Basically, a partition is just a section of a hard disk; a single partition covering the whole drive is usually known as the familiar C:. You can divide a drive into multiple partitions of any size, each with its own drive letter.

Repartitioning can provide better organisation and easier backups. Storing data on its own partition away from applications means you can easily drag and drop a drive icon onto your backup device's icon. If you're using a 100MB Zip drive for backups, for example, storing your files in convenient 100MB partitions can save you from tedious sorting.

But what's really cool is that repartitioning lets you squeeze more space out of your hard disk ù maybe lots of space.

You get this added space because of the way data is stored on the disk, in fixed-size chunks called clusters. On DOS, Windows 3.x, and many Windows 95 systems, clusters range in size from 2KB to 32KB depending on the size of the partition. The smaller the cluster, the more efficient your disk, since each file on the disk must use at least one cluster, and any unused space in the cluster is lost.

If you cram your disk with zillions of small files, this wastage adds up. Say you've got 500 e-mail messages, each stored in its own small text file on a 1.2GB, single-partition FAT16 disk. That probably translates to around 8MB of wasted space. By comparison, if the files were stored in a 100MB partition ù which uses 2KB clusters ù the lost space would probably be around 500KB.

To check a disk's cluster size, run ScanDisk. Select StartûProgramsûAccessoriesûSystem ToolsûScanDisk, select the drive, and click Start. The third line from the bottom of the Results box shows the number of bytes in a cluster (also known as an allocation unit).

If you're running DOS, Windows 3.x, the original Windows 95, or Windows 95 upgraded with Microsoft's Service Pack 1 (Version 4.00.950A), you must divide your disk into smaller partitions to get smaller clusters.

But if you're lucky enough to be running the new, upgraded version of Windows 95, version 4.00.950B, you have another choice. (Check your version by right-clicking My Computer, selecting Properties, and then looking under the General tab.)

Version 4.00.950B, also called OSR2, supports FAT32, an improvement on the original FAT16 file system that DOS and older versions of Windows 95 use to keep track of the location of files on your hard disk. FAT32 offers several improvements, including a maximum partition size of two terabytes ù up from FAT16's 2GB limit ù and much smaller clusters on large partitions ù only 4KB on partitions up to 8GB.

Note that FAT32 is available only on new PCs sold in the last year and a half (and on the soon-to-be-released Windows 98). And not all of these PCs come with FAT32 enabled.

Caption: Disks with the FAT16 file structure fritter away space ù unless you kep your partitions small. The upgraded FAT32 file structure means big savings for big drives

Whether you're trying to reduce your disk's cluster size with FAT32 or with smaller partitions, here's what to do.

DOS and Windows 95 come with two key utilities: Fdisk, which deletes and creates partitions, and Format, which sets up the file system. Both run in DOS mode and can be found on Win 95's start-up disk.

Caption: Check your current partition status with Fdisk. Here, multiple partitions have been established

But using Fdisk and Format on a hard disk with data already on it is no walk in the park. Fdisk makes you delete existing partitions before you can create new ones. And that means losing all your data. So you'll have to back up everything you want to keep to a separate disk or tape, and then copy it back to a newly repartitioned disk.

Use Fdisk to decide on your repartitioning strategy before deleting partitions. First, insert your start-up disk in drive A: and reboot. From the command line, run Fdisk. To learn about partitions and see how your drive is partitioned now and what each partition's drive letter assignment is, select choice 4 on Fdisk's menu.

Caption: Divide your hard disk into a primary partition (which must hold the operating system) and an extended partition (which can hold one or more logical drives)

There are three types of partitions, which must be created in the following order:

Primary partition. A primary partition must hold a bootable operating system. If you want your computer to be able to boot from more than one operating system, you must create a separate primary partition for each one. DOS and Windows 95 allow up to four primary partitions on a single disk. But Fdisk can set only one as the "active" or bootable partition.

Extended partition. Once you've created a primary partition, you can create additional partitions in the remaining space on the disk. First you must define the unused space as an extended partition. Then you divide that extended partition into logical drives.

Logical drives. Each logical drive has its own drive letter. Typically, a logical drive stores applications and/or data.

When you're ready, you can select Fdisk's choice 3 to delete existing partitions (delete all the logical drives on the extended partition first, then the extended partition itself, then the primary partition). Then reboot, and use Fdisk's choice 1 to create new partitions. DOS and Win 95 will assign new drive letters and possibly reassign some old ones. If an application won't run after repartitioning, check its .ini file to see if you need to change a file address to the new drive letter. Expect your CD-ROM drive's letter to change when adding a partition.

Once your partitions are in place, use Format to set up a file system on each partition. Format will apply FAT16 or FAT32, depending on which version of Windows 95 you're using; you can take your pick if you're running version OSR2.

If you've got lots of software and data, and no handy way to store it while you use Fdisk and Format, you can simplify life by spending a few bucks.

Two great utility programs can repartition your hard disk without moving or losing any data. PowerQuest's PartitionMagic (www.powerquest.com) and Quarterdeck's Extra-Strength Partition-It (www.quarterdeck.com) can save you hours of toil and frustration, and can also convert partitions from FAT16 to FAT32.

Caption: Simplify partitioning with Extra-Strength Partition-It (shown here) or PartitionMagic

When Windows 98 finally arrives, it will bring a FAT16-to-FAT32 conversion utility that Microsoft claims is easy, safe, and foolproof. We'll take a look and see.