C/IL 102 Computer and Information Literacy
Spring 1998
CHAPTER 3
THE SYSTEM UNIT
PRIMARY OBJECTIVES
 Define a bit and a byte
 Describe data representation
 Identify the components of the system unit
 Describe the four steps machine cycle
 Describe RAM and ROM
 Explain parallel and serial ports
 Describe a machine language instruction
 Explain how computers use the binary number system
WHAT IS THE SYSTEM UNIT?
 System unit
 CPU
 Memory
 Other electronics
 Connects to peripherals
 Input devices (mouse, keyboard)
 Output devices (monitor, printer)
 Storage devices (disk drives)
HOW DATA IS REPRESENTED IN A COMPUTER
 Bit - the smallest unit of data handled by a computer (short for binary digit)
 Byte - a group of 8 bits
 ASCII (American Standard Code for Information Interchange)- one byte for each letter.
 EBCDIC (Extended Binary Coded Decimal Interchange Code) )- one byte for each letter.
 Unicode - two bytes for each letter.
THE COMPONENTS OF THE SYSTEM UNIT
 The components of the system unit are usually contained in a metal or plastic case. The components include
the motherboard, the microprocessor and CPU, upgrade sockets, memory, coprocessors, buses, expansion
slots, ports and connectors, bays, the power supply, and sound components.
MOTHERBOARD
 A circuit board that contains most of the electronic components of the system unit
MICROPROCESSOR AND THE CPU
 Microprocessor
 Integrated circuit (IC)
 Central processing unit (CPU)
 The control unit
 Machine cycle
 Fetching + Decoding + Executing + Storing
 Arithmetic/logic unit (ALU)
 Arithmetic operations + Logical operations
 Registers
 System clock: Synchronize all computer operations
 Megahertz
 Word Size: the # of bits that the CPU can process at one time
 8-bit, 16-bit, 32-bit or 64-bit word sizes
 Microprocessor Comparison
 Widely used microprocessors
COPROCESSORS
 Math coprocessors-- some coprocessors designed into the CPU
MEMORY
 Integrated circuits that temporarily store program instructions and data that can be retrieved
C/IL 102 Computer and Information Literacy
 Memory address
 Size
 Kilobyte (K or KB) = 1,024 bytes
 Megabyte (MB) = 1 thousand kilobytes
 Gigabyte (GB) = 1 million kilobytes
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COMMON MEMORY TYPES
 RAM (random access memory)
 Volatile
 Flash RAM
 SIMMs and DIMMs
 Cache
 Level 1 (L1) - internal cache on the chip itself
 Level 2 (L2) - cache on the motherboard or the CPU
 ROM (read only memory)
 Stores information or instructions that do not change
 nonvolatile
 Instructions stored here are called firmware or microcode
 CMOS (complementary metal-oxide semiconductor)
 Stores information about the system, such as amount of RAM and the keyboard type
 Used when the computer starts up
 Battery powered
 MEMORY SPEED
 Access time -- The time needed to find and retrieve data
 Dynamic RAM (DRAM) -- 50 - 100 ns (Nanoseconds -- one billionth of a second)
 Static RAM (SRAM) -- 10-50 ns
BUSES
 Path along which bits are transmitted
 Local bus -- connected to the CPU directly
 Expansion bus -- connected to the memory
EXPANSION SLOTS
 Expansion card
 Expansion board/Controller card/Adapter card/Interface card
 PC Card
 PCMCIA cards (Personal Computer Memory Card International Association)
PORTS AND CONNECTORS
 Used to connect the system unit to peripheral devices, such as printers and modems
 Connectors
 Male + Female
 Parallel ports
 Printers / Disk and tape drives / SCSI (small computer system interface)
 Serial ports
 Mouse / Keyboard / MIDI
MACHINE LANGUAGE INSTRUCTIONS
 Instruction set
 Instruction = Operation code + Operands
 MIPS: Million instructions per second
 Floating point operations
 Megaflops (MFLOPS) / Gigaflops (GFLOPS)
NUMBER SYSTEMS
 Decimal number system
 Base 10 number system
Spring 1998
C/IL 102 Computer and Information Literacy
 Binary number system
 Base 2 number system
 Hexadecimal number system
 Base 16 number system
 Converting ASCII to hexadecimal
Spring 1998