thinking of the "ultimate" retro x86 PCs - what bits to seek/keep ?

Liam Proven lproven at
Mon Jun 6 10:28:51 CDT 2016

On 6 June 2016 at 17:08, Fred Cisin <cisin at> wrote:
> On Mon, 6 Jun 2016, Liam Proven wrote:
>> And there was never a 720kB IBM standard, only on things like Apricots.
> Could you explain?
> 720K was just as much of an IBM "standard" as 360K.  Starting with PC-DOS
> 3.20, ("/F:2").  Sure, other companies used the same media for different
> formats, but nowhere near as much as 5.25".
> "Convertible", PS/2, optional in and external to AT.

I thought you might chime in on this.

AIUI -- not sure -- the 720 kB *format* was mostly used on 5.25" DS/DD
80-track disks, no?

Apricot and other vendors shipped MS-DOS machines with only 3.5"
DS/DD/80t drives. The same format was the standard diskette type of
the Atari ST, too.

But AFAIK IBM never shipped machines with DS/DD/80t track drives as
standard, did it? *Possibly* as a 2nd drive, but not as the stock. I
thought the IBM PC-compatibles came with:
#1 DS/DD/40t, 5.25", 360 kB (PC, PC-XT etc., 1981)
#2 DS/HD/80t, 5.25", 1.2MB (PC-AT, 1984)
#3 DS/HD/80t, 3.5", 1.4MB (PS/2, 1987)

And finally the not-widely-copied DS/ED/80t 2.8MB drives.

> If a good 150RPM ED drive were to have been readily available, then 2.8M
> could have been retrofitted to all 1.4M systems, including Amiga, etc. But
> would that, and the Barium-Ferrite disks have been worth it for just twice
> the capacity?

Wouldn't they have got much cheaper if every cloner had used them?

The cloners copied the 1.2MB and 1.4MB drives, but not the 2.8 ones.
Was media expense the main problem? Or expensive FDC chips? Or both?

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