Data is the driving force of any system that uses computers. Data availability is the reason the Internet became popular, and the ability to modify, store, process, and retrieve data is a major reason why computers are used in homes and businesses around the world. The term storage media usually refers to a means of storing data permanently, and numerous methods can be used to store data more or less permanently on several different media types. These methods include storing data magnetically on a disk or using optical disks.

We’ll look at various types of fixed and removable media, and learn how they store (and sometimes lose) data.We’ll also look at one of the most common data types that is saved to media and analyzed in computer forensic examinations: images. Image files com- prise digital photos, line art, and other graphical representations of people, places, and objects that can be saved to a storage device or other medium. As we’ll see, these files can be created in a variety of different formats, and numerous techniques and tools can be used to view and recover damaged files.

Overview of a Hard Disk

Although removable hard disks exist, most HDDs are designed for installation inside a computer, and for that reason they were referred to as fixed disks.To avoid having to purchase custom or proprietary hard disks to fit inside different brands of computer, standards were developed early in the PC’s history.These standards dictate the size and shape of the hard disk, as well as the interfaces used to attach it to the computer.These standards are called form factors, and they refer to the physical external dimensions of the disk drive.The most common form factors that have been used over the past few decades are:


5.25-inch These were the first hard drives that were used on PCs, and they were commonly installed in machines during the 1980s.
3.5-inch This is the common size of form factor used in modern PCs.
2.5-inch This is the common size of form factor used in laptop/notebook computers.

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Types of Disk Drives

A disk drive is a mechanism that reads data from a disk and writes data onto a disk. The disk in the disk drive rotates at very high speeds, and heads in the disk drive are used to read and write data. Different types of disk drives use different types of disks. For example, a hard disk drive (HDD) accesses hard disks, and a floppy disk drive (FDD) accesses floppy disks. An optical disc drive (ODD) reads and writes the data from optical discs.

Fixed: These are drives like hard disks, which use media that are not removable.

Removable: These are drives that use media that are removable. A few examples of removable storage devices are:

Floppy disk: This type of drive uses media that are portable magnetic disks on which data and programs can be stored. Floppy disks are disks that are made of either flexible or rigid plastic material.The storage capacity of a floppy disk varies, but typically floppies can hold very little.
DVD: DVD is an acronym for digital versatile disc. It is a type of optical disc that holds far more information than a CD-ROM. A DVD can hold a minimum of 4.7 GB of data to a maximum of 17 GB.
Zip disk: Zip disks are used to hold data that requires more storage than a floppy disk can provide. Zip disks are used to back up disks and larger documents. Like floppy disks, Zip disks can be written to multiple times.

Data is organized on a hard disk in a method similar to that of a filing cabinet. The user can easily access the data and programs. When a computer uses a program or data, the program or data is copied from its location to a temporary location. When a user makes changes to a file, the computer saves the file by replacing the older file with the new file. Data is recorded magnetically onto a hard disk. A rapidly spinning platter is used as the recording medium. Heads just above the surface of the platter are used to read data from and write data to the platter. A standard interface connects a hard disk to a computer. Two common interfaces are IDE and SCSI.

Characteristics

Capacity of the hard disk
Interface used
Speed in rotations per minute
Seek time
Access time
Transfer time

Once damaged, a hard disk usually cannot be repaired. When a disk fails, recovering data from it is possible only after installing a new hard disk and accessing the damaged disk as a secondary drive.

Physical Makeup

A hard disk is a sealed unit containing a number of platters in a stack. It can be mounted in a horizontal or vertical position. Electromagnetic read/write heads are positioned above and below each platter. As the platters spin, the drive heads move in toward the center surface and out toward the edge. In this way, the drive heads reach the entire surface of every platter.

On every hard disk, data is stored in thin, concentric bands, called tracks. A drive head reads from or writes to a circular ring called a track. On a 3.5-inch hard disk, there could be a thousand tracks. Tracks consist of sectors, the smallest physical storage units on a hard disk. A sector is almost always 512 bytes (0.5 kilobyte) in size. Figure 1-1 shows the parts of a hard disk.

Zoned Bit Recording

Data is recorded onto a hard disk using a method called zoned bit recording. Zoned bit recording is also known as multiple zone recording (zone recording). In this technique, tracks are combined together into zones depending on their distance from the center of the disk. Each zone is assigned a number of sectors per track. There are three types of data densities on a hard disk:

Track density: Space between tracks on a disk
Area density: Number of bits per square inch on a platter
Bit density: The bits per unit length of track

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http://www.futuristicsec.com/blog/2016/hard-disk/

Very cool