[RndTbl] Dimensional hard drives?

Adam Thompson athompso at athompso.net
Mon Jan 21 15:18:35 CST 2013

Ever double-check an assumption, only to find it false, and feel like the rug just got yanked out from under your feet?

Go measure the width of a so-called 3.5" hard drive.  Yeah, go ahead.  It's 4" wide.  Now go measure the width of a so-called 2.5" hard drive.  Uh-huh... it's 2.75" wide.  I just (re-?)discovered that and felt just as cheated as when I found out that the nominal sizes of dimensional lumber are complete B.S.!

I knew this once upon a time, but I guess I forgot... 5.25" & 3.5" refer to the fact that it fits into the bay where you would have been able to fit a floppy drive accommodating the corresponding-size floppy disk.  I can't find any derivation for why we call a 2.75" drive a 2.5" drive, since there's no such thing as a 2.5" floppy[1]!  Perhaps the internal platter is 2.5" wide?

(See: http://en.wikipedia.org/wiki/Hard_disk_drive#Form_factors)


[1] OK, yes, there a 2.5" floppy did exist briefly, but it was never any sort of standard and I've never seen one in person AFAIK.  FYI, the Sony micro-floppy format was not 2.5", it was 90mm (closer to 2", anyway).

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