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

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 did end up making special file/record layouts which were optimized for this, using exactly 4kB for each header+bitmap record.
Terje
--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"