Difference Between Memory and Registers

In this article, we will discuss the difference between memory and registers. Both of these increase the processor’s working speed. The processor’s speed can increase by increasing the registers in the CPU or by using registers of high bit capacity. Similarly, increasing the actual main memory of the computer can cause the CPU to process faster. We call this memory Random Access Memory (RAM) or primary memory.

Although both of these can increase a processor’s speed, they have differences in their actual working. Register holds the program that the CPU is processing, whereas main memory (RAM) holds the data or instructions that the CPU requires for the execution of a program.

The complete definition and details of both memory and registers are given below:

Memory Introduction 

Computer memory is a kind of computer storage space or device that stores data temporarily. It is categorized into two types:

  • Primary/Main Memory
  • Secondary/Permanent Memory

Primary Memory

Main memory is placed inside the CPU and is usually called RAM. We also call it volatile or temporary storage. Volatile storage is a kind of memory whose contents wipe off when the power supply to the system cuts off. Or, in other words, its contents are only available if the power of the system is on, and whenever the supply is off, the contents no longer remain. This is until or unless they are explicitly stored in external or internal secondary storage. The CPU takes less time to retrieve the data from the RAM in comparison to secondary storage or permanent storage.

RAM stores the data that the CPU needs during the execution of a program. If the data that the CPU needs for the execution of the program is not present in the RAM, the system fetches it from the secondary memory into the RAM. After fetching the data from the secondary memory into the RAM, it remains there until the new data replaces it or the power supply is cut off.

As the main memory is inside the computer, we also refer to it as internal storage. Being placed closer to the processor or CPU is the actual reason that it takes less time to send the data or instructions from the RAM to the CPU for execution of a program in comparison to secondary memory.

Today, RAM may range from 1GB to 16GB of storage. As much as the storage of the primary memory (RAM) increases, the processing speed of the processor (CPU) will also increase accordingly.

Secondary Memory:

Secondary memory is a type of hardware device that stores data permanently. We also refer to it as non-volatile storage. Non-volatile means that the contents of secondary memory are not lost if the electricity supply is lost.

Secondary memory can actually be categorized as internal or external secondary storage. Internal secondary storage is usually a hard drive or ROM (Read Only Memory). Whereas the external secondary storage may include a USB flash drive or CD (Compact Disk).

Nowadays, the capacity of secondary storage may range from several gigabytes (GBs) to terabytes (TBs).

The fetching of data from secondary storage to the CPU for processing takes more time than retrieving data from main memory. Hence, usually, the execution of programs that require data from internal or external secondary storage devices slows down the processing. Secondary memory never holds the data being processed. It only stores data, and when that stored data is required for the execution of any program, it is fetched into the main memory.

ROM has many other types as well. Some ROMs are programmed by the manufacturer, and the programmed data cannot be deleted or altered as it contains some permanent instructions or programs for the system, such as booting the system, etc. Other types of ROMs are re-programmable, which means their data can be altered, deleted, or rewritten in electronic or magnetic ways.

Registers Introduction 

Registers are storage area elements that are built inside the CPU and keep holding the data temporarily. These only hold the program or instructions that the CPU is executing. Data and instructions from the register are directly accessible by the CPU or processor. Retrieval of data from registers is faster in comparison to main memory, and therefore registers increase the speed of the processor. The CPU decodes the instructions or program and executes them at the rate of more than one operation per CPU or processor cycle.

Unlike main memory, registers are controllable. The user of the computer may store or retrieve the information or data from the registers.

We measure the register in terms of bits. For example, a CPU can have registers of sizes 16-bit, 32-bit, or 64-bit. The greater the bit capacity of the CPU, the greater the speed of CPU processing.

Types of Registers

There are several types of registers. Some of the registers are described as follows:

Data Register (DR)

The data register has a capacity of 16 bits. It keeps holding the operands on which the CPU needs to perform the operations.

Address Register (AR)

The address register has a capacity of 12 bits. It keeps holding the address of a memory location.

Accumulator Register (AC)

The Accumulator Register is a 16-bit register. It collects the results of CPU operations after processing.

Instruction Register (IR)

It is also a 16-bit register. It keeps holding the current instruction that the CPU is processing or executing.

Program Counter Register (PC)

The program counter register is a 12-bit register. It keeps holding the address of the next instruction that the CPU needs to fetch and execute.

Comparison Chart

DefinitionIt holds the instructions or program that the processor is executing.It holds the data and instructions that the processor requires for the execution of a program.
Speed of fetching of dataThe registers fetch data more quickly in comparison to memory.The fetching of data from memory takes more time in comparison to registers.
LocationRegisters are placed inside the processor of the computer.Main memory is present outside the CPU but is closer to it.
MeasurementThe measurement of registers is in bits.Memory capacity measurement is in kilobytes (KBs) or gigabytes (GBs).
CapacityA CPU can have a register capacity of 16 bits, 32 bits, or 64 bits built into it, which also determines its speed.Memory today may range from gigabytes (GBs) to kilobytes (KBs).
Types/ExamplesData Register (DR)

Address Register (AR)Accumulator Register (AC)Instruction Register (IR)Program Counter Register (PC)

Main memory, orRAM,M of the computer.
Data holdingRegisters are small storage elements. Therefore, they hold less data in comparison to memory.Memory has more storage capacity than registers; therefore, it can hold more data in comparison to registers.
Control of the UserRegisters are controllable. The user may store or retrieve data or information from registers.Memory is completely uncontrollable.
Access rate of CPUThe CPU executes more than one instruction from the register in one CPU/processor cycle.The rate of data retrieval by the CPU from memory is slower in comparison to registers.


In short words, registers keep holding the instructions that the CPU is processing, while main memory (RAM) keeps holding the data or instructions that the CPU requires. Fetching data from the register is faster in comparison to fetching data from RAM. Registers can hold less data at a time in comparison to RAM. The CPU operates on the contents of the registers more than once in a CPU/processor cycle. While retrieval of data from the RAM is much slower than in the case of a register.

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