Primary Storage Devices of Computer – 3 main types

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Primary storage devices are used in computers to work fast. Data is store in primary devices for a short time. When we turn off the computer or any software, data will erase.

This stored data in primary storage devices use during work on the system or in software. It is also known as main memory or internal memory. Main memory direct interacted with the processor or CPU. The processor executes data from the main memory when required. Data is store in a uniform manner in primary storage devices.

In the early days, magnetic drums use as primary storage. Later on, magnetic core memory is use and then semi-conductor memory use for that purpose. And after this, the revolution of RAM comes to that use in modern computers or systems.

Types of Primary storage devices

In general, there are three types of primary storage devices.
1. RAM (random access memory)
2. ROM (Read Only Memory)
3. Cache

Other primary storage devices

But some scholars also include flash memory or registers as primary storage. So in this article, we also briefly describe flash memory and registers but in the last.


RAM is the abbreviation of random access memory. Data will store in RAM temporarily and executed by the CPU when required. It’s located on the motherboard. It is the main memory of the computer. When the computer works, it stores information.

During the working of computer or software. Data save in RAM for the moment. When work end and the system will be off. Data will erase automatically. It is fast memory. Data read and write at the same time.

The working speed of your computer depends upon the memory size of the RAM. Big size memory of RAM, save big data, and at the same time, the working of your computer is fast. RAM sizes are 8GB and 16GB and more according to your work.

We understand this by simple Example.

When we play a game on the computer. Required data store on RAM. So if the size of the memory of RAM is big the gameplay well. Because the data that need during game playing save on RAM fast and execute fast. After the shutdown of the game, the whole data erase from RAM.

Here we discuss the two main types of RAM
1. Static RAM
2. Dynamic RAM

Static RAM

SRAM or Static RAM is the type of RAM. It stores data in its storage in the form of bits. The stored bits in it do not need to be refresh. This data store in a computer till the computer power is on.

SRAM uses flip-flops to store information. The chip used in it has a speed of 10-30ns. SRAM is volatile memory. Static RAM is fast memory. It accesses data easily. It converts and stores data in the form of 0 and 1. SRAM is more expensive than dynamic RAM.

Dynamic RAM

DRAM or Dynamic RAM is a type of RAM. It stores bits of data in the memory cell. The memory cell consists of a transistor and capacitor. It is also the type of semiconductor memory.

Two states of capacitors, charge, and discharge. Shows the two values of capacitor 0 and 1. DRAM is slower than SRAM and it is also cheap. DRAM needs to refresh again and again. When there is a need for low-cost and high-speed memory. DRAM used. RRAM like SRAM is volatile memory.


ROM stands for read-only memory. It is non-volatile memory used in computers. It is the main memory of a computer. ROM built-in memory in computer during manufacturing. Like RAM, it is not easy to access data from it. It stores the starting information and instruction.

ROM is non-volatile memory. The data store in its memory is permanent. When the computer turns off the data erase from it. ROM is use in computers and many other devices. Software and its information store in ROM called firmware.

The working of ROM to store and access data is slow. The information to start computer-like programming is store in it. Basic input & output is also perform using ROM.

There are different types of ROM. Every type of ROM has its own working process. We discuss the working every type of computer here in detail.

Three main types of ROM of primary storage devices

  1. PROM (Programmable read-only memory)
  2. EPROM (Erasable and programmable read-only memory)
  3. EEPROM (Electronic erasable and programmable read-only memory)


In 1956, a Chinese Scientist Chow Wen Tsing invent PROM. PROM stands for Programmable read-only memory. It is a type of ROM. Datastore in it is permanent. It’s used in digital electronic devices which are usually low-level programs.

It is also used in cell phones, medical devices, and other electronic devices. In early computers, PROM work in computers as BIOS. But in modern computers, it changed with EEPROM. PROM manufacture as a blank chip. The data is a program on PROM after the manufacturing.

Data written on PROM once. When data write on PROM, it will not erase forever.


EPROM stands for erasable and programmable random-access memory. It is a type of PROM. It saves data in its memory even computer turns close. EPROM is a non-volatile memory.

Once data write on EPROM memory. Then erased using ultraviolet light. OP-code, address and data are three phases in which the EPROM protocol consists.


EEPROM stands for electronic erasable and programming read-only memory. It is a chip located on the motherboard. EEROM is a non-volatile memory. Because data save in this memory is permanent.

To erase data in memory, EEPROM still required two transistors. Both serial and parallel interfaces use in EEPROM for input and output of data.

EEPROM is also called flash memory.

Flash Memory

As we say at the start of the blog that we discuss flash memory in short. So with EEPROM we also see what is flash memory?

So there is no big difference between both, EEPROM and flash memory. Flash memory is a type of EEPROM. It’s designed for high speed and density. Flash memory is used for firmware.

The two gates NOR and NAND are types of flash memory. But at the circuit level, these two types are different.


Registers are small storage that stores data temporarily. It is part of the CPU. Registers help the CPU to work fast. It’s made CPU speed fast.

There is a different type of memory that is store in CPU registers. We can divide these types into different categories. This division is by working type of registers.

  1. ACC (Accumulator)
  2. MDR (Memory data register)
  3. MAR (Memory address register)
  4. CIR (Current instruction registers)


The accumulator is a type of register. In which arithmetic logical units save. In history, the accumulator is a common term. But in modern computers, many general-purpose registers work.


MDR stands for memory data register. It is a type of register. It stores memory like words data and program data. That is transforming from one place to another.


MAR stands for memory address registers. It is also the type of register. Its works to store the address of that data fetched from the CPU. And the data sent or receive. So, it’s working to store the address of memory.


CTR stands for current instruction register. It is a type of register. It works to store information that is executing currently. The stored information decode step by step. In modern CTR, all work will go parallel.

Cache Memory

Cache memory is fast and efficient data storage. It works between RAM and CPU. It’s located on the motherboard. Cache memory is a temporary storage device. The working of cache memory depends upon its size. If the size of cache memory storage is big. Then more data is store in it and it works fast.

Cache data is also stored in our online browser. When someone visits a particular website the first time. Website store his data in his browser in the form of cache memory.

So when that person accesses that particular website again. The site opens fast and works fast in comparison to the first visit. Because this time site uses his cache data that is store in his browser.

Dear readers, you can also read about primary storage devices from Wikipedia. We can also cover secondary storage devices and the history of storage devices.


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