Why the MS-DOS floppy disk cache was valid 2 seconds…

If you’re old enough to have used MS-DOS you know the benefits a read cache introduced back at the time for floppy disks. Without such a cache everything data intensive was magnitudes slower.

Now after all these years more and more stories emerge about how certain thresholds and timeings where set back in the days.

This is such a story:

Mark Zbikowski led the MS-DOS 2.0 project, and he sat down with a stopwatch while Aaron Reynolds and Chris Peters tried to swap floppy disks on an IBM PC as fast as they could.

They couldn’t do it under two seconds.

So the MS-DOS cache validity was set to two seconds. If two disk accesses occurred within two seconds of each other, the second one would assume that the cached values were still good.

Raymond Chen blog

There are more links in the original article – so go there and down that rabbit hole!

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