A Short History of PC Drive Letters

Old Ben from “Star Wars” showed up in my Twitter feed last weekend: “A: Now that’s a drive letter I have not seen in a long time.” I haven’t thought about the A and B drive letters in years. Here’s a short history of drive letters on the PC.

A: & B: (Floppy Drives)

When the IBM PC came out in 1981, it had up to two 5.25″ full-height floppy drives. PC-DOS (MS-DOS for PC clones), the operating system, refers to the floppy drives by drive letters. The first floppy drive was Drive A, and the second floppy drive was Drive B. The PC would boot off the DOS disk in Drive A.

If you have one floppy drive and wanted to run a program, you take out the DOS disk and insert in the program disk. From the A: prompt, type in the name of the executable file to start the program. If you wanted to save data to a different disk, you must remove the program disk and insert the data disk.

If you have two floppy drives, you leave the DOS disk in Drive A and insert the program disk in Drive B. From the A: prompt, type the letter ‘B’ and colon, press the return key to switch from the A Drive to the B Drive, and type in the name of the executable file. Or you can insert the program disk into Drive A and insert a data disk into Drive B.

If the program needed a file from the DOS disk, you swap out the program disk for the DOS disk. Whether you have one or two floppy drives, disk swapping was a fact of life.

C: (Hard Drive)

When the IBM PC AT came out in 1984, it had up to two 5.25″ half-height floppy drives and a 20MB 5.25″ full-height hard drive. Whether you had one or two floppy drives, the hard drive was always Drive C.

A common configuration for many PCs was to have the A Drive and the C Drive. The A Drive was for installing software, saving data, and backing up the hard drive. The B Drive disappeared because no one needed a second floppy drive. The C Drive became the default drive for DOS and later Windows.

Doom Cover Art
Doom (1993)

A college roommate brought home an old IBM PC AT inside an industrial case that bolted to the floor in 1994. He gave me the PC to keep me off his new PC with a 386 processor that could run Doom in full VGA color. The IBM AT had a 286 processor and a CGA video card that couldn’t run Doom. I surprised my roommates by running a WildCat BBS with a 2400 baud modem for two years. And then something called the Internet came along.

D: (CD Drive)

CD drives weren’t widespread until the late 1990s. A common configuration for many PCs was a floppy drive, a hard drive, and a CD drive. The CD drive would often be the D Drive. If a PC had more than one hard drive, the CD drive would take the next available drive.

A common practice was to assign a higher drive letter to the CD drive in Windows. If you add new hard drives, the CD drive letter never changes. Software installed from CDs may hard code the CD drive letter in settings. If the CD drive letter changes, the software could stop working. The fix was to change the drive letter in the settings text file or reinstall the program.

Baldur’s Gate (1998)

“Baldur’s Gate” by Bioware came out in 1998 when I worked as a video tester at Infogrames. A five-disc game that took forever to switch CDs during gameplay. Six of my coworkers each bought a CD changer drive that could hold five discs and made disc switching very fast. They replaced the CD drives in their work PCs on a Friday night. They spent the entire weekend playing “Baldur’s Gate” from start to finish. On Monday morning, they called in sick. Management confiscated the CD changers and the game discs that were still inside the work PCs.

Forgetting About The A & B Drive Letters

The Microsoft Xbox came out in 2001 when I worked as a lead tester at Atari. I read the hardware documentation for the Xbox. The A and B Drives were “legacy devices” that weren’t available for use. Floppy drives weren’t needed on a video game console.

I went back to community college on a part-time basis to learn computer programming from 2002 to 2007. During the early years, I turned in my class assignments on 3.5″ floppy disks. Since my Dell laptop didn’t have a 3.5″ floppy drive, I had a USB floppy drive to save data. During the later years, I turned in class assignments on CDs or USB flash drives.

When I built a new PC for Windows Vista in 2007, I didn’t bother installing a floppy drive inside the case. Motherboards since then no longer had a connector for a floppy drive. I tossed out my old floppy drives when I cleaned out my junk box in 2014. I still have my USB floppy drive if I ever needed it again.

You can remap drives to the A and B drive letters in Windows 10. My test PC has two USB flash drives mapped as the A Drive and B Drive. I can switch back and forth between the two on the command line. Reusing these old drive letters might be useful for someone.

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