Introduction to Registers

3. Internal Registers

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  Instruction Register (IR): It holds the current instruction that is executed currently. This instruction would have been fetched from the main memory. Its size is 16 bit. CPU, as instructed by the control unit, will execute this instruction after decoding.
  
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  Memory Buffer Register (MBR): It holds the content of the memory that is transferred between the main memory and another component in both the direction and it is two-way registers.
  
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  Memory Address Registers (MAR): It stores the address of the memory from where the data will have to be fetched to the CPU for processing.
  

4. Other Registers

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  Architectural: Defined by Architecture are visible to software and it is pseudo registers.
  
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  Hardware: These are not part of the CPU and they are present outside.
  

Importance of Registers

It plays a critical role in storing instructions, addresses, data, and results in tiny quickly retrievable memory units and enhance the program execution speed. Though each has a specific function to perform, they are easily accessible to CPU, Memory and other components of computers and the storing contents into and out of these registers are pretty fast.
Advantages:

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  It provides faster access to data, instruction, and addresses stored in it for CPU.
  
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  It handles the storing/retrieving variables accessed repeatedly.
  
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  It helps in enhancing program performance significantly.
  
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  Optimized utilization of memory while executing the program.
  

Types of Register in Computer Organization

In Computer Organisation, the register is utilized to acknowledge, store, move information and directions that are being utilized quickly by the CPU. There are different kinds of registers utilized for different reasons. Some of the commonly used registers are:

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  AC ( accumulator )
  
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  DR ( Data registers )
  
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  AR ( Address registers )
  
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  PC ( Program counter )
  
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  MDR ( Memory data registers )
  
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  IR ( index registers )
  
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  MBR ( Memory buffer registers )
  

These registers are utilized for playing out the different operations. When we perform some operations, the CPU utilizes these registers to perform the operations. When we provide input to the system for a certain operation, the provided information or the input gets stored in the registers. Once the ALU arithmetic and logical unit process the output, the processed data is again provided to us by the registers.
The sole reason for having a register is the quick recovery of information that the CPU will later process. The CPU can use RAM over the hard disk to retrieve the memory, which is comparatively a much faster option, but the speed retrieved from RAM is still not enough. Therefore, we have catch memory, which is faster than registers. These registers work with CPU memory like catch and RAM to complete the task quickly.

Operation Performed by Registers

Following major operations performed by registers, such as:

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  Fetch: The fetch operation is utilized for taking the directions by the client. The instructions that are stored away into the main memory for later processing are fetched by registers.
  
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  Decode: This operation is utilized for deciphering the instructions implies the instructions are decoded the CPU will discover which operation is to be performed on the instructions.
  
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