ROM • ROM is short for Read Only Memory. • It is permanent, long-term memory which cannot be erased or changed in any way; • It is also known as “Non-Volatile Memory” because it doesn’t disappear after the computer is switched off.
ROM cont’d • ROM chips instruct the computer how to load the operating system from the hard drive into the computer’s memory. • Don’t confuse the hard drive with ROM – the hard drive is an internal backing store (storage device).
RAM • RAM (Random Access Memory) is:- • Temporary, short-term working memory; • Only works when the computer is turned on; • It is also known as “Volatile Memory” because data disappears if the power is switched off. • Each time you start a program e.g. MS Word, it is loaded into RAM. • The amount of RAM influences processing power, speed and how many programs can run at the same time. • Many computers are now sold with 128 or 256 MB of RAM.
Measurement of Memory • Computer memory is measured in bytes. A single byte is made up of a series of 1's and 0's, which are known individually as binary digits or “bits”. • This is the way the computer communicates and stores information. With each keystroke or character a byte of memory is used. • 8 bits = 1 byte • 1024 bytes = 1 kilobyte • 1024 kilobytes = 1 megabyte • 1024 megabytes = 1 gigabyte
Data Storage - Internal Backing Store • Hard Disks are the main internal backing store usually found inside computers. • The main benefit of hard drives is that they have a large storage capacity – 20 gigabytes or more. (1 Gb = 1024 Mb).
External Backing Store • Floppy disks are a common externalbacking store, however only store up to 1.44 Mb of data. • When are they useful? • Excellent for transferring small files of data from one machine to another and for backing up important small files stored on your hard disk.
External Backing Store • CD-ROM (Compact Disk Read Only Memory) disks are optical disks that use the same technology as musical compact disks. • They store up to 700 Mb of data and a laser beam is used to read the data off the disk. • What can they be used for? • As CD-ROMs are much bigger than floppy disks, they can be used for multimedia applications such as encyclopaedias and can store pictures, sounds and video clips.