4 ms·

It's like why the first (hard) drive letter is C.

• cyanydeez 14d ago
  A: drive is 3.5; B: drive is 5.25; C: drive is hard disk
  • alightsoul 14d ago
    Yeah it's a relic from when computers booted off floppy and hard disks were rare and expensive
  • compiler-guy 14d ago
    Even further back into time, before 3.5" disks, both A: and B: were 5.25" disks. And, although my memory is hazy, 3.5's were commonly slotted into B: at first, because no one had 3.5" boot disks until the drives became somewhat common.
    • gumby 14d ago
      You are forgetting 8” floppies. IBM used only the soft sector ones (one hole punched close to the spindle to mark sector 0) but there were also hard sector ones (a ring of 32 holes close to the spindle hole). There was a lot of experimentation back in those days. The Wikipedia’s page on floppy disks is surprisingly long!
      • compiler-guy 14d ago
        Trust me, I will never forget 8" floppies. But in the context of drive lettering, although CP/M supported 8" floppies, MS-DOS never did. MS-DOS adopted the naming scheme, but not the boot style.
        • kjs3 13d ago
          MS-DOS 1.25 supported 8" disks. I think 2.0 still did.
      • jasomill 14d ago
        Floppies, superfloppies, removable hard disks (platter-only, as opposed to modern external hard drives that incorporate the entire drive mechanism), magneto-optical disks, rewritable CD/DVD, even today magnetic tape is still used as removable storage in applications where large capacity is required and shelf life is more important than fast random access.
      • LukeShu 14d ago
        But those weren't on "IBM PC"-compatibles, just older micros? The 5150 had 5¼" drives. That is: (Q|MS|PC)-DOS never supported 8" floppies, right?
        • adrian_b 14d ago
          8" floppy drives were not compatible mechanically with IBM PC cases, but there were 8" floppy drives with their own enclosures and power supplies, which could be put on a desktop along the PC case. IBM PCs have never supported 8" floppy drives, but it was easy to make an adapter between IBM PC floppy cables and 8" floppy drives, so there have existed IBM PC clones from countries where 5¼" floppies were scarce (e.g. Eastern Europe), which supported the attachment of 8" floppy drives. The original 5¼" floppies had only the size advantage, but they had both a lower capacity and a lower speed than 8" floppies, so attaching 8" floppy drives would have been a higher performance option in the beginning. Only after the IBM PC/AT introduced the high-density 1.2 Mbyte floppy disks, the 5¼" format matched (actually very slightly exceeded) the performance of the old 8" floppies.
        • kjs3 13d ago
          MS-DOS 1.25 supported 8" disks. I think 2.0 still did.
    • raldi 14d ago
      The floppies got A and B because hard drives were expensive and for a time a lot of people got by without them, though everybody had at least one floppy. Even if you only had one floppy, it was both A and B, so you could say "copy a:DOC.TXT b:" and it would read the doc and then ask you to insert the floppy you're considering B (and depending on file size and available memory, sometimes switch back and forth a few more times)
    • wolrah 14d ago
      I have vague memories of something like this from my childhood, where my family's IBM 486SX had the 3.5" drive on A and the 5.25" drive on B but my grandparents' Epson 286 had the opposite. Also learning about disk densities when none of the disks from the 486 worked on the 286.
  • dspillett 14d ago
    A: and B: were not specific to the type of drive. It was common to have two drives before fixed storage became common, often you would have the application disk in one and your data disk in the other though there were other common use patterns for two drives also (with the OS, or at least the core of it, resident in memory you can copy and otherwise manage data over two data disks, and so on). The first hard-drive in a system was made C: to reserve A: and B: in part because there was software out there that assumed A: and B: were floppy drives and could cause problems if something else was allocated to those signifiers. There are many things that are due to long forgotten compatibility issues like this (try naming file LPT1 under Windows to see another). Another reason is that the BIOS on many PCs was just hard-wired to assume two floppy drives so DOS would see that even if there were no drives really there.
    • brewmarche 14d ago
      I thought MS-DOS had special handling for A: and B: since it allowed you to copy from A: to B: even with just one floppy drive.
      • dspillett 14d ago
        Yes, it did, or something did (maybe the individual commands rather than it being through the OS). I'd completely forgotten about that…
        • jasomill 14d ago
          Both of these things are true: commands like diskcopy have special handling to allow the same drive to be used as both source and destination, and the DOS I/O has special handling to request disk changes from A: to B: on single-drive systems for programs that lack specific support.
      • jasomill 14d ago
        It does. https://github.com/microsoft/MS-DOS/blob/2d04cacc5322951f187bb17e017c12920ac8ebe2/v4.0-ozzie/bin/DISK2/BIOS/IBMBIO.ASM#L1428 https://github.com/microsoft/MS-DOS/blob/2d04cacc5322951f187...
  • kjs3 13d ago
    MS-DOS didn't have built in support for 3.5" drives until version 3.2.