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Storage Devices , Harddisk, or Secondary Storage is required to store data and programs within a certain (non-volatile) or also called permanent storage. Compared with the main memory, external storage capacity is greater but in slower access.
External storage can be classified into Direct Access Storage Device (DASD) or direct deposit income and storage Sequential Access Device (SASD).
Examples of external storage
DASD Disk Micro SASD
• Punched Card • Mini Disk Magnetic Disk
• Magnetic Tape • Hard Disk Optical Disk

Example SASD
• Punched Card
Developed in 1887 by Prof.. Dr. Herman Hollerith and for the first time in the United States to process the census in 1890. This card has a length of 18.4 cm, 8.125 cm wide, and 0.0175 cm thick. Each card consists of 80 columns and each column can record 1 characters.
• Magnetic Tape (Magnetic tape)
Magnetic tape is widely used as an external storage since 1950 on the UNIVAC computer. Magnetic tape is made of a thin plastic ribbon coated with iron oxide red-brown color.

Sample DASD
• Magnetic Disk (Magnetic disc)
Foreign savings are made from one or more disc shaped like a phonograph record, made of metal or plastic and its surface is coated with iron oxide. Magnetic disks are made of plastic called a floppy disk, and is made of metal and consists of many disks is called a Hard Disk. Which includes magnetic disk is as follows;
1) Micro Disk, plastic dish made from size 3 ½ inch diameter. One of the micro computers that use these deposits is an Apple Macintosh.
2) Mini Disk,  Introduced in 1972 by IBM as a storage medium for the mainframe computer. Mini Disk or Diskette have Read / Write Protect Notch (read and write protection hole) when closing the disc becomes Read Only nature, ie the information can only be read only. Disks coated with a protective coat called, which serves to protect the disc plastic (floppy disk) that is in it. Organized a mini disk with a circle divided into several so-called concentric track and cross-section is divided into what is called a sector. Amount of information that can be recorded depends on the mini disk density (density) disks. Mini disk density is determined in 2 ways:
• Track density, ie the number of tracks on the surface, as measured by units tpi (tracks per inch)
• Linear Density, ie the number of bits that can recorded per inch for each inch of each track.
3) Hard Disk, Made from hard disks of aluminum or ceramic material coated with a substance magnetic. Because the disk of the hard disk and rigid form, then one can be arranged harddisk up to 100 discs, disc diameter of generally 14 Inch, 8 Inch, for large and mini computers, or 51 / 4 inch for micro computers. Very large hard disk capacity for this already exists today that can accommodate 8 Gygabyte more.

• Optical Disks, In about the year 1980 experiment conducted by North America which then produces Philips Optical Disk System is based on the video disk 12 Inch. Optical Disk has 40,000 tracks and sector 132 can record data for 1 billion characters, and now developed to be store 12.5 billion bytes. Optical Disks have been studied since 1960 by Stanford Ovshinsky who is the inventor of the optical disk.
The process of recording data on optical disks by burning the small dots on the disk surface layer with a laser beam. Because recorded process by burning the optical disk can not be deleted and can not be re-used for other purposes. In 1983, the Japanese company Matsushita has developed an optical disk that can be erased and reused.

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This entry was posted on Friday, December 25th, 2009 at 10:07 and is filed under Computer. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.