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A technique, using special software, to increase the storage capacity of computer media, either by artificially increasing the apparent size of a computer disk, or reducing the size a files stored thereon. Compression comes in two flavours; Disk Compression and File Compression.

Disk Compression dates from the mid-1980's when hard drives were very much smaller and, relatively, much more expensive than today. A typical 1990 hard drive would store 80 Megabytes of programs and data, compared to the year 2000 'basic' home user specification of 4.3 Gigabytes (4,300 Megabytes) - an impressive growth of 5,275%. As a result of vastly increased disk storage capacities, users' enthusiasm for such techniques has, not surprisingly, waned somewhat. Overall, it is generally regarded as being cheaper and easier to install another hard drive than deal with the drive/file structures and performance degradation often associated with disk compression. Companies with computer archives dating back to 1995, and earlier, should review these archives to ensure that the files thereon can still be accessed by the systems and software now being used and, if necessary, give consideration to decompressing such disks and storing the information on new, larger capacity, disks.

File compression, conversely, is being used more frequently. Commonly referred to as 'Zipping' after the most popular compression programs (PKZip, and WinZip) this increase in usage is due in no small part to the increasing use of electronic transmission systems to move files between remote parts of the organisation, and even around the world at large. A typical Word Processor document can be compressed by 90% or more and thus a file of 1 Megabyte can be reduced to 100 Kilobytes. Sending a zipped file not only reduces the cost of transmission, by taking less time to transmit, but also, by the same token, reduces the risk of transmission error. Companies should be aware, however, that unattractive elements such as viruses can be contained within compressed files, ready to activate themselves as soon as the file is decompressed. Consequently, any Anti-Virus software selected by the organisation should be capable of detecting viruses within a compressed file before it is decompressed and brought into the system.

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