But AFAIK IBM
never shipped machines with DS/DD/80t track drives as
standard, did it?
Of course they did. PS/2 8530.
Oops. And the 5140
"Convertible".
Interesting. I did not know that!
Those were machines with 3.5" 720K as the only internal drives.
Possibility of other kinds of drives externally.
But, 3.5" 720K drives became available at that time (PC-DOS 3.20) as
external drives and/or as internal for 5150/5160/5170.
Soon thereafter (PC-DOS 3.30), 1.4M drives became available on machines
with a 500K bits per second data transfer rate (coincidentally all IBM
machines with 80286 and above processors). For machines that could take
the 1.4M drives, few chose to get the more limited, but almost the same
price, 720K drives.
Therefore, the reign of 720K was non-IBM laptops (mostly since MS-DOS
2.11) before 1.4M, throughout the market during IBM PC-DOS 3.20, and then
only the remaining 8088/8086 machines from 3.30 on.
Easy enough to have missed their short-term domination of the market if
you happened to have been on holiday.
I was waiting at the door of the Oakland IBM store on the day that PC-DOS
3.20 was released.
