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From: "Stephen Fuld" <SFuld@alumni.cmu.edu.invalid>
Newsgroups: comp.arch
Subject: Re: ancient OS history, ARM is sort of channeling the IBM 360
Date: Tue, 25 Jun 2024 14:54:28 -0000 (UTC)
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Lawrence D'Oliveiro wrote:

> 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.

For the business oriented and even scientific oriented applications
typically run on S/360, "stream oriented" I/O would have been a
distinct disadvantage.  COBOL I/O (and even Fortran I/O) is "record
oriented".  "byte oriented" I/O would ha made things harder for the
programer as well as much less efficient.

 
> 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.


There still is additional overhead.  But the application amd
programming language mix has changed, so stream oriented I/O is now the
default.



-- 
 - Stephen Fuld 
(e-mail address disguised to prevent spam)