Why are external HDD enclosures advertised as 3.5"

Brandon Stout bms at mscis.org
Tue Feb 6 15:35:52 MST 2007

Joseph Hall wrote:

> Oh, great. Next thing you know, there's going to be another class
> action lawsuit just like there was with the monitors. All the geeks
> already knew that a 17-inch monitor didn't refer to the viewable area,
> but somebody had to go and raise a stink. Next think you know, hard
> drives will be sold as "3.5-inch actual platter size" or something.
> * Joseph despairs
> On 2/6/07, Andrew Jorgensen <andrew.jorgensen at gmail.com> wrote:
>> On 2/6/07, Kenneth Burgener <kenneth at mail1.ttak.org> wrote:
>> > I was looking for a simple external HDD enclosure and I couldn't
>> > remember, off the top of my head, if my standard desktop hard drive
>> was
>> > the 2.5" or 3.5" size.  So I pulled out the ruler, and measured the
>> > drive.  It is roughly 5.5" x 4" x 1".  It would seem to me that the
>> 3.5"
>> > size is what I am looking for, but the drive is not 3.5" wide.  Why?
>> 3.5" is the size of the floppy disk that goes in a "3.5"" (use of
>> quotes intentional) floppy drive, which is roughly the same width as
>> your HDD.  Likewise 5.25" refers to the floppy disks that went in
>> drives with that nominal size.

Probably the same reason a 2x4 is actually 1 7/16" x 3 7/16", why 3/4"
plywood is actually 11/16" plywood, and 1/2" plywood is actually 7/16". 
Grab your torches and pitchforks!

Actually, Kenneth has a good point.  You can't enclose a 4" something
inside something meant to tightly enclose 3.5".

Brandon Stout

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