Blain's blog

Flash Memory

blain2610 — Thu, 05 Apr 2007 07:10:36 +0000

Flash is electrically erasable programmable read-only memory (EEPROM). It is used in memory cards for peripheral devices such as digital cameras, mobile telephones, PDAs and MP3 players. It is also available as USB memory sticks and, when plugged into a computer’s USB port, behaves like an external disk drive. Flash memory is inexpensive, high-capacity storage and is rapidly replacing floppy disks as portable secondary storage.

A Pendrive

DVD-ROM

blain2610 — Thu, 05 Apr 2007 07:00:24 +0000

Digital Versatile Disk Read-Only Memory. These disks are the same size as CD-ROMs and are made using similar materials and manufacturing techniques. They store about seven times as much data as a CD-ROM, because the track spacing and pit dimensions are smaller.

Optical Disks

blain2610 — Thu, 05 Apr 2007 06:55:50 +0000

Random access time is longer than that of a hard disk, but some optical storage is writeable or even rewriteable, CD-ROM, DVD-ROM (Read-Only), CD-R, DVD-R (Writeable), CD-RW, DVD-RW (Re-Writeable).

CD-ROM
CD-R disks
CD-RW disks

Uses Of Magnetic Tape

blain2610 — Thu, 05 Apr 2007 06:51:19 +0000

Tape is cheap and convenient medium for backup, and is also used for archiving past transactions or other data that may be needed again, such for example, weather records collected over a number of years.

Cartridge tape drivers are in common use for backing up the hard disk personal computers, being much more convenient than using dozens of floppy disks. A cartridge type can store several gigabytes of data.

Magnetic tape

blain2610 — Thu, 05 Apr 2007 06:45:56 +0000

Data is recorded in ‘frames’ across the tape, with one frame representing one byte. The frames form tracks along the length of the tape, with 9 traks being common, giving 8 data tracks and one parity track.

Magnetic tape is a serial medium, meaning that to access a specific record, one must start at the beginning until he/she reaches the data required. Likewise, it is impossible to read a record, amend it in memory and the backspace to the beginning of the black and overwrite the old record. Therefore, updating a magnetic tape file always involves copying the file to a new tape with the amendments made.