Weekly Classic Computer Trivia Question (20141205)

Fred Cisin cisin at xenosoft.com
Sat Dec 6 14:38:28 CST 2014

> > Consider also the infamous 1.44MB disk.  That number comes from 1440 * 1024, so
> > apparently a megabyte is *also* 1,024,000 bytes.  If we can humpty-dumpty it
> > and pluck numbers out of the air, why not just call a megabyte 3,141,592 bytes?

On Sat, 6 Dec 2014, Johnny Billquist wrote:
> Actually, the 1.44MB floppy holds 1,474,560 bytes.
> 512 bytes per sector, 18 sectors per track, 80 tracks per side, and two
> sides... Where did you pull the 1440*1024 from???

1,474,560 IS, indeed 1440 * 1024
If you use powers of 10, it would be 1.47 M.
If you use powers of 2, it would be 1.40624 M.

SO, how did they get "1.44 M"?
(rhetorical question; don't you hate rhetorical questions?)

In order to get "1.44", they stated that it was 1440 Kilobytes, (where
"kilobyte" was the traditional COMPUTER meaning of 1024.
Then they divided 1440 by 1000, to get 1.44.
They defined "Megabyte" to be 1000 kilobytes (1024)!

Therefore, they divided by 1024 AND divided by 1000.

You can make a case for powers of 10;
you can make a case for powers of 2;
it takes marketing assholes to mix them.

If you round to "1.4 M", then at least it doesn't pin the needle on the

The ST506, when formatted with 512 byte sectors, was 306 * 2 * 17 * 512
for 5326848   5326Ksi  5202Kibi  5.33Msi  5.08007815Mebi
The ST412, when formatted with 512 byte sectors, was 306 * 4 * 17 * 512
for 10653696  10653Ksi 10404Kibi  10.4 Msi  10.16015625 Mebi

In those days, the rounding wasn't a big problem, and either set of units
would do.

NOTE:  In contrast with modern marketing, Seagate did NOT try to
"maximize" the numbers by changing units nor using extraneous
"significant" digits.
They called the 506 a "5 Megabyte drive", NOT "5.33" nor "5.08".
They called the 412 a "10 Megabyte drive", NOT "10.4" nor "10.16".
'course part of that was the higher prevalence of bad sectors.
If'n you buy a "10.4 Megabyte" drive and it ends up formatting to 10.2
(due to some bad sectors), you gripe about the quality.
OTOH, if you buy a "10 Megabyte drive", and it formats to 10.2, then you
brag to all of your friends about what a great drive you got.
(and Seagate gets a better reputation)
[for some value of indeterminate "you", not speaking to Eric or Tony]

Grumpy Ol' Fred     		cisin at xenosoft.com

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