zlacker

[return to "1 kilobyte is precisely 1000 bytes?"]
1. kmm+rb[view] [source] 2026-02-03 17:41:38
>>surpri+(OP)
And a megabyte is depending on the context precisely 1000x1000=1,000,000 or 1024x1024=1,048,576 bytes*, except when you're talking about the classic 3.5 inch floppy disks, where "1.44 MB" stands for 1440x1024 bytes, or about 1.47 true MB or 1.41 MiB.

* Yeah, I read the article. Regardless of the IEC's noble attempt, in all my years of working with people and computers I've never heard anyone actually pronounce MiB (or write it out in full) as "mebibyte".

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2. pwdiss+sL[view] [source] 2026-02-03 20:04:04
>>kmm+rb
> classic 3.5 inch floppy disks

90 mm floppy disks. https://jdebp.uk/FGA/floppy-discs-are-90mm-not-3-and-a-half-...

Which I have taken to calling 1440 KiB – accurate and pretty recognizable at the same time.

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3. skissa+eo2[view] [source] 2026-02-04 07:44:28
>>pwdiss+sL
> 90 mm floppy disks. https://jdebp.uk/FGA/floppy-discs-are-90mm-not-3-and-a-half-...

That page is part right and part wrong.

It is right in claiming that "3.5-inch" floppies are actually 90 mm.

It is wrong in claiming that the earlier "5.25-inch" floppies weren't metric

"5.25-inch" floppies are actually 130 mm as standardised in ECMA-78 [0]

"8-inch" floppies are actually 200 mm as standardised in ECMA-69 [1]

Actually there's a few different ECMA standards for 130 and 200 mm floppies – the physical dimensions are the same, but using different recording mechanisms (FM vs MFM–those of a certain age may remember MFM as "double density", and those even older may remember FM as "single density"), and single-sided versus double-sided.

[0] ECMA-78: Data interchange on 130 mm flexible disk cartridges using MFM recording at 7 958 ftprad on 80 tracks on each side), June 1986: https://ecma-international.org/publications-and-standards/st...

[1] ECMA-69: Data interchange on 200 mm flexible disk cartridges using MFM recording at 13 262 ftprad on both sides, January 1981: https://ecma-international.org/publications-and-standards/st...

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