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From: Michael S <already5chosen@yahoo.com>
Newsgroups: comp.arch
Subject: Re: ancient OS history, ARM is sort of channeling the IBM 360
Date: Tue, 25 Jun 2024 11:19:04 +0300
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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>: =20
> >> 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=C3=A2=E2=82=AC=E2=84=A2s =C3=A2=E2=82=
=AC=C5=93Fast File System=C3=A2=E2=82=AC=C2=9D came
> >> along. =20
> >=20
> > 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. =20
>=20
> Even on (MS)DOS it was easy to saturate the hard drive from a single=20
> 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.
>=20
> Terje
>=20