Re: ancient OS history, ARM is sort of channeling the IBM 360

Lawrence D'Oliveiro wrote:

On Tue, 25 Jun 2024 08:49:43 +0200, Terje Mathisen wrote:
 

Even on (MS)DOS it was easy to saturate the hard drive from a single
program, you just needed large enough (i.e. at least a full track each)
buffers.

 That sounds more like a peak thing than a sustained thing. In between
filling the buffers, the disk is left idle. So on average you are
operating well below theoretical disk capacity.

What I measured was very close to the disk vendor's max spec for reading or writing the entire disk. Maybe they were a little bit more efficient than you imply, i.e. just a little bit of read-ahead caching would cover the latency between read requests. That said, I never measured the sustained write speed directly, only indirectly by the time it took PartitionMagic to restore an image or copy a disk.

 After all, MS-DOS never suppported async I/O.
 

Not by the OS, no, but I certainly wrote asm code which used hybrid interrupt/polling to sustain max IO rate background transfers for both network and serial/parallel ports.
Terje
--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"