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)
-Adam
[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).
--- Adam Thompson wrote:
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?
Yup. At least they were, manufacturers started shrinking them.
As for lumber: a 2x4 used to be 2" by 4". But that was a rough sawn surface. Today rough cut lumber is 2"x4". Finished lumber used to have 1/8" planed off each face to make it smooth. That made it 1.75"x3.75". Then someone got cheap and decided to sell 1.5"x3.5" lumber, and call it 2x4.
Same with wire gauge. Originally 16 gauge wire was 1/16" diameter. That is 0.0625", but now what is sold as 16 gauge is 0.0508", so 1/19.7". The standard states 16 gauge is "19.7 turns of wire per inch (no insulation)".
Everything is a rip-off, but what are you going to do when it's built into the standards? As long as they're consistent...
Rob Dyck
That's hilarious! It also reminds me of an old tagline:
2 + 2 = 5 for extremely large values of 2.
So, what is the outer width of a 5.25 inch device? (I know, I could just go measure a CD/DVD drive, but I'm not near a raw drive right now.)
Yes, your comments are correct as to how these misquoted dimensions came about. As for lumber, which is badly misquoted in the other direction (especially the ubiquitous 2x4), I once heard an explanation for that, but have forgotten it. Anyone know? (Definitely on topic. I may want to build a computer rack out of lumber. [grin])
Hartmut Sager
On 21 January 2013 15:18, Adam Thompson athompso@athompso.net wrote:
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)
-Adam
[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).
Roundtable mailing list Roundtable@muug.mb.ca http://www.muug.mb.ca/mailman/listinfo/roundtable
I don't get it -- you feel cheated because you paid for something that you thought was 3.5" wide and you got *more*? And it fit perfectly where you wanted to put it? And it had all the other specifications you desired? You're just weird, man.
I always assumed the measurement referred to the physical media, not the device as a whole. Have you measured a 3.5" floppy, with and without the hard shell?
Kevin
On Mon, Jan 21, 2013 at 3:18 PM, Adam Thompson athompso@athompso.netwrote:
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)
-Adam
[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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