The central processing unit (CPU)
It is another computer sub unit under the unit called hardware,it is also called processor or sometimes regarded as the brain of a computer since all processing activities are carried out inside it.
It is mounted on the circuit board inside the system unit called mother board/ system board.
There are three major functional components/elements of this sub unit namely:
- control unit (CU)
- Arithmetic and logic unit (ALU)
- main memory.
- Control unit
coordinates all processing activities in the CPU as well as input/ output operations. This is made possible by use of system clock which sends electrical signals as its means of communication between activities and resources. The numbers of pulses per second determine the speed of CPU.
- Arithmetic and logic unit
is a unit of the in which all arithmetic and logical operations are carried out. Arithmetic operations include: addition, subtraction, multiplication, division where as logical operations are based on the ability of the computer to compare two or more values. They include: greater than (>) less than (<) equal to (=) and not equal to. ALU process data by help of special temporal storage locations called register which hold data just before processing and after processing.
- Main memory
is also known as primary storage since it is directly accessed by the processor. This memory can be classified into: Read Only Memory (ROM) and Random Access Memory (RAM).
store programmed instructions that remain unchanged permanently/ semi permanently depending with the type of ROM. The four types of ROM include:
- Mask Read Only Memory.
- Erasable Programmable Read Only Memory.
- Programmable Read Only Memory.
- Electrically Erasable Programmable Read Only Memory.
is also called working memory because it holds data needed by the currently running application.
Since its content is accessed irrespective of the sequence that was used during storage, it is then referred to as Random Memory. The types of RAM are Static RAM.
Storage capacity of computers is measured in a special unit named byte. This is equivalent to one character. A character can be a letter, number or special symbol (space inclusive). 1byte – 8 bits, 1kiloByte (Kb)– 1000 bytes, 1megabyte (Mb)– 1million bytes, 1Giga byte (Gb)- 1billion bytes, 1terabyte(Tb)- 1trillion bytes
Special purpose memories.
These are minute memories included in the microprocessor to enhance it’s speed. They include buffers found in input output devices and Registers found inside the CPU
Examples of registers include
- Accumulators hold the last processing step of ALU.
- Storage register temporarily holds a piece of data that is on its way to and fro the CPU and main memory.
- Instruction register temporarily holds an instruction just before it is interpreted.
- Address register temporarily holds the next piece of data waiting to be processed.