[USMA:29450] Re: USMA digest 1568 - floppies really are 3.5 in. on one side

Mon, 05 Apr 2004 18:06:36 -0700

IBM was one of the first users of the small diskette, and I guess they felt they had to dumb down the size for the American audience, or to match their 5.25 in diskette (the only real "floppy" diskette; the 90 mm diskette is rigid plastic, and does not flop).
 
Carleton
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]On Behalf Of BigChimp
Sent: Monday, April 05, 2004 18:22
To: U.S. Metric Association
Subject: [USMA:29447] Re: USMA digest 1568 - floppies really are 3.5 in. on one side

There is no such thing as a 3.5 inch floppy disc.

The term 3.5 inch floppy disc is in fact a misnomer. Whilst the specification for 5.25 inch floppy discs employs Imperial units, the later specification for the smaller floppy discs employs metric units.

The standards for these discs are ISO/IEC 8860-1:1987 (double density), ISO/IEC 9529-1:1989 (high density) and ISO 10994-1:1992 (extra-high density); all of which specify the measurements in metric. These standards explicitly give the dimensions as 90.0mm by 94.0mm.

In most countries, the national standard is simply derived from the ISO standard. In the U.S., however, the applicable standard is instead ANSI X3.171-1989. That, too, specifies the measurements in metric, though. It specifies the catridge dimensions as 90.0mm by 94.0mm by 3.3mm and the diameter of the magnetic disc material itself as 85.80mm.

If you have a floppy disc catridge that does not measure 90mm, then you have one manufactured by someone that is not careful about manufacturing tolerances. (And you should beware. If their product isn't up to specification in one area, it may not be so in others.) If the disc measures 3.5 inches, then it is the wrong size. 90.0mm is 3.5433 inches.

� Copyright 2003-2003 Jonathan de Boyne Pollard. All rights reserved. "Moral" rights asserted.
Permission is hereby granted to copy and to distribute this web page in its original, unmodified form as long as datestamp information is preserved.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
----- Original Message -----
From: "J. Ward" <[EMAIL PROTECTED]>
To: "U.S. Metric Association" <[EMAIL PROTECTED]>
Sent: Monday, 2004-04-05 16:39
Subject: [USMA:29446] Re: USMA digest 1568 - floppies really are 3.5 in. on one side

> I believe that the statement that 3.5 inch floppy disks "are metric" refers to
> the standard that defines floppy disks.  I don't know where to find the
> standard, but all the manufacturer's pages I can find all give the following
> for the case outer dimensions:  94 x 90 x 3.3 mm.  None of them given any
> dimension in inches under the specifications.
>
> It's not surprising that the actual disks be narrower than the nominal 90 mm. 
> This sort of thing is common in engineering and manufacturing.  For example,
> screws are almost always SHORTER than their nominal length, and holes are
> normally DEEPER than their nominal depth.  It's just a way to make sure the
> parts fit together.
>
> Has anyone found / checked the actual governing standard?
>
> John
>
> On Monday 05 April 2004 11:28, Gavin Young wrote:
> > I don't understand why people say that a 3.5 inch floppy is not really 3.5
> > inches. When I measure my floppy disks to the nearest 1/32 of an inch, the
> > dimentions are 3 1/2 in. by 3 5/8 inches. Thus one side is truly 3.5
> > inches. Some prometric websites say that instead of 3.5 inches it is really
> > 90 mm, however my disks measure 89 mm x 93 mm. It is the opening to the
> > floppy drive bay that is 90 mm wide (the disk has to be slightly smaller or
> > else it won't slide into the drive)! Prometric people need to get the facts
> > straight if they are to be credible to nonmetric people.
>
>

Reply via email to