How Computer Hard Disks Save data

We use hard disk drives (HDD) to store digital data. Not only in computers, CCTV DVRs, modern photocopy machines and etc. use hard disks to store data. 

In this article I will show you how Magnetic disk hard drives work, their Geometry, and how data store in that kind of a hard disk.

If You open the front cover of a Magnetic disk hard drive, you can see something like figure 01. The organization of components may differ from one hard disk model to another, but the components and their functionality is same for all.

Figure 01

Usually Computers save data in binary form (1 and 0). This type of single binary digit equals to 1 Bit. We know 8 Bits equals to 1 byte and 1024 bytes equals to 1 kilo byte and vice versa. Data is stored in the platters. Those data can be read from the read/ write head and pass them to the logic board. When data is received, that data will be placed in platters by the read/ write head. this is the functionality of a hard disk in very simple way. Now lets dig deep.

Platter is a CD shaped round object which is made with most of the time aluminium. A magnetic media is coated on this kind of disks. A hard disk may contain one or more platters. It depends on the capacity and the model of the hard drive.The platter or platters in a hard drive are attached to a motor and they spin in high RPM(Rounds per minutes). The RPM value of a hard disk also may differ from one hard disk to another.

The data actually record in a platter as magnetic patterns. The coated magnetic media on a disk act as microscopic magnetic metal grid something like in Figure 02.

Figure 02

These tiny grids arrange in to groups to store the magnetic pattern of the data. Figure 03.

Figure 03

This type of group is known as a Bit.

Figure 04

Each group has its own magnetization out of one from two possible states.Figure 05 shows how groups get magnetize and how the whole group indicate the state of its magnetization.

Figure 05

This is the mechanism the Magnetic disk hard drive stores 0s and 1s. The magnetization state of a group represent either 0 or 1. See figure 06.

Figure 06

The functionality of the read/ write header is simple. It read and write data from and to the platters. Header is capable of magnetize groups (which stores one Bit) with one of the possible state out of the two states. 

So for the simplicity think like this. With an elector magnet we can change the magnet field direction by changing the DC current direction to the elector magnet. The header in the HDD uses this feature. Basically 1 and 0 in computer hardware id either on or off. When binary signals received to the interface board it convert them to a format which header can handle. Then current passes through the header in one direction to magnetize a group with one of the possible state out of the two states, and when current passes in other direction through header it magnetize a group with other state. figure 07 and 08.

Figure 07

Figure 08

This is the mechanism of a Hard disk of saving data. In another article we will discuss how Solid State Drives Save data. We will discuss about the sectors later in another article.