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

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.



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 - Stephen Fuld
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