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Disk Compression

by Oscar Sodani
February 26, 2003

Oscar Sodani is a founder of Help2Go and owner of Help2Go Networks, an IT consulting firm in the Washington D.C. area. Oscar holds the CISSP certification as well as industry certifications from Microsoft, Cisco and Novell.

By using hard drive compression utilities, you can effectively double the size of your hard disk. This is a must topic for anyone who has a very small hard drive and an older machine.

With this guide, our aim is to show you:

  • How compression utilities squeeze your files
  • The goods on doubling your hard disks

The Big Squeeze

Have you ever bought a big appliance, like a TV, VCR, or computer, and you didn't want to throw the box away? You just had a sinking feeling that in a year or five years you would move and you would DESPERATELY need that box. Or maybe you were afraid that you would have to return the appliance in a week or two, so you placed the box in the attic.

Well, boxes take a lot of space (and there isn't anybody who couldn't use more space), so the best way to store them is the fold them up and make them flat as a pancake. Much easier to store. The same thing goes for files on your computer. That's how compression was born.

Compression takes all the zeros and ones that make up your computer files and folds them up, making them take up less space. Compression utilities use complex mathematical formulas called algorithms, passing the contents of your file through the math and ending up with something smaller. None of the contents of your file is lost, it's just been replaced with a computer "shorthand". To get your full file back, the utility passes the compressed file through the algorithm backwards. Whammo! You have you old file back, without the shorthand.

Uncompressed file

Compressed file
1110001(8 0s)1110001001(9 0s)10(11 1s)0(16 0s)(6 1s) 0001010001(6 0s)11

This is a simple example -- the mathematical algorithms can do many more "shorthand" substitutions based on patterns it finds in the data. Compression utilities squeeze your files, on average, to 50% their original size. However, it is important to note that once a file is compressed, it almost always must be uncompressed before you use it again in an application like Microsoft Word. That's why most people only compress older files they want to keep but don't use anymore.

Utilities exist that compress your ENTIRE hard drive. One such utility, DriveSpace, is included with Windows 95/98. It can turn your aging 500 megabyte hard drive to a 1 gigabyte paradise. But read on -- paradises are never what they seem.

Doubling Your Drive

Hard drive compression was introduced a decade ago by a company called Stac. Their product, Stacker, promised to double your hard drive with you hardly noticing it was there. Stacker was a very successful product (it worked miracles on my 30-megabytes hard drive), so Microsoft did what it does best: it stole the idea and incorporated it into DOS. Stac sued, and forced Microsoft to remove it, but the damage had been done. Windows 95 included a handy little utility called DriveSpace in its "Accessories" folder, and Stac lost its flagship business.

Macintosh users have their own program, called DiskDoubler, that promises to do the same. Let me come out and say one thing: these programs work. They work very well, and you DO end up with twice the hard drive space. But oh, the pitfalls...

Drive compression works by taking your entire hard drive and "zipping" it up into one large, compressed file using the algorithms described above. It then fools your operating system, be it DOS, Windows, or MacOS, to treat that file as if IT were your hard drive. Due to some early disasters with data corruption and unreliability, Microsoft and others have improved these disk doublers greatly and they are now extremely stable. knew the BUT had to be coming...But the major problem introduced by disk compression is SPEED, or rather, lack of it. Disk compression slows down your hard drives by a noticible margin, because every time you open a file, it has to be decompressed into memory. And everytime you save a file, more memory is taken up by the compression process. Of course, the makers of the software packages advertise that the difference is imperceptible. They lie. The difference is indeed perceptible, and I urge everyone to avoid the call of "disk doubling" of any sort.

Here's why: hard drives are fairly cheap! Huge hard drives can be had for as little as $100, and the amount of spce you get per dollar spent has doubled every year in recent memory. For instance, in 1996 I spent $200 on a 1 gigabyte hard drive. In 1999, I bought 10 gigabytes for $200. Now, you can get more than 120 gigabytes for the same price! Don't slow down your PC with disk compression, if it is anything like mine, it's probably slow enough. The performance hit just isn't worth it.

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