THE CENTRAL PROCESSING UNIT (C.P.U) 1_SS 2NOTES

 THE CENTRAL PROCESSING UNIT (C.P.U) 1

Meaning and Components of the CPU - Control Unit (CU) - Arithmetic Logic Unit (ALU) - and Registers

Meaning of Central Processing Unit (CPU)

The Central Processing Unit (CPU) is the computer component that's responsible for interpreting and executing most of the commands from the computer's other hardware and software.

All sorts of devices use a CPU, including desktop, laptop, tablet computers, and smartphones...even your flat-screen television set.

Intel and AMD are the two most popular CPU manufacturers for desktops, laptops, and servers, while NVIDIA and Qualcomm are big smartphone and tablet CPU makers.

CPU has different names including processor, microprocessor or the “brain of the computer”.

A modern CPU is usually small and square, with short, rounded, metallic connectors on its underside. Some have pins instead of metallic connectors.

The CPU attaches directly to a CPU ‘socket’ (or sometimes a ‘slot’) on the motherboard. The CPU is inserted into the socket pin-side-down.

The clock speed of a processor is the number of instructions it can process in any given second, measured in hertz (Hz). A CPU with a clock speed of 3.0 GHz can process 3 billion instructions each /per second.

Some devices have a single-core processor while others may have a dual-core (or quad-core, etc.) processor.

Components of the CPU

The components of the CPU work together to achieve its functions. The three components are:

1.      Arithmetic Logic Unit

2.      Control Unit

3.      Registers

Functions of Arithmetic Logic Unit (ALU)

·         Executes all arithmetic operations such as ADD, SUBTRACT, DIVIDE etc.

·         Executes logical operations (i.e. making comparison) such as AND, OR, XOR etc.

Functions of Control Unit (CU)

·         It directs the flow of data and information in the computer.

·         It oversees the operation of the input and output (I/O) devices.

·         Interprets instructions

Meaning of Registers

Registers are temporary storage location used to quickly accept, store, and transfer data and instructions that are being used immediately by the CPU. They are special purpose memory which resides within the CPU.

Types of Registers

• AC ( accumulator )
• DR ( Data registers )
• MAR ( Address registers )
• PC ( Program counter )
• MDR ( Memory data registers )
• IR ( index registers )
• MBR ( Memory buffer registers )
• Current Instruction Register (CIR)
• AC ( accumulator ) : This is a type of register for short-term, intermediate storage of arithmetic and logic data in a computer's central processing unit (CPU).
• Data registers (DR):  is used to hold data that will be stored or fetched from the computer memory, also known as random-access memory (RAM).
• Program counter (PC): is a register in a computer processor that contains the address (location) of the instruction being executed at the current time.
• Memory data registers (MDR): This holds data that is being transferred to or from memory.
•  Index Registers (IR):  holds the current offset of a memory location, with another register holding the base address, so the combination of the two registers creates a completed memory address.
• Memory buffer registers (MBR) : is the register in a computer's CPU that stores the data being transferred to and from the immediate access storage.
• Current Instruction Register (CIR): This contains the current instruction during processing. It holds the current instruction to be executed.

    DIFFERENCES BETWEEN REGISTERS AND MAIN MEMORY

. No.	Register	Main Memory
	1. Registers hold operands or  instructions that CPU would be currently processing.	Memory holds instructions and the data about the currently executing program required by the CPU.
	2. They contain small amounts  of data− 32bits to 64bits.	Memory can range from some GB (Giga bytes) to TB (Tera bytes).
	3. CPU can operate on the contents  of the register at the  rate of more than one operation during one clock cycle.	The CPU accesses memory at a slower rate in comparison to memory access in a register.
	4. There are many types of  registers− Accumulator register, Program counter, Instruction register, Address register.	There are different types of memory− RAM, ROM.
	5. They can be controlled, i.e.  information can be stored and  retrieved from them.	The memory can’t be controlled.
	6. It is quick in comparison to memory.	RAM is slow in comparison to registers.

Class Activities

1. Explain the concept of the CPU

2. List any three (3) components of the CPU and explain any two (2) from the aforementioned.

3. What are registers and explain any two (2) types of registers.

4a. MDR stands for ______________________

  b. CIR stands for  _______________________