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COMPUTER STORAGE DEVICES Computer Memory This is the part of the computer where data, programs and information are stored for use of the computer. It comes in form of a chip. The basic unit for computer memory is byte. Other units are KB, MB, GB, etc. All computers have memory units. The programs a computer is running as well as the data are all stored in memory. Types of Computer Memory Main memory or primary memory Secondary or Auxiliary memory (1) Primary Memory This is the storage area where data and instructions in use by the processor are kept. It is also called the main memory or internal memory. The processor directly stores and retrieves information from the primary memory in a random way. Examples are RAM, ROM (2) Secondary Memory This is the memory that permanently stores data and information for the computer. This memory is slower and cheaper than primary memory but stores more data and information. It is a non-volatile memory and not under direct control of the CPU. The data and information stored in a secondary memory remains there for a long time until the user deletes it or mishandle the memory. Most secondary storage devices can be removed from the system unit without disturbing the working of the computer. They are mostly used to transfer data and programs from one computer to another. Data and information must be loaded to the main memory before the processor can work on them. Special electronic device called drive is used in reading and loading the contents of the secondary memory to the main memory. Examples of secondary memory Optical disk (DVD, CD) Floppy Disk Flash Disk Hard Disk Zip Disk Memory Card Magnetic Drum Magnetic Tape Magnetic Disk, etc. Optical Disks: These are storage media that records data using a low power laser beam. The laser beam alters the surface of a plastic or metallic disk to represent common types of optical disks are compact disk, DVD, etc. Computer Disk: This is a small portable, round medium used for recording and playing back of audio, video, text and other information in digital form. Basic types are CD ROM, CD-R, and CD-RW. Most CD have a capacity of 650MB of data which is capable of playing about 1 hour of video. DVD: This is an app optical disc technology with a 4.7 gigabyte storage capacity, which is enough for a 133 –minute movie. DVDs can be single-sided, and can have two layers on each side. A double-sided two-layered DVD will hold up to 17 gigabytes of video, audio or other information. Types of DVD formats are DVD video, DVD-ROM, DVD-Audio. DVD was originally said to stand for digital Video Disc, and later for digital versatile disc. Floppy Disk: This is made of a round magnetic substance enclosed in a rectangular plastic casing. Earlier floppy disks store data only on one side. These are called single-sided diskettes. However, a later technology of floppy disks store data on both sides. These are called double-sided floppy disks. Floppy disks are in three sizes and capacities. These are 8 inches, 5 ¼ inches and 4 ½ inches sizes. Also the capacity of floppy disks are 360mb (low density) 720mb (double density) as well as 1.44mb (high density). Hard Disk: This is also called fixed or internal disk. Hard disks are the most common disks in computer system where data can be stored and read. Reading and writing of data into the hard disks is faster than doing the same an most other secondary storage devices. The hard disk is made of metallic platters and is normally mounted permanently inside the computer. Both the disk and the drive are held together in a hard disk. Flash Disk: This is a small removable disk usually plugged into USB port to copy data from or to the computer. It has various sizes ranging from 1GB to 1TB. Also See: COMPONENTS OF COMPUTER (OUTPUT DEVICES) COMPONENTS OF COMPUTER (INPUT DEVICES) HISTORY OF COMPUTING How to design a simple business letter head