Classification of Memory

Table of Contents


Computer systems heavily rely on memory as a crucial component for their proper functioning. Memory is divided into different categories based on its purpose and usage. In this section, we will delve into a detailed exploration of memory classification. We will also discuss various types of memory, their features, such as RAM, ROM, SRAM, DRAM and weigh their advantages and disadvantages.

What is computer memory?

Computer memory refers to any physical device utilized to temporarily or permanently store data, information or instructions. It comprises storage units that hold binary information in the form of bits. The memory is divided into smaller components called cells, each with a unique address used to store data within the memory range from zero to one less than the size of the memory. For instance, if the computer’s memory size is 64k words, there would be 64 * 1024 = 65536 locations or cells available. The addresses of these cells range from 0 to 65535.

Why do we require computer memory?

 In a computer system context, we need it to store diverse types of data such as text documents, images video files audio files etc., which can be retrieved whenever necessary.
As an illustration, when we write and run a computer program, it is first stored in the primary memory. In case the processor does not require specific items for an extended period, the program or data gets automatically saved into the permanent or secondary memory. Afterwards, the data is retrieved from secondary memory to the main memory and carries out the execution of codes.

Classification of Memory

Classification Of Memory
Classification Of Memory

Primary or Main Memory

Primary memory, also known as the main memory of a computer system, is responsible for direct communication between the CPU, auxiliary memory and cache memory. Its purpose is to store programs and data while the processor is actively using them. When a program or data needs to be executed, the processor first loads instructions or programs from secondary memory into the main memory before starting execution. Accessing or executing data from primary memory is faster due to its cache or register memory, which provides a quicker response time and its proximity to the CPU. 
The primary memory can be further divided into two parts;
  1. RAM (Random Access Memory); RAM is a type of main memory that allows for direct access by the CPU. It serves as temporary storage for data, programs or program results in a computer device. It facilitates reading and writing operations in memory while the machine operates.
Overall, primary memory plays a vital role in facilitating efficient communication between various components of a computer system and ensuring smooth execution of programs and tasks.
RAM or random access memory, is a type of computer memory that is considered volatile. This means that if there is a power failure or the computer is turned off, any information stored in RAM will be lost. Additionally, RAM allows for the random reading and accessing of data stored within it. There are two main types of RAM; SRAM and DRAM.
DRAM, short for Dynamic Random Access Memory, is a type of RAM that is used for storing data in a dynamic manner. Each cell in DRAM holds one bit of information and consists of a capacitor and a transistor. Due to their small sizes, millions of these cells can be stored on a single chip, allowing DRAM chips to hold more data compared to SRAM chips of the same size. However, to maintain the stored information, the capacitor in DRAM needs continuous refreshing as it is volatile. If power is switched off, the data stored in memory will be lost.
  1. ROM (Read Only Memory); ROM refers to another component of primary memory that stores permanent instructions or data that cannot be modified by normal computer operations.

Types of ROM

Moving on to Read Only Memory (ROM), there are five types worth mentioning;
1) MROM; This is the oldest type where the program or data is preconfigured by the integrated circuit manufacturer during manufacturing. Users cannot change the program or instructions stored in MROM chips.
2) PROM (Programmable Read Only Memory); This digital read only memory allows users to write information or programs only once.
It refers to an empty PROM chip where users have the ability to write their desired content or program just once using a special PROM programmer or PROM burner device. After that, the data or instructions cannot be altered or erased.
3) EPROM (Erasable and Programmable Read Only Memory):
EPROM (Erasable and Programmable Read Only Memory) is a type of read only memory where stored data can be erased and reprogrammed just once in the EPROM memory. It is a non volatile memory chip that retains data even without power supply and can store information for a minimum of 10 to 20 years.
4) EEPROM (Electrically Erasable and Programmable Read Only Memory);
The EEPROM is a type of memory that allows for data erasure and reprogramming using a high voltage electrical charge. It serves as a non volatile memory, meaning the stored data remains intact even when the power is turned off. In EEPROM, data can be erased and reprogrammed multiple times, up to 10 thousand times, with each byte being erased individually.
5) Flash ROM;
Flash memory is a form of non volatile storage chip that can be written or programmed in small units called blocks or sectors. Similar to EEPROM, flash memory retains its contents even when the power source is turned off. It is commonly used for transferring data between computers and digital devices.

Secondary Memory

Secondary memory, also referred to as external memory, serves as a long term storage space for a vast amount of data. It encompasses various storage media like hard drives, USBs, CDs, flash drives and DVDs. Unlike primary memory, secondary memory is not directly accessible by the CPU. Instead, the data from secondary memory is first loaded into Random Access Memory (RAM) and then processed by the CPU for reading or updating. Secondary memory devices include magnetic disks (hard disks and floppy disks), optical disks (CDs and CDROMs) and magnetic tapes.

Characteristics of Secondary Memory;

  1. It operates at a slower speed compared to primary/main memory.
  2. Data stored in secondary memory is non volatile and remains intact even when power is turned off.
  3. It can store various types of data such as audio, video, images, text documents, software programs, etc.
  4. The stored data in secondary memory is permanent; it does not get lost when power is interrupted.
  5. Different types of optical and magnetic memories are used for storing data.

Types of Secondary Memory

Hard disk

The hard disk is a storage component in a computer that retains data, programs and files permanently. It doesn’t lose any stored information when the computer’s power is turned off.
Typically, the internal storage component of a computer is located on the motherboard. It uses one or more rigid, fast rotating disk platters enclosed in an air sealed casing to store and retrieve data. This large storage device can be found in every computer or laptop and is used for permanently storing installed software, music, text documentation, videos, operating systems and user data until it is intentionally deleted.
Hard Disk
Hard Disk

Floppy Disk

A floppy disk is a type of secondary storage system that consists of thin, flexible magnetic coated disks used for storing electronic data like computer files. It is also known as a Floppy Diskette and comes in three different sizes; 8 inches, 5.5 inches and 3.5 inches. The stored data on a floppy disk can be accessed using a floppy disk drive. Additionally, this drive is essential for installing new programs on a computer or creating backups of important information. Although it’s the oldest form of portable storage device available, it has limited capacity and can only store up to 1.44 MB of data. As most programs grew larger in size over time, multiple floppy disks were often required to store substantial amounts of data.
Floppy Disk
Floppy Disk

CD (Compact Disc)

A CD stands for Compact Disc and serves as an optical disk storage deviceA storage device is utilized to keep different types of data such as audio, videos, files, operating systems, backup files and any other valuable information for a computer. The CD has a thickness of 1.2 mm and a height of 12 cm, which can hold around 783 MB of data. It employs laser light to both read and write data on CDs.
Cd (Compact Disc)
Cd (Compact Disc)


To sum up, it is essential to grasp the concept of memory classification in computer fundamentals in order to understand how data is stored and accessed by computers. Different types of memory, such as the temporary and fast RAM or the more permanent storage like hard drives, serve specific functions. The classification allows us to appreciate the trade off between speed and capacity in computer operations, ensuring efficient handling and retrieval of data. Recognizing the importance of memory classification helps us gain a better understanding of how computers function and the underlying storage mechanisms that support their operations.
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