Updated April 13, 2023
Introduction to CPU Register
In computer architecture, the CPU register holds the key role which is small data holding place or memory, and is an integral part of the processor. It is a very fast memory of computer mainly used to execute the programs and other main operation quite efficiently. Register basically used to quickly store, accept, transfer, and operate on data based on the instructions that will be immediately used by the CPU. In memory hierarchy of a computer registers the top place and is fastest in manipulating the data. Numerous fast multiple ported memory cells are the atomic part of any register.
In basic or simpler microprocessors, a single memory location that is commonly known as an accumulator is present. Basically these registers are used to perform different operations. In a computer, these registers are used by the CPU to perform the operations
Operations of a CPU Register
For CPU processing these register plays a critical role. When we give the input, these are stored and in register processes and the output is from the register only.
So basically a register will perform the following operations.
- Fetch: To fetch the instructions of the user also the instructions that are present in the main memory in a sorted way
- Decode: The second operation is to decode the instructions that need to perform. Thus CPU will be knowing what are the instructions
- Execute: Once the instructions are decoded then execute operation is performed by the CPU. Once done the result is presented on the user screen
Different types of Memory Register
There are various types of the register that are available and some mostly used CPU register are below with the description
- Accumulator (AC)
- Flag Register
- Address Register (AR)
- Data Register (DR)
- Program Counter (PC)
- Instruction Register (IR)
- Stack Control Register (SCR)
- Memory Buffer Register (MBR)
- Index register (IR)
These registers are the most important integral part of the computer and each of these are having a specific purpose. Let us see below
1. Accumulator
Accumulator register is part of ALU which abbreviates to Arithmetic Logical Unit and as the name suggests is responsible for performing arithmetic operations and also in logical operations. The Control unit will store the data values which are fetched from the main memory into the accumulator for the arithmetic or any other logical operations. This register holds the initial data, intermediate results and asl well as the final result of the instruction. The final result of the operations which can be arithmetic or logical will be transferred to the main memory through MBR
2. Flag Register
This register validates or checks upon the various occurrences of a condition in CPU and is handled by this special register called flag register. The size of this register is one or two bytes since it will hold only flag information. This register main gets into the picture when a condition is being operated.
3. Data Register
This register is used to temporarily store the data being transmitted from the other involved peripheral devices.
4. Address register
This address the register also called memory address register MAR is a memory unit that stores the address location od data or instructions on the main memory. They contain a portion of the address which can be used to compute the complete address.
5. Program Counter
This register is also known popularly as an instruction pointer register. This register as the name suggests will be holding the address of the next instruction that needs to be fetched and executed or performed. When the instruction is fetched then the value is incremented and hence will always be holding the address of the next instruction to be run.
6. Instruction Register
Once the instruction is fetched from the main memory it is stored in Instruction Register IR. The control units take the instructions from here decodes it and executes it by sending the required signals to the required component.
7. Stack Control Register SCR
As the work stack in the name of this register represents block, here it represents a set of memory blocks where the data is stored in and as well as fetched. FILO which is First IN and Last Out will be followed for the storing and retrieval of the data.
8. Memory Buffer Register
This register holds the information or the data which is read from or written in the memory. The content or the instructions stored in this register will be transferred to Instruction Register IR whereas the content of the data is transferred to the accumulator or I/O register.
9. Index Register
The index register is an integral part of computer CPU which will help in modifying the address of the memory operand during the execution of the program. Basically the contents of the index register are added to the immediate address to get the resultant the effective address of data or instruction on the memory.
Why we need a CPU register?
For the fast operations of an instruction, the CPU register is highly useful. Without theses CPU operation is unimaginable. These are the fastest memory when we look at the different memory and Laos will hold the top position in the memory hierarchy. A register can hold an instruction, address, or any other sort of data. There are different types of registers available and we have seen most used in the above part of the article. Thus having register, it makes the operations of CPU smooth efficient and meaningfull. A register must be large enough according to ist requirements and specifications.
Advantages and Disadvantages
Below are advantages and disadvantages
Advantages
Below are the advantages:
- These are fastest memory blocks and hence instructions are executed fastly compared to main memory
- Since each register purpose is different, and instructions will be handled with grace and smoothness by the CPU with the help of registers
- There are rarely any CPU that will not be having register in the digital world
Disadvantages
Let us take a look at the disadvantages:
- Since the memory size of the register is finite and if the instruction is bigger then cpu need to use cache or main memory along with register for the operation
Conclusion
Thus the number of the register that is available in the CPU and how large is our instructions will be significantly impacting the time of execution of our code. This having adequate CPU register will help in faster and smooth execution
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