Question

The Central Processing Unit consist of three main units. List these three units and discuss the functionality of each.

Answer 1

CPU (Central Processing Unit) consists of three main units.

1. Memory or Storage Unit
2. Control Unit
3. ALU(Arithmetic Logic Unit)

1) Memory or Storage Unit

Memory is a collection of storage registers used to transfer information in and out of the unit. It can store instructions, data, and intermediate results. it can provide information when it is needed. The information stored in the memory as binary code in
groups of bits called word. The binary is two logic levels logic 1 and logic 0 .Bit: is binary digit (1) or (0), and Byte: is a group of eight bits.
Memory in general is divided into two general categories:

• Primary Memory
• Secondary Memory

primary memory: The primary memory is also known as internal memory. It is the types of computer memories that are directly accessed by the processor using data bus are called primary memory. That allows a processor to access stores running programs and currently processed data.These memories are limited in capacity and manufactured by using integrated circuits (IC) or semiconductor device. Its speed of Data accessing is faster than secondary memory. It is more expensive than secondary memory.

Types of Primary Memory

• RAM (Random Access Memory) : It is an high speed memory and its volatile, it means RAM can't store permanent data. different types of RAM are, Static Random Access Memory (SRAM), Dynamic Random Access Memory (DRAM) .
• ROM (Read Only Memory) : The memory from which we can only read but cannot write on it. This type of memory is non-volatile. The information is stored permanently in such memories during manufacture. A ROM stores such instructions that are required to start a computer. This operation is referred to as bootstrap.

secondary memory : This type of memory is also known as external memory or non-volatile. It is slower than the main memory. These are used for storing data/information permanently. For example, disk, CD-ROM, DVD, etc.

2) Control Unit

A control unit or CU is circuitry that directs operations within a computer's processor. CU functions are as follows:

• Controls sequential instruction execution.
• Interprets instructions.
• Guides data flow through different computer areas.
• Regulates and controls processor timing.
• Sends and receives control signals from other computer devices.
• Handles multiple tasks, such as fetching, decoding, execution handling and storing results.

Control Units are designed of two types. they are,Hardwired control and Microprogram control.

The Hardwired control is based on a fixed architecture and made up of flip-flops, logic gates, digital circuits and encoder and decoder circuits that are wired in a specific and fixed way. When instruction set changes are required. but in the case of Microprogram control programs stored in a special control memory and are based on flowcharts. They are replaceable and ideal because of their simplicity.

3) ALU(Arithmetic Logic Unit)

An ALU is an integrated circuit within a CPU or GPU that performs arithmetic and logic operations. Arithmetic instructions include addition, subtraction, Although multiplication and division are sometimes used, these operations are more expensive to make. Addition can be used to substitute for multiplication and subtraction for division.and shifting operations, while logic instructions include boolean comparisons, such as AND, OR, XOR, and NOT operations.