Computer-Storage Devices

Storage Devices

"How it saves data and programs“

Hard disk drives:

are an internal, higher capacity drive which also stores the operating system which runs when you power on the computer.

The hard disk is housed inside the hard drive, which reads and writes data to the disk. The hard drive also transmits data back and forth between the CPU and the disk. When you save data on your hard disk, the hard drive has to write thousands, if not millions, of ones and zeros to the hard disk. It is an amazing process to think about, but may also be a good incentive to keep a backup of your data.

Floppy disk drives:

allow you to save work on small disks and take the data with you.A floppy disk is a magnetic storage medium for computer systems. The floppy disk is composed of a thin, flexible magnetic disk sealed in a square plastic carrier. In order to read and write data from a floppy disk, a computer system must have a floppy disk drive (FDD). A floppy disk is also referred to simply as a floppy. Since the early days of personal computing, floppy disks were widely used to distribute software, transfer files, and create back-up copies of data. When hard drives were still very expensive, floppy disks were also used to store the operating system of a computer.A number of different types of floppy disks have been developed. The size of the floppy got smaller, and the storage capacity increased. However, in the 1990s, other media, including hard disk drives, ZIP drives, optical drives, and USB flash drives, started to replace floppy disks as the primary storage medium.

Types of Floppy Disks
The first floppy disks that came on the market were 8 inches (200 mm) in diameter. The disk was protected by a flexible plastic jacket. An 8-inch disk back in the late 1970s could store about 1 MB of data. This was quickly followed by a smaller version of the same design, the 5.25-inch (133 mm) floppy, which could store about the same amount of information using higher-density media and recording techniques.
In the early 1980s, the 3.5-inch (90 mm) floppy, or micro floppy, came on the market, and this type became the dominant storage medium for personal computers for many years. Each of these floppy disks required a different type of floppy disk drive. These were typically built into the computer case itself.
Floppy disks were quite vulnerable. The disk medium was very sensitive to dust, moisture, and heat. The flexible plastic carrier was also not very sturdy. The hard plastic case of the 3.5-inch floppy presented a substantial improvement in this respect. The most common format of this floppy became the double-sided, high-density 1.44 MB disk drive.

Hard Disks: 

 Speed:  Very fast! 

 The speed of a hard disk is often quoted as "average access time" speed, measured in milliseconds.  The smaller this number the faster the disk.

 Capacity:  Enormous!  Often 40/80 Gigabytes.  A Gigabyte is equivalent to 1024 Megabytes.

 Cost: Hard disks costs are falling rapidly and normally represent the cheapest way of storing data.

Diskettes (Floppy Disks)

A floppy disk is a storage medium that consists of a thin and flexible magnetic disk inside a plastic carrier. Widely used since the 1970s until the early 2000s, they have gradually been replaced by other storage devices with greater capacity.

 Speed:  Very slow!

 Capacity:  Normally 1.44 Mbytes.

 Cost:  Very cheap.

CD-ROM Disks:

A CD-ROM  is a pre-pressed optical compact disc which contains data. The name is an acronym which stands for "Compact Disc Read-Only Memory". Computers can read CD-ROMs, but cannot write to CD-ROMs which are not writable or erasable.

 Speed: 

 Much slower than hard disks.  The original CD-ROM speciation is given a value of 1x speed, and later, faster CD-ROMs are quoted as a multiple of this value.

 Capacity:  Around 650 Mbytes and more.

DVD Drives:

An optical disc drive that reads and writes all common CD and DVD formats. All modern optical drives that come with personal computers are CD/DVD drives. See DVD writer, CD-ROM drives and DVD drives.

 Speed: Much faster than CD-ROM drives but not as fast as hard disks.

 Capacity:  Up to 17 Gbytes.

Cost: Slightly higher than CD-ROM drives.