Q: I have a PC with the original release of Windows 95 and a 4GB hard drive split into two partitions, C: and D:. My CD-ROM drive is E:. But when I added my new 6GB hard drive, all the drive letter assignments shifted. Now my D: partition has become E: and my CD-ROM drive is H:. And Windows can't locate software programs and files that it expects to find on the original D: drive or on the CD-ROM. Is there any way to add my new hard drive and preserve the old drive letter assignments?

Rex Fairbairn

A: Yes and no. Saving your D: drive designation is no problem thanks to a little DOS trickery. Unfortunately, you won't be able to keep the same CD-ROM drive letter this time, but you can change the current CD-ROM drive letter so it won't change in the future.

Each time you start your PC, Windows assigns a single letter to each of its drives. The letters A: and B: are assigned to floppy drives. (If you have only one floppy drive, B: is not used for other drive types.)

From there, drive assignments become more complicated. A subsequent letter, starting with C:, is assigned to each partition on each drive in your hard drives or Zip or tape drives. Because many hard drives come with just one partition, they have only one letter assignment.

In your particular case, the original version of Windows 95 recognises drives only up to 2GB in size, so your 4GB hard disk is divided into two 2GB partitions. Partitions are created when your hard disk is first set up, using the DOS fdisk utility or another utility such as PowerQuest's PartitionMagic. Using fdisk deletes any existing data. PartitionMagic is easier to use and lets you keep your data intact. When you create partitions on your hard disks, you must choose one of two types: primary or extended. Only hard disks with primary partitions are bootable. On your hard disk, C: is a primary partition. There's usually only one primary partition per drive, but extended partitions can be divided up into multiple "logical" (in other words, virtual) drives, each with its own drive letter. Your D: partition is a logical partition.

When Windows launches and assigns drive letters, you might expect it to assign letters to all the partitions on one hard disk and then, in an orderly fashion, move to the next hard disk and do the same. Not so. Instead, Windows gives the first letter (C:) to the first primary partition on the first drive. The next letter (D:) goes to the primary partition on the second hard drive. And so on. FIGURE 2 shows how drive letters are assigned.

Once the primary partition on each drive has a letter, Windows goes back to the first drive and begins assigning letters to all the logical partitions on the first drive, then to those on the second, and so on. When you added the second drive to your system, Windows assigned the letter D: to the primary partition on your new drive and E: to your old D: partition on your original drive.

Fortunately, the fix is easy. Just use fdisk or a utility such as PartitionMagic to create only an extended partition on your second disk. Since you aren't booting your system from this disk, there's no need for a primary partition.

To avoid future changes in your CD-ROM drive letter, assign this drive a letter in the middle of the alphabet that won't be changed by new drives or partitions. Select the CD-ROM drive in Device Manager, open the Settings tab, and select a letter in the Reserved drive letters box.