cooling. Pentium II SEC Cartridge

Pentium III ® 0.25 Micron Technology 450 MHz to 1.4 GHz
1.8V core voltage Dissipates less heat Supports multi-processing Pentium III is a faster version of the Pentium II. By using a smaller geometry, a faster, lower-voltage, and cooler-operating processor is possible. Speeds of 1,000 MHz or higher are currently available. Caches of 2 Mbytes are also now available.

Pentium 4 ® 0.18, 0.13, 0.09 Micron Technology
1.3 GHz to 4 GHz and higher 1 V to 1.8 V core voltage Dissipates lots of heat (up to 100 W) Supports multi-processing Pentium 4 is a completely upgraded version of the Pentium III. By using yet a smaller geometry, a faster clock, and lower-voltage, amazing speeds can be accomplished. However, the Pentium 4 uses a lot more power than most of its predecessors, requiring large heatsinks with fans.

Fan Heat Sink The Pentium 4 takes a lot more motherboard space than previous processors, largely because it requires a very large heatsink.

Celeron Intel has introduced a low-end processor called the Celeron. It is offered with no cover, and no heat sink. The original model had no L2 cache at all, although models with small L2 caches are available. Celeron is intended to compete with AMD and Cyrix for the low-end processor market, however the Celeron CPUs often perform nearly as well as a regular Pentium of the same speed. The original Celeron processors were terrible, but the second generation is a great buy! The bare CPU is shown at the top. In this brief review we have left out dozens of interesting microprocessors that have played significant roles in the evolution of the personal computer. However, we have covered the more important members of the Intel Family. Menu

AMD’s K6-2 One of the most popular non-Intel CPUs used in consumer PCs is the AMD. It is an less expensive CPU than Intel’s equivalent, and AMD claims that it is just as fast as any Pentium. The model shown here is a 500 MHz processor, which was part of a name-brand PC that cost just over $500.

Power and Connectors

This is your standard computer power supply
This is your standard computer power supply. One end plugs into the wall outlet, where 120 volt alternating current (VAC) is provided, and the other end provides low-voltage direct current. The connector on the bottom is used for a standard three-wire line cord. The top connector uses a special line cord that is designed for your monitor…this allows you to power your system with only one line outlet. Unless you have an electronics degree, a technician never opens the power supply. Consider it a replaceable, unrepairable module. The fans in common power supplies can fail, and when they do you replace the entire supply. Power supplies are cheap, and the circuits inside are dangerous. Standard Power Supply

Power Selection Switch
Most power supplies have a switch on the rear panel. This switch allows the system to be used with the two different AC line voltages. In North America, the switch should always be in the 115 position. Some supplies call it 110, some 120. They all mean the same thing. The 230 position is used in other parts of the world. This setting normally requires a different type of line cord.

WARNING! Hazardous voltages contained within this power supply, not user serviceable. Return to service center for repair. Pay attention to this warning, which is on nearly every power supply ever built. There are hazardous voltages present, even when the supply is not attached to the wall outlet. The circuits inside a power supply can store dangerous charges, which are hazardous if not handled properly. Don’t open the power supply case.

Power Supply Connectors
There are many colored cables coming out of the power supply. They connect to the motherboard and the drives. Sometimes the CPU fan is connected to one of these cables, and other internal peripherals may be attached as well. Power Supply Connectors

Power Supply Output Voltages AT-Type
+5 Volts +12 Volts -12 Volts -5 Volts The AT-type motherboard required these four voltages from the power supply. This is a throw back to earlier times when these voltages were actually used on the motherboard. With today’s lower voltage integrated circuits, these voltages are maintained for compatibility purposes. They are still part of the ISA and other interface standards, even though some of these voltages are no longer used on the motherboard itself.

On the AT-type motherboard and many other types as well, power is supplied to a single connector like that shown here. From this connector power is distributed throughout the board by way of circuit board traces. AT power connector

Edge View of Motherboard
Most circuit boards have multiple layers with one or more layers set aside for power distribution.

Voltage Regulator Frequently you will find voltage regulators on these types of motherboards. This is necessary because the many modern integrated circuits require lower voltages than the +5 volts from the power supply. These regulators convert the DC voltages from the power supply into the even lower values of DC voltage required by the motherboard circuits.

Motherboard Power Connectors
Black Wires The connectors from the AT-type power supply to the motherboard most often take this form. There are two connectors, usually labeled P8 and P9. They plug into a single jack on the motherboard. Unfortunately, they can be connected incorrectly. The correct connection is with the black leads side by side in the middle as shown here. Another way to remember the correct connection is that P9 should always be closest to the edge of the board. P8 P9

P9 -5V +5V +5V +5V Ground Ground
The motherboard power connectors often have a latch that holds them securely in place. Look for these latches and release them before you attempt to disconnect power from the motherboard. P9 connects the +5 volts and the –5 volts to the motherboard. P9

P8 +12V -12V +5V Power Good Ground
P8 connects the +5 volts and the plus and minus 12 volts as shown here. Multiple connections are used for the +5 volts because of the heavy current required from this supply. Another important signal carried by P8 is the Power Good signal.

The Power Good Signal +5 Volt signal generated by the power supply
Indicates that the power supply passed its self test and its output has stabilized Occurs within first 0.5 seconds Prevents system from running under bad or unstable power conditions The Power Good signal is generated during the Power On Self Test. When this signal reaches +5 volts, it indicates that the required voltages are present and that they have stabilized to the point of being usable. This normally occurs within the first half-second or so after the computer is turned on. The purpose of the Power Good signal is to prevent the system from running with bad or unstable supply voltages. The CPU won’t start until the power good signal occurs.

Large Molex Connector Power is distributed to other parts of the computer via two types of connectors. The most common is the Molex connector. The Molex connector is used to supply power to the hard drive, the CD-ROM drive, and sometimes the cooling fans. Often you will find extra Molex connectors that are not connected to anything. These are supplied for future expansion such as adding an additional hard drive. Every Molex connector has the same voltages; these connectors are always interchangeable.

4-Pin Molex Connector +12V Ground +5V
The voltages supplied by the Molex connectors are +5 volts and +12 volts. The +5 volts are required by the electronic circuits in the hard drives. The +12 volt lines are required by the drive motors in the hard drives and in the fans. Ground +5V

Berg Connector Another common connector is the smaller Berg connector. Its primary purpose is to supply power to the floppy drive. Both the Molex connectors and the Berg connectors are keyed so that they cannot be easily connected backwards.

4-Pin Berg Connector +5V Ground +12V
Like the Molex connector the Berg connector also carries +5 volts and +12 volts. The +5 volt line supplies the electronics in the floppy drive while the +12 volt line supplies the drive motor. Ground +12V

Grasp the connector by the shell…
never by the leads To prevent damage to the delicate leads, it is important that you grasp the connectors by their shells rather than by their leads.

Power Supply Output Voltages ATX-Type
+5 Volts +12 Volts -12 Volts -5 Volts +3.3 Volts The ATX Power Supply is a little different in that it supplies a lower voltage (+3.3volts) that is more in keeping with the lower requirements of modern motherboards. All PC systems based on the Pentium II CPU should have an ATX power supply.

ATX Power Connector The power connection to the motherboard is also simplified by using a single 20-pin connector rather than the two 6-pin connectors required by the AT-type board. Because the supplied voltages and connectors are different, the AT and ATX power supplies are not interchangeable.

ATX Power Connector Menu
The ATX motherboard has a single 20-pin power connector. If you look closely, you will notice that this connector will not allow the cable to be attached incorrectly. Menu

When Things go Wrong!

The Power Supply Don’t fix it Don’t open it It isn’t worth it!
Only use UL or CSA approved supplies Unless you have an electronics degree you should stay out of power supplies. They are too cheap to be worth repairing, even for those who have the requisite knowledge to properly repair them. The time it takes to troubleshoot a power supply is completely offset by the cost of a new supply. The problem is that a PC power supply can store a charge sufficient to cause you great bodily harm, well after it is unplugged. The large capacitors can hold a charge for many days. Some designs are safer than others, but unless you are experienced in discharging capacitors, and understand their time constants, you should not mess with them. The UL and CSA approvals, in their basic sense, provide that the device will not catch on fire and that if it fails it will do so safely. The approvals do not mean that the device is foolproof, only that it will die quietly and that it does not present any inherent danger during proper usage. Proper is the key word.

Check Fan Operation The heat generated inside the PC is regulated for the most part by fans. Cooler outside air is moved through the computer in exchange for the hotter internal air. Whenever you have the computer open (for whatever reason), it’s a good idea to check the fans. Check the CPU fan (if there is one) and other fans in the system. Make sure they are running. If they are not running, they may have to be replaced or possibly they are unplugged from their power source. You should also check that the fans are not clogged with dust. If they are, then you probably need to blow out the dust from inside the PC, too.

Power Surges and Sags are both serious problems...
Bad News... 120VAC You can’t control the quality of the power your power company delivers to your facility or that mother nature affects. But there are steps you can take to prevent power surges and sags... Your computing equipment generally likes AC power around 120 volts or so. It will tolerate some variation but wide variances are common and can do considerable damage. A surge occurs when the AC power is much higher than 120VAC. It may be just for a fraction of a second but that is long enough to harm computer equipment. A sag occurs when the AC power drops below 120VAC. This happens when a heavy load comes on line (like during hot weather when air conditioners near your facility are turning on and off). Power conditioning equipment can prevent these problems and is a good investment. Bad News...

Static Electricity and the Computer

Your greatest enemy when working in the computer is Electrostatic Discharge or ESD.
Let’s spend a moment talking about electrostatic discharge or ESD. When working inside the computer, more damage is done by electrostatic discharge than by any other single factor. In fact, any time the computer is open, you risk damaging the circuits inside by electrostatic discharge. That’s the bad news. The good news is this risk can be almost totally eliminated by a few common sense precautions.

Your best defense against ESD is the anti-static wrist strap.
Your first line of defense is the anti-static wrist strap. It is a simple conductive strap. One end fits around your wrist; the other is clipped to ground on the computer. It will drain off any electrical charge that attempts to accumulate. It keeps your body and the computer chassis at the same potential, virtually eliminating the risk of ESD.

An internal resistor provides shock protection.
If you are concerned about deliberately grounding your body when working around electronics, set your mind at ease. A resistor built into the wrist strap limits the current to a safe level should you inadvertently brush against a live terminal. With this resistor you are not connected directly to ground, there is a resistor in-between which will limit the current to a safe level.

Switch off power at the computer and at the workbench...
While the anti-static wrist strap greatly reduces the risk of ESD damage, there are some other precautions that should also be taken. Obviously, you should turn off power to the computer and those devices connected to it before you disconnect anything from the computer.

...but leave the computer plugged in.
However, it is a good idea to leave the computer plugged in. The reason for this is that the ground-wire on the line cord will keep the chassis at ground potential. Any static charge you have accumulated while walking around the room will be safely dissipated when you touch a grounded chassis. But if the computer is unplugged and you touch the chassis after your body has accumulated a charge, the chassis will become charged as well. You can only unplug the computer if you use an anti-static mat…

Use anti-static mats on the workbench and floor.
If you have them, it is good practice to use anti-static mats on your workbench and on the floor where you will be standing. These are conductive mats, that when properly installed, will prevent the build-up of static electricity. When you use a properly installed mat you may safely work in the computer with the power cord removed.

Hold Circuit Boards by their edges
Circuit boards are especially vulnerable when they are unplugged from the computer. You should be very careful to handle the boards only by their edges. Avoid touching the components, the foil patterns, and the connectors on the board.

Store Circuit Boards in Anti-static Bags.
When not in use, boards should be kept in conductive anti-static bags. These simple precautions will go a long way toward eliminating the danger of ESD damage. 

General Safety Tips Look for UL or CSA labels Be careful around fans
Watch for sharp edges Double-check the power before removing or replacing anything This is all common sense, but it must be stated anyway. The UL/CSA labels indicate that the unit was designed in a safe manner. It does not mean that the unit is perfectly safe, because a previous technician or user could have inadvertently created an electrical hazard. The UL and CSA designations are expensive to obtain, so you may not see them on low-end equipment. The hazard with fans is obvious, but the danger is not. You are unlikely to hurt yourself on a fan, but your reaction to a brush against the fan might cause you to hurt yourself. It’s the secondary damage that can hurt you, as you involuntarily jerk your hand away from the fan and scrape it against a sharp edge on the way out. Speaking of sharp edges, there are plenty of them in a PC. Watch for them and avoid them. Installing or removing a component with the power on is likely to destroy two components. Never do it; always double-check. Do not become complacent as you gain experience.

The Power Supply Don’t fix it Don’t open it It isn’t worth it!
Only use UL or CSA approved supplies Unless you have an electronics degree you should stay out of power supplies. They are too cheap to be worth repairing, even for those who have the requisite knowledge to properly repair them. The time it takes to troubleshoot a power supply is completely offset by the cost of a new supply. The problem is that a PC power supply can store a charge sufficient to cause you great bodily harm, well after it is unplugged. The large capacitors can hold a charge for many days. Some designs are safer than others, but unless you are experienced in discharging capacitors, and understand their time constants, you should not mess with them. The UL and CSA approvals, in their basic sense, provide that the device will not catch on fire and that if it fails it will do so safely. The approvals do not mean that the device is foolproof, only that it will die quietly and that it does not present any inherent danger during proper usage. Proper is the key word.

Respect... not fear. The purpose of all this is not to cause you to fear a computer or monitor. While you need not fear such equipment, you should learn to respect it. By observing a few basic common sense safety rules, you can service this equipment in complete safety.

Disassembling and Reassembling a Computer

Why Disassemble the Computer?
To upgrade. To repair. To add to it. You may be wondering: “Why would I want to disassemble a computer in the first place?” There are several reasons why you will have to do some level of disassembly. Perhaps the most frequent reason is to upgrade. Computer technology changes very quickly. That state of the art computer you buy today may be out of date in a year and obsolete in two, unless it is upgraded. The best way to extend its useful life is to upgrade it frequently. This may include adding more memory, changing to a larger hard drive, or going to a faster modem. Another reason for disassembly is repair. Computers break. A hardware malfunction inside the computer requires some level of disassembly. Finally, you will have to do some disassembly to add a new capability such as a sound card, a CD-ROM drive, a modem, or a network card. In this exercise you will completely “field strip” the computer so that you can become familiar and comfortable with the procedures involved.

The three most important things to remember when disassembling a computer are:
Document Document! The most important thing to remember when disassembling a computer is to document everything. It is embarrassing and sometimes costly to forget how everything goes back together. Your chances of getting everything back together properly increases dramatically when you have clear, detailed documentation of what goes where.

Document Where cards are located. How cables are routed.
Orientation of cables and connectors. Hardware used to secure each component. Anything else that might cause confusion when reassembling. In particular, you should document where the various cards inside the computer are located; how the cables are routed and oriented; the hardware used; and anything else that might cause confusion when you start putting things back together.

Turn off power to the computer and everything connected to it.
The first step is to turn off power to the computer and to anything else that is connected to it such as the monitor and printer. Never connect or disconnect cables from “live” equipment.

Disconnect the monitor and set it aside.
Once power is removed, disconnect the external cables. Disconnect the monitor and set it aside. The monitor is connected to the so-called VGA connector on the computer. Once disconnected you can recognize the VGA connector by its fifteen pins, arranged in three rows of five pins each.

Disconnect the keyboard and set it aside.

Disconnect the mouse and set it aside.
Disconnect the mouse and set it aside. This computer uses a serial mouse that connects to the COM1 serial port. The connector is a 9-pin D-shaped affair with the male end connected to the mouse.

Remove these screws... Once everything is disconnected, you are ready to remove the cover. On this computer, the cover is held in place by four screws that are accessible from the back of the unit. Look for the four screws along the narrow lip of the cover where it overlaps the back of the computer indicated here by the arrows.

... not these. Be very careful that you do not take these screws loose by mistake. These hold the heavy power supply in place as you will see later from inside the computer.

With the cover off, the inside of the computer looks something like this. There are five main items that are of immediate concern.

The Motherboard The large board that occupies the lower left quarter of the chassis is the motherboard. This single board contains the microprocessor, the various buses, and the interface circuitry. It also provides bus slots and sockets for a wide range of expansion boards.

Power Supply Input Voltage
100 to Hz 200 to 50 Hz Another very prominent item that is easy to find in any computer is the Power Supply. It is usually a metal cage with AC outlets accessible through the chassis on one side and a bundle of colorful cables on the other. The Power Supply converts the AC line voltage into low level DC voltages used by the various components in the computer. In today’s global economy, the manufacturer of the computer is never quite sure where the computer will end up. Most computers use a power supply that will accept either 115 Volts AC or 220 Volts AC so that it will work in a variety of countries. On this computer, a switch on the back of the power supply just above the power cord selects the proper AC input voltage. Switch Selectable

Some connectors are held in place by a latch.
A necessary step in disassembling the computer is to unplug these various power connectors. Care should be taken when doing this. First determine whether or not there is a latch holding the connector in place. If so, you must lift the latch with a small screwdriver before attempting to wiggle the connector loose. Latch

Grasp the connector by the shell…
…never by the leads. Second, grasp the connector by the plastic shell. Wiggle it up and down and end to end while pulling slightly on the shell. Never pull the wire leads.

The Power Supply is held in place by four screws.
The power supply is connected to the chassis by four screws. Once these four screws are removed, the power supply can be lifted out of the computer.

The Hard Drive may be located here ...
Next you will remove the hard drive. Depending on your computer, the hard drive may be located here…

… Or here. Or here.

Where ever it is located it will have two cables attached; the power cable and a 40-pin, flat-ribbon cable. Notice that the flat cable has a stripe on one side. This identifies the edge of the cable that contains pin 1. Be sure to document the orientation of this cable before disconnecting it from the hard drive. Once the cables are disconnected, the four screws that hold the drive to the chassis can be removed and the drive can be lifted out of the computer.

The Floppy Drive Next you will remove the floppy drive. Like the hard drive, it has a power cable and a flat ribbon cable and it is held in place with four screws. Once everything is disconnected, slide the floppy drive out the front of the computer.

Some additional cables connect to various other points on the motherboard. These are described in the step-by-step procedure in your Workbook.

Screw Standoff Once all cables and boards are disconnected, the motherboard itself can be removed. It is held in place by three screws and two standoffs. As soon as it is removed, it should be placed in an anti-static bag.

Keep these tips in mind Document everything. Shut off power.
Protect against ESD. Grasp connectors by shells-not leads. Never use force. Release latches on connectors. Rock boards end to end. Well, there you have it. You are now ready to try your luck at disassembling the computer. Keep these tips in mind as you do it. Document everything in enough detail so that you can put the computer back together again. Shut off the power before disconnecting anything. Protect against electrostatic discharge. The best way to do this is to wear an anti-static wrist strap. When removing connectors, grasp them by their shells; never pull on the leads. Never use excess force. If something doesn’t come loose using reasonable force, look for latches, tabs, or screws holding it in place. Remove daughter- boards from the motherboard by rocking them end-to-end. With a few reasonable precautions, you can take the computer apart and then put it back together again so that it works the first time you turn it on.

General Knowledge, CPUs, and Safety

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General Knowledge, CPUs, and Safety

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