February 13, 2011

 CD-ROM

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CD-ROM stands for Compact Disk Read Only Memory is a type of secondary storage or optical disc that users can read only but not write or erase. Philips and Sony companies invented Compact Disc in year 1982. CD-Rom is a WORM (Write Once Read Many times) device.  Typically they can store up to 600-700 MB of data or 70 minutes of audio, also store video, data, and text. The diameter of a Compact Disk is 4.7 inches and its thickness is 0.047 inches. A single Compact Disk equal to : 1500 - 5.25-inch floppy disks, 450 - 3.5 inch floppy disks and 274,000 pages of text.


Types of Compact Disks :

(1)  CD-ROM     :  
Compact Disk Read Only Memory (Write Once Read Many times)

(2)  CD-R       :  
(Compact Disc-Recordable) WORM disks for Well known technology

(3)  CD-RW      :  
(Compact Disc-ReWritable) Rewritable and erasable.

(4)  CD Extra    :  
For Multimedia purpose. Developed by Sony, Philips and Microsoft.

(5)  CD-DA      :  
(Compact Disk Digital Audio) Audio CD, Digital Audio Developed by Philips and Sony companies.

(6)  Photo CD      :  
Developed by Kodak and Philips companies.

(7)  Video CD      :  
Can hold approximately 70 minutes of recorded video.

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January 17, 2011

 Read Only Memory (ROM)

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Stands for Read Only Memory. It is built into the computer. ROM is non-volatile and only permits the user to read data. ROM performs the read operation only does not have a write capability which means we cannot store any new information into ROM. An example of a BIOS (Basic Input Output Systems) chip are permanently loaded during the manufacturing time. ROM holds instructions for starting up the computer. The data does not get erased when the power is switched off.

ROM is 4 Types :

(a) ROM (Read Only Memory) :
This is stored at the time of manufacture of the chips

(b) Programmable Read Only Memory (PROM):
PROM is non-volatile. Once the chip has been programme, the recorded information can't be changed. i.e. the PROM becomes ROM and the storaged information can only be read.

(c) Erasable  Programmable Read Only Memory (EPROM):
It is similar to PROM except that erasing is possible by exposing to ultraviolet light.

(d) Electrically Erasable  Programmable Read Only Memory (EEPROM):
A recently developed type of memory that can be programmed and erased inside a computer system using an electrically signals. EEPROM used in many electronic devices.
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