Primary Memory

Table of Contents


Main memory, also known as primary memory or RAM (Random Access Memory), is a crucial component of computer systems. It plays a vital role in the operation of computers by providing fast and temporary storage for actively used data and programs. Understanding primary memory is essential for those interested in computer technology, as it forms the foundation of a computer’s functionality. In this discussion, we will delve into the concept of primary memory, its importance and its key characteristics.

What is primary memory ?

Primary memory refers to a specific section of computer memory that can be directly accessed by the CPU. It offers faster access times compared to secondary memory and is quicker than cache memory within the hierarchy of memories. On average, primary memory has a storage capacity that falls between that of secondary memory (which is larger) and cache memory.
Classification Of Memory
Classification Of Memory

Why do we require primary memory?

 The structure of computer systems aims to minimize access time for processes in order to enhance overall system efficiency. To achieve this reduction in access time for ready processes, the following approach is employed;
  1.  All applications, files and data are stored on secondary storage devices which have larger capacities but longer access times.
  2.  The CPU or processor cannot directly access data from secondary storage; hence it relies on primary memory for efficient processing.
The operating system loads processes into Primary Memory, which is smaller in size and can be directly accessed by the CPU for execution. Only the programs that are loaded in Primary Memory and ready to be executed can be quickly accessed by the CPU, thus enhancing the speed of the system.
Primary Memory can be broadly categorized into two main types; Read Only Memory (ROM) and Random Access Memory (RAM).
Read Only Memory (ROM) is used to store data that doesn’t require any changes. ROM contains programs that run during system startup, such as the bootstrap program that initializes the operating system, as well as essential algorithms needed by the OS. The contents of ROM cannot be altered or modified in any way.

Type of ROM

There are four major types of ROM based on their behavior;
Type Of Rom
Type Of Rom
  1. Masked ROM (MROM); This type of ROM is pre programmed and hardwired, meaning that once the text has been written, it cannot be changed.
  1. Programmable ROM (PROM); Users can only change the content of PROM once. They purchase a blank PROM and write the desired text onto it, but once written, it cannot be altered.
  2. Erasable Programmable ROM (EPROM); This type of ROM can be erased and reprogrammed by removing the original material. UV radiation is used to erase EPROM, allowing for modifications to its content.
The charge stored in the ROM gets discharged when exposed to ultraviolet light, which enables new content to be written on it.
  1. EEPROM : The original data in an electrically erasable and programmable ROM can be altered by selectively erasing specific bytes electrically instead of erasing everything at once. This means that reprogramming an EEPROM takes a considerable amount of time as it needs to be done byte by byte.
 Random Access Memory
Random Access Memory (RAM) is a crucial component in any computer system. It acts as a temporary storage space where the CPU processes instructions for executing system processes. For example, when we click on an application like a browser, the Operating System loads the necessary browser code into RAM before the CPU can execute and open the browser.

Type Of Ram

RAM can be broadly categorized into two types based on their behavior; Static RAM (SRAM) and Dynamic RAM (DRAM).
Ram Memory
Ram Memory
  1. DRAM; Dynamic RAM or DRAM requires regular refreshing every few milliseconds to maintain stored data. It consists of capacitors and transistors, but since capacitors tend to leak electric charge, they need to be recharged periodically. DRAM is commonly used in personal computers and servers due to its lower cost compared to SRAM.
  2. SRAM; Static RAM or SRAM retains data as long as the system remains powered on. Unlike DRAM, SRAM uses sequential circuits like flip flops to store bits, eliminating the need for regular refreshing. However, due to its higher cost, SRAM is primarily utilized when high speed performance is essential.
Now let’s address why Primary Memory (RAM) is considered volatile in nature.
Depending on whether Primary Memory is stored in RAM or ROM, the data it holds may or may not be lost when power is disconnected.
The information in ROM is non volatile, which means it remains intact even if power is lost.
On the other hand, the data stored in RAM is volatile, meaning it disappears when power fails or is disconnected.

Advantages of Primary Memory:

  • Speed: It provides fast data access for the computer’s operations.
  • Responsiveness: It ensures quick program execution and system responsiveness.
  • Random Access: Data can be accessed directly, improving efficiency.

Disadvantages of Primary Memory:

  • Limited Capacity: It has restricted storage compared to secondary storage.
  • Volatility: Data is lost when the computer is turned off.
  • Cost: High-speed primary memory can be expensive to upgrade.
  • Not for Long-Term Storage: It’s unsuitable for storing data permanently.

When cache memory comes into existence?

Cache memory was first introduced in the 1960s. It became an integral part of computer architecture to improve data access speeds by storing frequently used data closer to the CPU.


In conclusion, primary memory is the heart of a computer’s memory hierarchy, serving as a high-speed, volatile storage medium where data and programs are loaded for immediate access by the CPU. Its speed and capacity significantly impact a computer’s performance and responsiveness. While primary memory is crucial for a computer’s operation, it is important to note that it is volatile, meaning its contents are lost when the computer is powered off. Therefore, data and programs must be saved to secondary storage devices like hard drives or SSDs for long-term storage. Primary memory’s role in computing is fundamental, and as technology advances, the capacity and speed of primary memory continue to improve, enabling more powerful and efficient computer systems
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