Chapter 6 The System Unit

Competencies (1 of 2) Describe the four basic types of system units Discuss how a computer uses binary codes to represent data in electronic form Describe each of the major system unit components Discuss microprocessors, including specialty processors Describe the different types of memory Page 154

Competencies (2 of 2) Discuss expansion slots and boards Describe the five principal types of expansion buses Discuss the four standard ports Page 154

System Unit Also known as the system cabinet is a container that houses most of the electrical components that make up a computer system. Page 155

Electronic Data and Instructions Data and instructions are represented electronically Two-state system or Binary System Off/on electrical states Characters represented by 0s (off) and 1s (on) Bits Bytes Our voices recognize analog (Key Term) signals Continuous signals Computers only recognize digital (Key Term) signals Electrical On/off state The binary system consists of two digits – 0 and 1 Each 0 or 1 is called a bit – short for binary digit Bits are combined into groups of eight bits called bytes Smallest character = bit; eight bits = 1 byte or one character Page 157

Binary Coding Schemes Three types of binary coding schemes ASCII - American Standard Code for Information Exchange EBCDIC - Extended Binary Coded Decimal Interchange Code Unicode – handles languages with large numbers of characters Knowing this information helps understand what takes place when data entered into computer – why it takes “so long” for the data to get transformed Three basic schemes of coding ASCII – primarily desktop EBCDIC – primarily mainframe and super Unicode – to handle languages with large numbers of characters Page 158

System Board Connects all components Allows communication between devices Main board or motherboard Circuit board electronic components Sockets Slots Bus lines Connects all system components and allows input and output devices to communicate with system unit Other names: main board; motherboard Located in the system unit, consists of a large flat circuit board with sockets and chips (Key Term) Chips contain numerous circuits etched on a small wafer of layers of silicon and other materials Chips are mounted on carrier packages (Key Term) Chips are also referred to as a silicon chip (Key Term), semiconductor (Key Term), or integrated circuit (Key Term) Page 159

Microprocessor Central Processing Unit (CPU) Two Basic Components Control unit Arithmetic-logic unit (ALU) Located on the microprocessor chip and has two components - the control unit and the arithmetic-logic unit Control Unit Program instructions Directs flow between memory and Arithmetic-Logic Unit Directs flow between CPU and I/O devices Arithmetic-Logic Unit - ALU Two types of operations Arithmetic operation (Key Term) Logical operation (Key Term) Microprocessor Chips Word size CISC RISC Smart Card (Key Term) Page 161

Microprocessor Chips Chip capacities are expressed in word sizes Two Recent Significant Developments 64-bit processors Becoming more commonplace Windows XP Professional X64 Edition Dual-Core Chips Can provide two separate and independent CPUs Parallel processing A word (Key Term) is the number of bits that can be accessed at one time by the CPU Older computers process data and instructions in millionths of a second – microseconds Newer computers Nanoseconds– microcomputers Picoseconds– supercomputers Page 162

Memory Holding area for data, instructions, and information Memory is contained on chips connected to the system board Types of memory chips RAM ROM CMOS RAM (Random-access memory) (Key Term) Frequently accessed Acts as high-speed, temporary holding area Faster processing results Temporarily holds data and programs being processed by the CPU Volatile - when power shuts off, contents of RAM are emptied Exception - flash RAM can retain data when power disrupted, used in high end portable computers Cache (pronounced: “cash”) Area in RAM set aside to store information frequently accessed Acts as a high-speed, temporary holding area for parts of programs and data Results in faster processing results for the user ROM (Read-only memory) (Key Term) Nonvolatile; CPU retrieves programs written on the ROM chip Typical user does not go in and change information on ROM Also called firmware CMOS (complementary metal-oxide semiconductor) (Key Term) Provides flexibility and expandability for system Page 163

RAM Random Access Memory (RAM) chips hold the program and data Cache memory or RAM cache Flash RAM or flash memory Other types of RAM DRAM SDRAM DDR Direct RDRAM Cache memory – improves processing by acting as a temporary high-speed holding area between the memory and CPU Flash memory – can retain data even if the power is disrupted Most expensive type of RAM Used for digital telephones, digital video cameras, and portable computers Virtual Memory (Key Term) – large programs are divided into parts and the parts are stored on a secondary device, usually a hard disk. Each part is then read into RAM only when needed RAM is also referred to as temporary or volatile storage It is a good idea to save your work in progress to a second a secondary storage device. which is permanent or nonvolatile storage Return Page 163

ROM Read-only memory (ROM) chips are not volatile and cannot be changed by the user CPU can read, or retrieve data and programs but the computer cannot write Contain special instructions Needed to start a computer Give keyboard keys their special capabilities Put characters on screen ROMs are also called firmware Return Page 164

CMOS Complementary metal-oxides semiconductor (CMOS) chips provide flexibility for a computer system Contains essential information every time the computer is turned on Date and time Amount of RAM Type of keyboard Content can be changed to reflect changes in the computer system Page 164

Commonly Used Expansion Cards Graphics cards Sound cards Modem cards Network interface cards (NIC) PC cards (PCMCIA cards) TV tuner cards Graphics cards - connect the system board to the monitor; convert internal electronic signals to video signals Sound cards – convert electronic signals to audio signals and accept audio input from microphones Modem cards – allow distant computers to communicate with each other by converting computer electronic signals to travel over phone lines Network adapter cards (Key Term) (NICs or Network Interface Cards) - connect system unit to a cable (Key Term) attached to a network TV turner cards (Key Term) - PC/TV combination cards led to high audio quality systems called home PCs TV tuner converts video signal for viewing on computer monitor PC cards - credit card-sized expansion cards for portable computers, also known as PCMCIA (Personal Computer Memory Card International Association) cards Page 166

Bus Lines Connect parts of the CPU to each other Data roadway for traveling bits Measured as bus width More lanes, faster traffic Two basic categories System buses Expansion buses Bus lines provide data pathways that connect various system components A bus line is also called a bus (Key Term) It is a pathway for bits representing data and instructions Every computer has two basic categories of buses System – connects the CPU to memory on the system board Expansion – connects the CPU to slots on the system board Page 170

Standard Ports Four common ports Serial ports Parallel ports USB ports FireWire ports Four common ports Serial ports – data transported one bit at a time; mouse, keyboard, modem, etc. Parallel ports – for external devices needing lots of data over short distances, like printers, scanners, external Zip drives USB ports (universal serial bus) – gradually replacing serial and parallel ports; can connect multiple devices; faster than parallel FireWire ports also known as high performance serial bus (HPSB) ports – for high-speed printers and video cameras; as fast as USB 2.0 Two most recent and significant developments in ports and buses: PCI Express (PCIe) (Key Term) – 30 times faster than PCI Contained in many of today’s most powerful microcomputers Serial ATA (SATA) (Key Term) – used to connect both magnetic and optical disk drives to the system board with far greater speed than other buses and slots Return Page 170

Power Supply Computers require direct current (DC) DC power provided by converting alternating current (AC) from wall outlets or batteries Desktop computers use power supply units Notebooks and handhelds use AC adapters Cables are used to connect exterior devices to the system unit via the ports Direct current (DC) powers computers Desktop computers have a power supply unit located within the system unit Notebook computers use AC adapters that are located outside the system unit Page 172