Chapter 4

Chapter 4: System Unit Components

As mentioned in Chapter 1, we have introduced the system unit under components of computer. If you haven't read it yet, the definition of system unit is case that contains the electronic components of the computer used to process data. In this chapter, we will go deeper into the components that can be found in system unit and their function.

Let's start with desktop personal computer system unit, there are:
1) Drive bay(s)
2) Power supply
3) Sound card
4) Video card
5) Processor
6) Memory
And all of these components are integrated into a main circuit board which is called motherboard.

Functions of the components in system unit:
1) Drive bay(s)- a space inside a computer in which a floppy disk, hard disk or disk drive can be accommodated.
2) Expansion slot- a socket on motherboard to hold adapter card.
3) Adapter card- internal expansion card that allows computer to communicate with other peripherals.
4) Sound card- is an adapter card that enable computer to input, process and deliver sound.
5) Video card- is an adapter card that enable computer to input, process and deliver images. It is also called as graphic card.
6) Ports- is the point at which a peripheral attaches to or communicates with a system unit. Also known as jack. For example, keyboard port, mouse port and USB port.
7) Connector- joins a cable to a port.
8) Buses- a communication system that transfer data between components inside a computer, or between computers.
9) Power supply- convert the walls outlet to AC power into DC power. This is to ensure a steady current which will represent digital signal 1,0 and that most electronic components require DC power supply.
10) Memory- any physical device capable of storing information temporarily or permanently.
11) Processor- interpret and carries out basic instructions that operate a computer. Also known as Central Processing Unit (CPU).

  Let's go to how they work, we will start with Processor.
Processor contains a Control Unit (CU) and an Arithmetic Logic Unit (ALU). Both of them work together. CU will direct and coordinate most of the operations in computer whereas ALU performs arithmetic and logical operations. The processor contains registers, that temporarily hold data and instructions. And there is system clock which controls the timing of computer operations. A processor chip will generate heat could cause the chip to burn up that is why additional cooling is required such as heat sinks and liquid cooling technology.

  Relationship between Input device, Output device, Storage device, Memory and Processor:
1) Input device send data to CPU and it will be stored in memory.
2) And processor will begin four basic operations which is called Machine Cycle.
3) First operation is Fetch, CU will fetch the data from memory.
4) Second operation is Decode, CU will decode, check what it means and what to do with the data. And later send to ALU.
5) Third operation is Execute, ALU will take action on the data sent by CU.
6) Fourth operation is Store, ALU will store the result in Memory or Registers.
7) And CU will direct the Memory to release the results to Output device or Storage device.
8) If there is any required program, instructions or data required from Storage device before machine cycle, Storage device will send the data to memory.

Types of Memory:
1) Volatile memory- store data temporarily as it will loses its contents when power is turned off. For example, Random Access Memory (RAM), this is the memory that works together with processor as it is faster than other types of memory. RAM will store the required data and instructions from storage device for each operations when they are in use to provide high speed access. It makes the computer works seamlessly. There are also memory cache which speeds the process of the computer because it stores frequently used instructions and data.
2) Non-Volatile memory- store data permanently and does not lose contents when power is turned off. For example, Read Only Memory (ROM), Flash memory and Complementary Metal-Oxide Semiconductor (CMOS).