You may think you have a large hard drive
but you could be eating up valuable space Jan 21 1997

Take a close look at your hard drive. If you're using DOS or Windows 3.1 or even Windows 95, you're probably wasting big chunks of hard drive space. On a new computer with a large hard drive, you're wasting perhaps as much as 40 per cent of the drive's space.

As with many PC inefficiencies, this problem takes us back to compromises made in the early days of DOS, and carried over in the name of compatibility. In this case, the problem is with the file system--the File Allocation Table or FAT. The FAT keeps track of the address of all the bits and pieces of files spread over your hard drive, the problem being that it can only remember a limited number of addresses. In the earliest days of DOS, that limited the size of a drive to 32 megs. If your hard drive was larger than that, you could run DOS's Fdisk program, to split your hard drive into pieces called partitions. DOS treats each partition as if it were a separate physical hard drive.

As drives became bigger, multiple 32-meg partitions became increasingly awkward. In 1988, DOS 4.0 broke through this barrier with a clever solution. It kept the same limited number of addresses, but let each address refer to a bigger cluster of data, allowing partitions to grow as needed--up to a seemingly massive two-gigabytes limit.

With larger partitions, however, this starts to waste a significant amount of space. Files can't share clusters: even if a file is 64 bytes long, like my Config.sys startup file, it uses an entire cluster--16 kb on a partition that's between 512 meg and 1 gig, and 32 kb on a larger partition. Regardless of a file's size, on average, each file on your drive will waste half a cluster.

The DOS Chkdsk utility reports the number of files and the cluster size, and a little math tells me how much space is being wasted. On this computer, it reports that I have about 7,000 files, and 16 kb per cluster (it calls clusters 'allocation units'). That means I'm wasting about 7,000 multiplied by 16, divided by 2 = 56 megs of space. With 349 megs worth of actual programs and data, that's 16 per cent wasted. If I had a larger hard drive, with 32-kb clusters, the amount of waste would double to 32 per cent. Even with hard drive prices lower than ever, that's a lot less than I thought I was paying for.

There are some solutions:

* Switch operating systems. OS/2 Warp and Windows NT each offer more advanced file systems, HPFS and NTFS, respectively. These allow more addresses for files than the old DOS FAT, and effectively eliminate so-called cluster slack. But that's a rather drastic solution. It may be worthwhile, but not just to save a bit of drive space. (Don't gloat, Mac users: this time, you too are subject to the same inefficiencies as PC users.)

* Compress your hard drive. Compressed partitions, using a commercial product like Stacker or DOS and Windows DriveSpace, are actually a single, large file. As a result, they can store all your files much more efficiently. Some people worry whether disk compression is safe, and it does use up some of your RAM and slow down performance. The Windows 95 add-on Microsoft Plus! package includes a DriveSpace 3 feature that can be set for an oxymoronic 0-per-cent compression. By not actually compressing your data, it causes no slowing of your system, but it does eliminate cluster waste.

* If you buy a new machine with a large hard drive and Windows 95, you'll get FAT32, an improved version of FAT supporting partitions larger than two gigs, using smaller cluster sizes for less waste. You can't add this onto an existing system, and such partitions are not compatible with NT or older versions of DOS.

* You can simply create smaller, multiple partitions. While this adds the confusion of multiple drive letters, it reduces waste (if my partition was smaller than 512 meg, the wasted 56 megs would be halved to 28 megs--eight per cent). And it allows users to, for example, make a partition just for data, making for easier backups. It's also a nice feature if you want to run multiple operating systems on a single machine--create a partition for each operating system, and other partitions for shared programs or data.

The old Fdisk program will still allow you to change your drive partitions but in the process, it will destroy all your data! If you want to work with partitions, get a copy of PowerQuest's Partition Magic. It allows for the nondestructive resizing of partitions. The new version 3.0 supports DOS FAT, OS/2, NT, and the new FAT 32 partitions. You may only use it once, but its $69 price tag is a bargain compared to the time lost destroying and recreating your system if you use Fdisk.*

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Alan Zisman is a Vancouver educator, writer, and computer specialist. He can be reached at E-mail Alan