The System Unit
• Box-like case that contains computer’s electronic components • Sometimes called the chassis
What are common components inside the system unit?
• Memory module
• Expansion cards
o Sound card
o Modem card
o Video card
o Network interface card
• Ports and Connectors
What is the motherboard?
• Main circuit board in system unit
• Contains chips, integrated circuits, and transistors
• Also called system board
What chip packages are available?
• single edge contact (SEC) cartridge
• dual inline package (DIP)
• flip chip-PGA (FC-PGA) package
• pin grid array (PGA
Central Processing Unit
What is the central processing unit (CPU) ?
• Interprets and carries out basic instructions that operate a computer • Also called the processor
What are the components of the CPU?
• Control Unit
• Arithmetic/Logic Unit (ALU)
What is the control unit?
• Directs and coordinates operations in computer
• Control unit repeats four basic operations:
• Fetch - obtain program instruction or data item from memory • Decode - translate instruction into commands
• Execute - carry out command
• Store - write result to memory
What is a machine cycle?
• Four operations of the CPU comprise a machine cycle
• Also called instruction cycle
• Instruction time (i-time) - time taken to fetch and decode • Execution time (e-time) - time taken to execute and store
An example of a machine cycle
• Student enters math problem (100 x 52) into computer’s memory • Result in memory displays on monitor’s screen
How is the CPU’s speed measured?
• According to how many millions of instructions per second (MIPS) it can process
What are two designs used for the CPU?
• CISC (complex instruction set computing)
o Supports large number of instructions
o CPU executes complex instructions more quickly
• RISC (reduced instruction set computing)
o Supports smaller number of instructions
o CPU executes simple instructions more quickly
What is the arithmetic/logic unit (ALU) ?
• CPU component that performs execution part of the machine cycle o Arithmetic (addition, subtraction, multiplication, and division) o Comparison (greater than, equal to, or less than)
o Logical (AND, OR, NOT)
What is pipelining?
• CPU begins executing second instruction before completing first instruction • Results in faster processing
What is a register?
• Temporary storage area that holds data and instructions o Stores location from where instruction was fetched
o Stores instruction while it is being decoded
o Stores data while ALU processes it
o Stores results of calculation
What is the system clock?
• Synchronizes all computer operations
• Each tick is clock cycle
• MHz megahertz (millions)
• GHz gigahertz (billions)
What is a microprocessor?
• Single processor chip found in personal computers
How do personal computer processors compare?
• Intel - PC
• AMD - PC
• Motorola - Mac
What is a coprocessor?
• Chip that assists processor in performing specific tasks • One type is a floating-point coprocessor, also known as a math or numeric coprocessor
What is parallel processing?
• Using multiple processors simultaneously to execute program faster • Requires special software to divide problem and bring results together
How do computers represent data?
• Most computers are digital
• Recognize only two discrete states: on or off
What is the binary system?
• Number system with two unique digits: 0 and 1
What is a byte?
• Eight bits grouped together
• 256 characters
What are three popular coding systems to represent data?
• ASCII - American Standard Code for Information Interchange • EBCDIC - Extended Binary Coded Decimal...