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There's nothing quite as alluring as the thought of getting something for nothing. If you don't believe me, well, then tell me why lotteries are so successful? :^) In the PC world overclocking has become all the rage of late, promising to let folks run their PCs faster at little additional cost. In the storage world, the enticement comes in the form of a technique that lets you store up to twice as much data in the same amount of hard disk space. Sound good? :^) Well, it does to many others as well, and this is why disk compression has been a popular technology for many years.
There are actually many different types of disk compression. It is possible to compress individual files or directories on a hard disk, or even compress an entire disk volume. Today, hard disks are so cheap and so large that compression has become much less of an issue than it once was--few people need to bother compressing a disk volume when you can get a 40 GB hard disk for so little money! However, we are still only a few years removed from the time when PCs had hard disks one hundred times smaller than this. In the 1990s, many PC users needed disk compression just to allow them enough room for the latest operating system, and for their applications and data files. You may still encounter PCs with compressed volumes on them, especially if you maintain a number of PCs in an environment that includes older hardware.
Even though volume-based compression is not used much any more, compression itself remains widely used. Compression not only saves disk space, it can help you organize and archive older files that you don't use regularly. It has also become a standard for allowing the easy downloading of large numbers of files from the Internet. Compression allows them to be packed into a single file that takes less time to transmit than if the files were sent in their regular format.
In this section I talk about disk compression in detail. First, I discuss why disk compression works, describing its fundamental concepts of operation. I then talk about the different types of compressions that are commonly found in the PC world. I then describe volume compression, how it works and what products exist to implement. I then explain file-based compression. Several pages follow that describe how to use compression to reduce slack on FAT16 partitions, how to adjust the compression level in volume compression products, and memory and reliability issues associated with volume based compression.
Note: The NTFS file system
includes compression as part of the operating system. See
here for a description of this NTFS feature.