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From: Lawrence D'Oliveiro <ldo@nz.invalid>
Newsgroups: comp.arch
Subject: Re: ancient OS history, ARM is sort of channeling the IBM 360
Date: Tue, 25 Jun 2024 05:39:28 -0000 (UTC)
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On Tue, 25 Jun 2024 04:04:31 -0000 (UTC), 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.

Presumably the downside of that was there was no such thing as “stream-
oriented” I/O: it was all record-based, just like most of the other OSes.

Unix was unique in hiding the need from applications/users to worry about 
sector sizes when writing to files and reading from files. But there was a 
significant overhead in that, at least in the early years.