The Hard drive is the mechanism that is used to store all of your computer's information. The hard drive enables you to save data on your computer for quick access, oftentimes without using any additional programs. It works by reading bits on a magnetic disk that can be magnetized so they are either 'on' or 'off'. For the hard drive to work, many components go into it.


The Outer Casing


The outer casing of the hard drive is made out of a non-magnetic metal, usually aluminum or steel. This construction is important because if the outer casing was magnetic then the disk would be able to magnetically read all the information from other disks in any computer near it, which is not desired when you want your programs and data kept private. The case also protects the inner workings of the hard drive. Layers of shock absorbent foam and rubber line most drives to soften impacts and keep dust away from sensitive internal parts thus preventing malfunctions due to either physical damage or particles interfering with electronics.


The Read/Write Head


The read/write head is the part of the hard drive that reads and writes all of your data. There are two types of heads used in drives: An Actuator Arm and a Thin-Film (TF) head. The TF head is by far the most common as it is virtually indestructible, whereas an Actuator arm physically moves its way across the disk platter, moving from track to track as needed; At times this can lead to failure. Both heads "fly" on very thin layers of air as they zip around the disk platter at 5400 & 7200 RPM (revolutions per minute). It should be noted that these heads not only need to fly on a layer of air, but they also must maintain a very close distance from the disk platter to be able to read and write data. This is because most hard drives use what's called an inductive head which moves over the disk by producing changes in magnetic flux. The heads are so close to the disk surface that you can see them hovering over the disks when you open up your computer case!

The Actuator Arm


Also known as a "slider," this arm has the responsibility of moving the head out over the disk platters while it spins at high speeds. A small coil on one end of its axle produces a magnetic field that interacts with similar fields produced by fixed magnets attached near each track of each platter.



A hard disk's data is recorded by magnetizing a thin film of ferromagnetic material on both sides of the disk. Binary data bits are represented by sequential changes in the direction of magnetization. The information is read from the disk by monitoring the changes in magnetization orientation. User data is encoded using a method such as run-length limited encoding, which specifies how the magnetic transitions should be used to represent the data.


The read/write head which reads and writes the data is attached to an actuator arm, a metal part that slides across a "rail" mechanism as it moves from point to point on the platters. The rail is made up of two separate, parallel conductors: one for the reading element and one for moving the head itself. These rails sit just below the surface of the disk.


An SSD (Solid State Drive) is a solid-state non-volatile storage device that has been embraced by many firms as an alternative to, and subsequent replacement for, hard disks. SSDs are faster than hard drives since there is no delay (no read/write head to move). They are also more durable and dependable, with better protection in hostile environments. Furthermore, SSDs use less power and are immune to magnets. However, the price per gigabyte is much higher for SSDs than it is for HDDs.


Modern hard drives use a metal alloy platter that stores all of the data although most people associate this with magnetic tape. The disk itself has two sides exposed to a read/write head that floats above its surface and records or retrieves data by changing the orientation of magnetized particles on both sides of a disk at a time. Since an HDD needs to be constructed from many different parts whereas an SDD only requires one circuit board, manufacturing costs play a large role in dictating why HDDs are still widely used despite their slow speed and high power usage.

What’s The Difference Between SSD & HDD?


Another key difference between SSDs and HDDs is how data is stored on each one. Hard disks, which are the more traditional type of storage medium, store data that is magnetically coded onto thin metal plates called platters. These platters are housed in a sealed compartment inside the drive itself (i.e., there's no way to remove them). The platters spin at speeds up to 7200 RPM, while a read/write head moves across its surface to store and retrieve information by changes in magnetization orientation. SSDs on the other hand have no moving parts whatsoever because they use integrated circuits to build memory units known as "blocks," which can then be written or deleted with commands from your computer's processing unit.

The Capacity of HDD & SSD


Hard drives are by far the most common option on the market when it comes to storage, so they tend to be higher-capacity than their solid-state counterparts. Because SSDs do not have physical disks with magnetic coding, you can't compare them in terms of capacity between each other. But while hard drives typically range up to 4TB of storage these days (with 8TB models on the way), a high-end SSD may only provide 256GB or 512GB of space.


While modern SSD's are still much more expensive per GB than HDDs, prices have been steadily dropping over time and this is predicted to continue - especially if HDD sales continue declining. One example would be for a family that needs a large amount of storage space and cannot afford to spend a fortune on hard drives: an SSD could be used for the operating system and critical applications, while several hard disk drives could then be kept for long-term storage.