1. Exercise 2 The Motherboard
Welcome to Exercise 2. In this exercise you will learn to identify the most important components on the motherboard.

2. Motherboard Form Factors
AT-Type
Baby or Mini AT
ATX-Type
Proprietary Designs
PC motherboards come in various sizes and shapes. This is often referred to as their form factor. Here is a partial list of some of the form factors that have evolved over the years. For now, we will not be concerned with their specific shapes and sizes. Instead, we will concentrate on what they have in common. We will discuss two types of motherboards in this presentation. As you will see, they differ in size and shape, although they perform the same basic functions.

3. Proprietary Motherboard
The first is one of the proprietary designs.

4. ATX Motherboard
The other we will discuss is the ATX-type shown here. It is similar to the board in your computer trainer. These two types were chosen because they contrast well and they are very representative of many PCs found in the field today.

5. Some motherboards are designed for the original Pentium Processor
The layout of the motherboard is determined in part by the type of processor used. Some are designed for the original Pentium processor.

6. Others are designed for the Pentium II Processor
Others are designed for the newer Pentium II processor.

7. AT Motherboard with Pentium CPU
Let’s begin by looking at an AT motherboard that uses a Pentium processor. A typical example is shown here.

8. Power Distribution
Let’s begin by talking about power distribution.

9. AT-Motherboard Power Connectors
Black
Wires
There are two types of power connectors. With older AT-style motherboards, power is supplied to the motherboard by two connectors called P8 and P9. It is important to note the arrangement of these two connectors. Notice that they are connected so that the black wires in P8 are adjacent to the black wires in P9. Connecting them in the opposite direction is a recipe for disaster.
AT-Motherboard Power Connectors

10. Power Connector
The motherboard has pair of connectors that accept P8 and P9. Different brands on motherboard have this connector in different locations, and even different versions of the same type may have the connector in a different place. From these connectors, power is distributed by the printed traces on the motherboard.

11. Edge View of Motherboard
If you could see a magnified edge-view of the motherboard, it would look something like this. As expected, there are metal foil layers on the top and bottom of the board. However, there are additional metal layers inside the board. Voltages are distributed to where they are needed by these internal foil patterns.

12. Voltages supplied to the motherboard
+ 5 Volts
- 5 Volts
+ 12 Volts
- 12 Volts
The voltages supplied to this motherboard are +5 and –5 Volts and +12 and – 12 Volts. While this is in keeping with the original “PC Standard,” these are no longer the ideal values for modern computers. For example, Pentium and Pentium II CPUs now require 3.3 Volts or less. So do many of their support chips. This is necessary to limit the amount of heat produced by the MPU and its associated circuitry.

13. On many motherboards, an onboard voltage regulator reduces the +5 Volts to this lower value. In this example, you will find this regulator in the lower right corner of the motherboard. It is easy to spot because of the large heat sink.
Voltage Regulator

14. CPU Socket
You can’t miss the CPU socket, it’s the single largest part on the motherboard.

15. The MPU
Even without the fan attached, the Pentium MPU would be one of the most prominent features on the board. Roughly 2 inches on a side, it has well over 300 pins. This type of package is called a pin grid array, or PGA.

16. The Pin Grid Array (PGA) Socket.
You can see why it is called this from the top view of the PGA socket. Multiple rows of pinholes are arranged in an array, like a grid on graph paper. Often the pins on the MPU and the holes on the socket are staggered to allow even closer spacing. In that case, it is called a staggered pin gate array. The socket is usually keyed with missing holes as shown by the arrow so that the MPU cannot be inserted incorrectly.

17. MPU
int e l
Socket
Lever
Another term used to describe the MPU socket is Zero Insertion Force, or ZIF. This refers to a type of socket like the one shown here. It is specially designed to make replacement of the MPU as easy as possible. A lever on the side of the socket releases the pins of the MPU so that the chip can be lifted out. 17

18. 2. 1.
int e l
The replacement procedure goes like this. After taking ESD precautions, lift the lever and then gently lift the MPU out of its socket. 18

19. 3.
int e l
Gently insert the new MPU into the socket, being careful to align it properly. 19

20. 4.
int l e
Pull down the lever to lock the MPU in the socket. 20

21. Fan
Heat Sink
You will also have to be concerned with the heat sink and fan that attaches to the top of the MPU. But for now let’s turn our attention to some of the other features of the motherboard.
CPU 21

22. Industry Standard Architecture (ISA) Bus.
8-MHz Speed
Supports 8-bit and 16-bit data transfer
Used for slow speed operations such as modems and sound cards.
Let’s begin by looking at the ISA bus. ISA stands for Industry Standard Architecture. Dating back to the early 1980’s, it is old and slow technology. It survives today because so many ISA boards are in existence. It operates at 8- MHz and supports only 8-bit and 16-bit data transfer. Pretty poor by today’s standards, it is fast enough for slow tasks such as handling modems and sound cards.

23. This example shows three ISA slots.
ISA BUS

24. 16-bit Cards
8-bit Cards
If you look closely at the ISA bus slot you see that it is divided into two sockets in a single shell. It evolved this way so that it could handle even older 8-bit interface cards as well as newer 16-bit cards. The 8-bit cards plug into the front socket while 16-bit cards use both sockets. 24

25. ISA boards installed. 16-Bit 8-Bit Motherboard
Here you see how an ISA bus might look with an 8-bit card in the foreground and a 16-bit card in the background.
Motherboard

26. Peripheral Component Interconnect (PCI) Bus
33 MHz
Handles 32-bit and 64-bit data transfers
Processor independent
Supports Plug and Play
A more modern technology is the PCI bus. PCI stands for Peripheral Component Interconnect. It operates at 33 MHz and normally transfers data 32-bits at a time. A version that can handle data transfers up to 64-bits wide also exists, but is not in common use at the time of this writing. PCI uses a bridge circuit between the CPU and the PCI socket so that (in theory, at least) it is processor independent. Also, it supports Plug and Play. This is a feature that allows software to configure the computer and the PCI cards automatically.

27. PCI BUS
This example has 4 PCI slots. Although shorter than the ISA slots, they have more pins to accommodate the wider data and address buses.

28. SIMMs
Further up the motherboard are four more sockets that look like a bus of some kind. Actually these sockets are for memory modules called SIMMs. SIMM stands for Single In-line Memory Module.

29. Single In-line Memory Module (SIMM)
A typical SIMM consists of a small circuit board with up to about nine ICs on board. They plug into the motherboard via the 72-pin edge connector. These SIMMs are 32-bits wide. Because the Pentium data path is 64-bits wide, the SIMMs are installed in pairs. These SIMMs make up the system RAM.

30. Cache
Memory
But the SIMMs are not the only memory on the motherboard. The two ICs shown here make up the external or L2 cache memory. Unlike the SIMMs which use dynamic RAM or DRAM, the cache uses static RAM or SRAM. Static RAM is much faster than dynamic RAM. By keeping the program that is currently running in this high-speed cache memory, the speed of the overall system can be increased.

31. The Chip Set
The support chips that make the microprocessor a microcomputer.
Applications Specific Integrated Circuits (ASICs) that provide the signals, controllers, interfaces and buffers that the system needs to operate.
In spite of all the advances in microprocessors, they still need additional support circuits to form a complete computer. Collectively, these support circuits are called the chip set. More specifically, the term chip set refers to a special set of Application Specific Integrated Circuits or ASICs that add the functions needed to convert the microprocessor into a microcomputer.

32. Chipset
Here, the term chipset refers to these two ICs. Intel, the manufacturer of these ICs, calls them the PCI set. They are designed specifically to enhance the capabilities of Intel’s Pentium processor to a full-blown microcomputer.

33. Main functions of the Chipset
A System Controller handles timing, interrupt and DMA control, and power management.
A Memory Controller provides interconnection and control of memory systems.
A Peripheral Controller connects the MPU to internal and external devices such as disk drives, buses, and peripherals.
The three main functions performed by the PCI set are these. A System Controller handles the overall timing, control, and power management functions. A Memory Controller interconnects and controls the complex memory system. A Peripheral Controller connects the MPU to the various buses, disk drives, and external peripherals, often with the help of additional support circuitry.

34. Super I/O
Controller
One of these additional support chips is called the Super I\O Controller.

35. Super I\O Controller Interface to the floppy drive.
Interface to serial ports.
Interface to parallel ports.
It contains the interface circuits for the floppy disk drive, the serial I/O ports, and the parallel port.

36. Keyboard
Controller
A separate IC is also used to control the keyboard.

37. Keyboard Controller
Communicates with the microprocessor in the keyboard.
Performs a parity check.
Converts serial data from the keyboard into the parallel data needed by the computer.
Generates an interrupt to alert the system that a key has been depressed.
Some of the functions performed by the keyboard controller include these. It communicates with the tiny microprocessor inside the keyboard. It does a parity check on data received from the keyboard. It converts the serial data from the keyboard into the parallel data required by the computer. And it alerts the MPU that a key has been depressed by generating an interrupt request.

38. ROM
BIOS
Another particularly important IC on the motherboard is this one. It is called the ROM BIOS. Recall that ROM stands for Read Only Memory and BIOS stands for Basic Input Output System. The BIOS is really a small program held in this ROM that controls the most primitive level of communications between the processor and the I/O devices. When you boot the computer, the BIOS program runs the Power On Self Test, or POST. During this test, it checks out many functions of the overall system to ensure that everything is working properly.

39. Identifying the ROM BIOS.
Socket
Version #
R3.60
You can generally spot the ROM BIOS by one or both of the following signs. First, it is often in a socket so that it can be easily updated. Second, it will often have a version number on a stick-on label right on the ROM IC itself. For example, in your computer, the stick-on label might read R3.60, indicating the revision number.

40. Electrically-Erasable PROM… EEPROM
Here are two photos of what you might see on an AT motherboard. These two photos represent two different BIOS manufacturers, AMIBIOS and Award.

41. Real Time
Clock
One final component that deserves some mention is this one – the real time clock. When a new computer is taken out of its shipping carton and plugged in, it often displays the correct time and date. The reason for this is that it has a battery powered real time clock that was set by the manufacturer or the distributor of the computer. In some computers the battery is accessible, making it easy to change. In others, the battery is inside the real time clock package and the entire package must be replaced should the battery fully discharge. Fortunately the battery is said to last for about seven years, so the computer may be obsolete before the battery needs replacing.

42. The Real Time Clock (RTC) contains:
CMOS memory
And in some cases the battery.
In addition to the clock (and in some cases the battery), there is a tiny CMOS memory in the real time clock that is kept alive by the battery, even when power has been removed from the computer. However, the time and date information takes up only a few bytes of the CMOS memory.

43. CMOS is used to hold SETUP information.
The remaining CMOS memory is used to store data about the configuration of the computer called the Setup information. Today, this tiny memory that is kept fresh by the battery is called the CMOS and the information stored is called the SETUP. You will learn much more about this later.
Those are the major components on the motherboard. Obviously there are a few other odds and ends that form the glue that holds everything together.

44. The FRUs on the Motherboard include:
The MPU
Any board plugged into the PCI bus.
Any board plugged into the ISA bus.
The SIMMs
The ROM BIOS
Of the various components on the motherboard, several can be replaced so easily that they are called Field Replaceable Units, or FRUs. Basically, this is anything that is not soldered down. So, the FRUs include: the MPU and its fan, any board that is plugged into the PCI or ISA bus, the SIMMs, and the ROM BIOS.

45. 9.6 ”
pentium II
intel
ATX Motherboard
12 ”
Now let’s consider the ATX-type motherboard and see how it differs from the earlier design. A typical example is shown here. You may recognize this as the motherboard used in your computer trainer. It uses the newer Pentium II, III, or 4 processor although older Pentium versions also exist.

46. Power Distribution
Aside from its shape and size, another way to recognize the ATX design is by its power distribution.

47. ATX-Motherboard Power Connector
The ATX motherboard uses a single connector to replace the two connectors shown before. In many cases it is labeled P1, as shown here, but not always.
ATX-Motherboard Power Connector

48. Motherboard Power Connector
Power is supplied to the motherboard via a single 20-pin connector rather than the two connectors used with the earlier design.

49. The power connector plugs in here on the motherboard
The power connector plugs in here on the motherboard. On your computer trainer, this socket is keyed so that the connector cannot easily be plugged in backwards.
Power
Connector

50. Power Supply Output Voltages ATX-Type
+5 Volts
+12 Volts
-12 Volts
-5 Volts
+3.3 Volts
The PS/2 type power supply used by the ATX boards produces an additional voltage, +3.3 Volts DC. Recall that the 3.3 Volts is not produced in the AT-type power supply.

51. Pentium 4,
Heat Sink & Fan
Of course the most prominent feature on this ATX motherboard is the Pentium 4 microprocessor. Its large heat sink and fan add to its commanding appearance.

52. ISA Bus?
Where is the ISA bus? This Pentium 4 motherboard has no ISA slots.

53. PCI Bus
By contrast, 5 of the much faster PCI slots are provided.

54. AGP
The latest wrinkle in expansion slots is the Accelerated Graphics Port or AGP, so named because of its use with accelerated graphics cards.

55. Accelerated Graphics Port (AGP)
Operates at twice the speed of the PCI bus or at 66MHz.
Even higher speed versions are being developed.
Presently used only by Video Cards
In its most basic form, the accelerated graphics port operates at twice the speed of the PCI bus. Also, even faster versions are being developed. While AGP is used only as a graphics port at present, there is talk of it eventually replacing PCI.

56. Another step up from the motherboard shown earlier is in the memory or RAM. As with most Pentium II, III, and 4 based machines, your computer trainer uses DIMMs rather than SIMMs. Whereas, the SIMM is a Single In- line Memory Module, the DIMM is a Dual In-line Memory Module.
DIMMs

57. Dual In-line Memory Modules (DIMMs) have components and pin
connections on both sides of board.
When viewed from this angle, the DIMM looks much like the SIMM shown earlier. However, the DIMM has components and pin connections on both sides of the small printed circuit board. It is a bit like two SIMMs glued back to back. The DIMM is keyed so that it will not fit into a SIMM socket.

58. Chipset
The Chipset has basically the same functions as the older Pentium design plus the added responsibility of handling the Accelerated Graphics Port.

59. Super I/O
Controller
The Super I/O Controller is located here…

60. ROM BIOS
Battery
And the ROM BIOS is located here. In your computer trainer, the backup battery for the CMOS and the real time clock is easily accessible.

61. I/O Ports
Another distinctive feature of the ATX motherboard is that all the I/O ports are located together.

62. I/O Ports
10101
So if you look at the back of the computer and you see an arrangement like this, chances are good that there is an ATX-type motherboard inside.

63. The motherboard is the heart and soul of the computer.
But regardless of the type used, the motherboard is the heart and soul of the personal computer.