Chapter 4 System Unit Components

The System Unit
The System Unit contains electronic components of the computer used to process data.
There are few components inside the system unit :

• Drive bay(s)
• Power supply
• Sound card
• Video card
• Processor 
• Memory

-The motherboard is the main circuit board of the system unit.

Processor
-The processor known as central processing unit (CPU) interprets and carries out the basic instructions that operate a computer.
-The control unit is the component of the processor that directs and coordinates most of the operations in the computer.
-The arithmetic logic unit (ALU) performs arithmetic, comparison, and other operations.

For every instruction, a processor repeats a set of four basic operations, with comprise a machine cycle.

1. The control unit fetches problem's instructions and data from memory.
2. The control unit decodes the problem's instructions and sends instructions and data to the ALU.
3. The ALU performs a solving for the problem.
4. The results of the problem are solved and stored in memory.

Most current personal computers support pipelining. Processor begins fetching a second instructions before it completes the machine cycle for the first instruction.
The processor contains registers, that temporarily hold data and instructions. The system clock controls the timing of all computer operations.

• A processor chip generates heat that could cause the chip to burn up
• Require additional cooling systems such as Heat sinks, Liquid cooling technology

Parallel processing uses multiple processors simultaneously to execute a single program or task.

Data Representation

• Analog signals are continuous and vary in strength and quality
• Digital signals are in one of two states: on or off

Most computers are digital. The binary system uses two unique digits (0 and 1) [Bits and bytes]

• ASCII (American Standard Code for Information Interchange) is the most widely used coding scheme to represent data.

How a letter is converted to binary form and back

1. A letter is pressed on the keyboard, which in turn creates a special code, called a scan code, for the letter.
2. The scan code for the letter is sent to the system unit.
3. The system unit converts the scan code for the letter to its ASCII binary code and stores it in memory processing.
4. After processing, the binary code for the letter is converted to an image and displayed on the output device.

Memory
Memory consists of electronic components that store instructions waiting to be executed by the processor, data needed by those instructions, and the results of processing the data.
Stores three basic categories of items :

• The operating system and other system software.
• Application programs.
• Data being processed and the resulting information.

Each location in memory has an address. Memory size is measured in kilobytes (KB or K),
megabytes (MB), gigabytes (GB), or terabytes (TB).
The system unit contains two types of memory :

• Volatile memory : - Loses its content when power is turned off (eg : RAM)
• Nonvolatile memory : - does not lose contents when power is removed (eg : ROM, flash memory, and CMOS).

Three basic types of RAM chips exist : Dynamic RAM (DRAM), Static RAM (SRAM), Magnetoresistive RAM (MRAM).
RAMA chips usually reside on a memory module and are inserted into memory slots.