HARD DISK

What Is a Hard Disk?

A hard disk or drive is the part of your computer responsible for long-term storage of
Information. Unlike volatile memory (often referred to as RAM) which loses it’s stored
Information once its power supply is shut off, a hard disk stores information permanently,
Allowing you to save programs, files, and other data. Hard disks also have much greater
Storage capacities than RAM; in fact, current hard disks may contain over 1TB of
Storage space.

Basic components of a Hard Disk

A hard disk is comprised of four basic parts: platters, a spindle, read/write heads, and
Integrated electronics.

• Platters are rigid disks made of metal or plastic. Both sides of each platter are
Covered with a thin layer of iron oxide or other magnetizable material.

• The platters are mounted on a central axle or spindle, which rotates all the platters at
The same speed.

• Read/write heads are mounted on arms that extend over both top and bottom
Surfaces of each disk. There is at least one read/write head for each side of each
Platter. The arms jointly move back and forth between the platters’ centers and
Outside edges; this movement, along with the platters’ rotation, allows the read/write
Heads to access all areas of the platters.

• The integrated electronics translate commands from the computer and move the
Read/write heads to specific areas of the platters, thus reading and/or writing the
Needed data.

How Is Data Stored and Retrieved?

Computers record data on hard disks as a series of binary bits. Each bit is stored as a
Magnetic charge (positive or negative) on the oxide coating of a disk platter. When a computer saves data; it sends the data to the hard disk as a series of bits. As the
Disk receives the bits, it uses the read/write heads to magnetically record or “write” the
Bits on the platters. Data bits are not necessarily stored in succession.

The read/write heads can access any area of the platters at any time, allowing data to be
Accessed randomly (rather than sequentially, as with a magnetic tape). Because hard disks
Are capable of random access, they can typically access any data within a few millionths
Of a second.

What Is Disk Formatting?

Computers must be able to access needed information on command; however, even the
Smallest hard disk can store millions and millions of bits. How does the computer know?
Where to look for the information it needs? To solve this problem, hard disks are
Organized into discrete, identifiable divisions, thus allowing the computer to easily find
Any particular sequence of bits.

The most basic form of disk organization is called formatting. Formatting prepares the
Hard disk so that files can be written to the platters and then quickly retrieved when
Needed. Hard disks must be formatted in two ways: physically and logically.

1.Physical Formatting :

A hard disk must be physically formatted before it can be logically formatted. A hard
Disk’s physical formatting (also called low-level formatting) is usually performed by the
Manufacturer. Physical formatting divides the hard disk’s platters into their basic physical elements: Tracks, sectors, and cylinders. See Figure 2. These elements define the way in which data Is physically recorded on and read from the disk.

2.Logical Formatting:

After a hard disk has been physically formatted, it must also be logically formatted.
Logical formatting places a file system on the disk, allowing an operating system (such as
DOS, OS/2, Windows, or Linux) to use the available disk space to store and retrieve files.
Different operating systems (OS) use different file systems, so the type of logical
formatting you apply depends on the OS you plan to install.

File Systems:

All file systems consist of structures necessary for storing and managing data. Some of the most common File systems are the following:
• File Allocation Table (FAT)
• File Allocation Table 32 (FAT32)
• New Technology File System (NTFS)
• High Performance File System (HPFS)
• NetWare File System
• Linux Ext2 and Linux Swap