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

On Tue, 25 Jun 2024 08:49:43 +0200
Terje Mathisen <terje.mathisen@tmsw.no> wrote:

John Levine wrote:

According to Lawrence D'Oliveiro  <ldo@nz.invalid>: 

How much of theoretical disk bandwidth was the filesystem capable
of using? Because I know early Unix systems were pretty terrible
in that regard, until Berkeley’s “Fast File System” came
along. 

 
My recollection is that if you were using QSAM with multiple buffers
and full track records it wasn't hard to keep the disk going at full
speed. Later versions of OS do chained scheduling if you have enough
buffers, doing several disk operations with one cnannel program. 

 
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.
>

I am not sure that "saturate the hard drive" is a correct wording.
According to my understanding, [when within track] hard drives used in
early PCs were more capable than hard disk controllers (Xebec 1210 in
XT, I don't know what was used before XT). In turn, disk side interface
of disk controller was likely more capable than its system bus side.
Now, those are just feelings, I can't find hard data to back it up.

I did end up making special file/record layouts which were optimized
for this, using exactly 4kB for each header+bitmap record.
 
Terje