Difference Between Hard Disk and RAM

Hard Disk vs RAM

RAM and Hard disk Drive are two types of memory used in computers. They both are important and serve different functions within the system. HDD or the Hard Disk Drive stores information for permanent storage and RAM stores information for relatively short term usage by the processors and other components such as the VGA.

Not only they belong to two different classes of memory devices, but also their structure, performance, and capacities are completely different from one other.

Hard Disk Drive (HDD) / Hard Drive

A hard disk drive (HDD) is a secondary data storage device used for storing and retrieving digital information in a computer. Introduced by IBM in 1956, hard disk drive was the dominant secondary storage device for general purpose computers by the early 1960s and still is the dominant form of storage. The technology has improved significantly since its introduction.

A hard disk drive consists of following components.

1. Logic Board – the controller circuit board of the HDD, it communicates with the processor and controls the relevant components of the HDD drive.

2. Actuator, Voice coil and Motor Assembly – controls and drives the arm holding the sensors used to write and read the information.

3. Actuator Arms – long and triangular in shaped metal parts with the base being attached to the actuator, it is the main structure supporting the read-write heads.

4. Sliders – fixed to the tip of the actuator arm, and carry the read write heads across the disks.

5. Read/Write Heads – write and read the information from the magnetic disks.

6. Spindle and the Spindle Motor – the central assembly of the disks and the motor driving the disks

7. Hard Disks – discussed below

The hard drives are prominent due to their capacity and performance. The capacity of the HDDs varies from drive to another but has been consistently increasing over the time. In general, a modern PC uses a HDD with capacity in TeraByte ranges. For computers in specific tasks such as data centers use hard drives with much higher capacity.

The performance of the hard drive is characterized by the Access Time, Rotational Delay, and Transfer Speed. Access time is the time taken to initiate the actuator by the controller to move the actuator arm with the read/write heads into position over the proper track. Rotational delay is the time the read/write heads must wait before the intended sector/cluster rotates into position. Transfer speed is the data buffer and transfer rate from the hard drive.

Hard drives are connected to the main board using different interfaces. Enhanced Integrated Drive Electronics (EIDE), Small Computer System Interface (SCSI), Serial Attached SCSI (SAS), IEEE 1394 Firewire, and Fibre Channel are the main interfaces used in modern computer systems. Majority of the PCs uses the Enhanced Integrated Drive Electronics (EIDE) which include popular Serial ATA (SATA) and Parallel ATA (PATA) interfaces.

Hard Disc Drives are mechanical drives with moving parts inside them; therefore, over time and prolonged usage wear and tear occurs, making the device unusable.


RAM stands for Random Access Memory, which is the memory used by the computers for storing data during computing processes. They allow the data to be accessed in any random order, and the data is volatile; i.e. the data is destroyed once the power to the device is stopped.

In early computers, relay configurations were used as the RAMs, but in modern computers systems the RAM devices are solid state devices in the form of integrated circuits. There are three main classes of RAM; Static RAM (SRAM), Dynamic RAM (DRAM) and Phase-change RAM (PRAM). In SRAM data is stored using the state of a single flip-flop for every bit; in DRAM a single capacitor is used for every bit.

What is the difference between RAM and Hard Disk Drive?

• Hard disk drive is a type of secondary storage device belonging to ROM (Read Only Memory) category while RAM is completely another type of memory. Even though every RAM is not a solid state device, common usage refers to the integrated circuit models used in computers.

• The RAM is a volatile memory while HDD is nonvolatile memory. Therefore, when power is disconnected to the circuit, data in RAM is destroyed, but the data in HDD does not change.

• RAM stores active program data (data of the programs running at the time including OS and other software), while HDD stores data which needs permanent space.

• The data in the RAM can be accessed much faster than the data in the HDD

• HDDs are electromechanical devices while RAM is a solid state device and has no moving parts.

• In a normal computer configuration, the RAM size is much smaller than the HDD size (RAM 4GB-16GB / HDD 500GB – 1TB).