Chapter 4: The Components of the System Unit

By Pramila devi

What is the system unit?Case that contain the motherboard, the flat

board within the personal computer housing that holds the chips and circuitry that organize the computers activities.

Sometimes called chassis, is made of metal or plastic and protects the internal electronic components from damage.

The electronic components and circuitry of the system unit, such as the processor and memory, usually are part of or are connected to a circuit board called the motherboard.

What is the motherboard?Sometimes called a system board, is the main circuit

board of the system unit.The motherboard contains several bus lines, or buses,

sets of parallel electrical paths that transport electrical signals. The system bus transfers data between CPU and memory. Bus width and speed affect system performance.

Some expansion buses connect to expansion slots on the motherboard and can receive expansion boards (also called interface cards or adapter cards) that enable you to connect various peripheral devices to the computer.

A serial port enables data to be transmitted one bit at a time, while a parallel port transmit a group of bits at a time.

What is the Central Processing Unit (CPU)? A CPU, or processor, on a chip is a microprocessor.A microprocessor maybe called a logic chip when it is

used to control specialized devices.A microprocessor contains tiny transistors, electronic

switches that may or may not allow current to pass through, representing a 1 or 0 bit, respectively.

The more functions that are combined on a microprocessor, the faster the computer runs, the cheaper it is to make, and the more reliable it is.

The 2 parts of the CPU are the control unit and the arithmetic logic unit, both working together as a team to process the computer’s command.

What is the machine cycle?Four operation of CPU comprise a machine

cycle

memory

Step 1. FETCH obtain program instruction or data item from memory

Step 2.DECODETranslate instructionInto commands

Control unitALU Step 3.EXECUTECarry out command

Processor

Step 4. STOREWrite result to memory

What is memory?Electronic components that store instruction,

data, and result.Consist of one or more chips on motherboard

or other circuit board.Each byte stored in unique location called an

address, similar to seats in a concert hall.

What is Random Access Memory(RAM)?Keeps the instruction and data for whatever

programs you are using at the moment.Divided into two types: static

RAM(SRAM),which is faster, and dynamic RAM(DRAM), which is slower and much less expensive, SDRAM and RDRAM are faster and more expensive types of DRAM.