Difference between RAM and HDD

Both RAM and HDD are types of computer memory. RAM is used to store computer programs and data that the CPU needs in real time. RAM data is volatile and is erased once the computer is switched off. HDD, hard disk, has permanent storage and it is used to store userspecific data and operating system files. HDD data is static and remains in the computer even if computer is switched off.

Read this article to find out more about RAM and HDD and how they are different from each other.

What is RAM?

RAM stands for Random Access Memory. RAM is a type of primary memory in computer and other computing devices. RAM is made up of semiconductors, thus it is a type of semiconductor memory. RAM allows the user/CPU to randomly access any part of the data regardless of its position. RAM is a volatile memory which means the data in RAM is dependent on the power supply and as lost when power is switched off.

RAM is classified into two categories− Static RAM (SRAM) and Dynamic RAM (DRAM). SRAM uses transistors and capacitors in its circuit to store data, whereas DRAM uses digital circuit (called flip−flops) to store data in the form of binary digits.

The CPU of a computer can directly access all the cells of RAM. Thus, its read/write speed is very high.

What is HDD?

HDD stands for Hard Disc Drive. In computer systems, HDD is the most widely used secondary storage device. It consists of platter (disks) of non−magnetic material which are coated with a layer of magnetic material. In HDD, the data is stored using magnetic field. For this purpose movable magnetic reader arm is used that can slide over the platters. Hence, HDD is a magnetic memory.

HDDs are very popular in desktops computers and laptops. Since it is a secondary storage device, the CPU cannot directly access data stored in it. But, the data of HDD is first copied into the RAM, and then supplied to the CPU for processing. However, in newer computers and laptops, the HDDs are being replaced by SSDs (Solid State Drives).

Difference between RAM and HDD

All the important differences between RAM and HDD are highlighted in the following table −

Definition RAM stands for Random Access Memory. HDD stands for Hard Disk Drive.
Memory RAM is also called Primary Memory or Main Memory. HDD is also called Secondary Memory.
Component RAM has no moving mechanical parts and consists of transistors etc. HDD contains moving mechanical parts like arm, pin etc.
R/W Time RAM has small read/write or R/W time. HDD has higher read/write time.
Access Every memory area of RAM is accessible at same speed. Different area of HDD may take different time to access.
CPU Access CPU can access data stored on RAM. Data to be copied from ROM to RAM so that CPU can access its data.
Capacity RAM memory is generally smaller than HDD. Now−a−days it ranges from 1GB to 8 GB in desktops. HDD memory is very high. It ranges from 500GB to 4TB in desktops.
Noise RAM don't produces any noise. HDD produces noise due to mechanical movements.
Cost RAM is costly per unit storage. HDD is cheap per unit storage.
Impact on Speed If RAM is low, computer will become slow. HDD has not much impact on computer's speed.


From the above discussion, we can conclude that RAM is a semiconductor-based memory that is used as primary memory, whereas HDD is a magnetic memory used as a secondary storage device in computers. Another important point to be noted about RAM and HDD is that RAM is a volatile memory (data will lost when power is turned off), while HDD is a permanent storage device.