Inside CPU

CPU, the central processing unit, is basically a microprocessor that can be referred to as the heart of a computer. It's a hardware device built with more than millions of small transistors. It processes every Instruction that has been given to the computer. 

Components of CPU 

1.ALU

2. Control Unit

3. Memory unit

4. Buses

5. Clock

MEMORY UNIT

Registers--

Registers are a sequence of flip-flops connected logically to perform two main functions, i.e. data movement and storing the data. It holds only binary digits since computers can only understand binary language, which is basically on or off. 

It contains two types of registers, special-purpose and general-purpose registers. Generally, the size of the register is 16 bits, but it can vary from 8 to 32 bits.

 Special purpose registers –

MDR or Memory Data registers-

It stores data. Unlike MAR, it does not store addresses. If MDR is an array, then MAR is the index of the array. The bus that connects MDR to the main memory is called a data bus.

MAR or Memory Address registers-

As the name itself suggests, it stores addresses. It holds the addresses of data that is to be accessed. It's like an address log of a particular locality, and if somebody needs anyone's address for delivery purposes or appointments,  etc., then MAR will provide them with that information. The main memory is connected to MAR by the address bus since it stores addresses. 

IR or Instruction register -

The name itself suggests that it has something to do with instructions, and the purpose of a register is to store data, so an IR is a register that stores instructions. 

PC or Program counter - 

Like MAR, it also holds addresses but of the next Instruction for execution. Not the one which is already fetched. 

Accumulator-

This register is used to store data in the middle of the process of execution. It holds intermediate logic values.

General-purpose registers-

These stores data to be executed.

Cache-

It is basically used to make the work done faster, i.e., to load data or Instruction faster on 2nd request. For example, while browsing, you will see that few webpages will take time if you are opening it for the very first time. But once it is opened, the data of that site will be stored in cache memory so that next time the webpage will load faster. It's a temporary storage element.

Computers only understand binary digits, 0s & 1s, so each and every instruction given to the computer is nothing but bits of binary digits. 

Buses

Buses are used for transferring data from one place to another within the digital circuitry. Bus structures are of two types -

1. single bus structure - every component is connected to only one single bus. Transmission of data usually occurs in one clock cycle. Only one component can use the bus at a time. Parallelism is not allowed.
2. multi-bus structure-  multiple buses increase the efficiency and efficacy of data transfer. one can be used to fetched data and the other to fetch instructions in the same clock cycle. It's faster but costly. Most modern processors use multi-bus architecture.

• control bus - a bidirectional bus that carries time signals and other signals from the processor to other components.
• data bus - it is bidirectional and the name itself suggests, it transfers data
• address bus - this bus carries addresses from processor to other components and it is unidirectional.

Control unit

The movement of instructions and every operation that takes place in the CPU is controlled by the control unit, hence controlling the whole computer.