Types of Secondary Storage Media
There are several types of secondary storage media used today in the world, each of these can be compared to each other in terms of portability, speed and capacity. Here are discussions on some Secondary Storage Devices:
Magnetic Tape is a recording medium consisting of a thin tape with a coating of a fine magnetic material, used for recording analogue or digital data. A device that stores computer data on magnetic tape is a tape drive. The capacity of tape media are generally on the same order as hard disk drives (The largest being about 5 Terabytes in 2011). Magnetic Tapes Generally transfer data a bit slower than hard drives, however magnetic tapes are cheaper and are more durable
Floppy Disks were an were a ubiquitous form of data storage between 1980's and early 2000's, However they have now been superseded by data storage methods with much greater capacity, such as USB flash drives. Floppy disks comes in 3 sizes: 8-inches, 5.5-inches and 3.5-inches. The capacities of Floppy disks vary between 1-250 Megabytes and these devices were very slow, reading data at rates of bytes and kbytes/second. However, most are very small and portable.
The hard disk drive is the main, and usually largest data storage device in a computer. It is a non-volatile, random access digital magnetic data storage device. A hard drive is made up of platters which stored the data, and read/write heads to transfer data. A Hard Drive is generally the fastest of the secondary storage devices, and has the largest data storage capacicity, approximately the same as Magnetic Tapes. Hard drives however, are not very portable and are primarily used internally in a computer system. Some persons use hard drives externally as a form of storage and as a substitute for portable storage, hard drives used for these purposes are called external hard drives.
A Hard Disk is divided into tracks and sectors, Data on this hard disk is positioned into these tracks and sectors so they can be easily read by the heads and also to help reduce fragmentation on the hard disk. Below are 2 diagrams depicting how a hard disk is divided into tracks and sectors:
Data on a hard drive are accessed by two methods:
1. Fixed Head: Hard Disks with fixed heads have a read/write head for each track on the hard disk, since there is no moving of heads to access data, the data access time is generally faster for Fixed head Hard Drives.
2. Moving Head: A moving head hard disk is one in which one or more read-write heads are attached to a movable arm which allows each head to cover many tracks of information
Optical disk is an electronic data storage medium from which data is read and written to by using a low-powered laser beam. It is flat, circular, plastic or glass disk on which data is stored in the form of light and dark pits. There are three basic types of optical disks: Read-only optical disks, Write once read many Optical disks and Rewritable Optical disks. Two main types of optical disks are:
CD - is an abbreviation of compact disk, and is a form of data storage that can transfer data up to the speed of 7800 KB/s. A standard 120 mm CD holds up to 700 MB of data, or about 70 minutes of audio. There are two types of CD: CD-ROM and CD-RW, CD-ROM are stands for CD-Read Only Memory and they function the same way Read Only Memory Does. CD-RW Stards for CD-Rewritable, these disks can be erased and rewritten at any time.
DVD: is an abbreviation of Digital Versatile Disc, and is an optical disc storage media format that can be used for data storage. The DVD supports disks with capacities of 4.7 GB to 17 GB and access rates of 600 KBps to 1.3 MBps. A standard DVD disc store up to 4.7 GB of data. There are two types of DVD's: DVD-ROM and DVD-RW. DVD-ROM are stands for DVD-Read Only Memory and they function the same way Read Only Memory Does. DVD-RW Stards for DVD-Rewritable, these disks can be erased and rewritten at any time.
A flash drive is a small external storage device, typically the size of a human thumb that consists of flash memory. USB flash drives are removable and rewritable reads and writes to flash memory. They are a solid-state storage medium that's both inexpensive and durable. Currently, USB 2.0 flash drives on the market are able to reach a data transfer speed of 480 Mbit/s and USB 3.0 has transmission speeds of up to 5 Gbit/s. USB Flash drives vary in sizes from 8 Megabytes to 512 Gigabytes. More commonly used sizes vary from 2 Gigabytes -16 Gigabytes.
Flash Memory cards
Flash memory is a EEPROM non-volatile computer storage chip. These Memory cards currently vary in sizes between 1 Gigabytes -16 Gigabytes and they transfer data at a rate of approximately 14.65 MB/s. Flash memory cards have most of the same characteristics of a flash drive in that they are inexpensive and durable, and are very small. However Flash memory cards are Flat and have a size of about 1 inch * 0.75 inch with a thickness of about 2mm. Flash memory cards also have a smaller version which is used within cell phones; These smaller cards are about 6mmX3mm in size and are less than 1mm thick.