Orchid XP v8 <voi### [at] devnull> wrote:
> >> So the concept of a filesystem storing named files already existed at
> >> this time?
> >
> > Generally, yes. But you usually wound up pre-allocating files, and they
> > were contiguous on disk.
>
> OK.
>
> Files only on disk? Or on tape too? (From what I've seen, punch cards
> didn't have this level of abstraction. It wouldn't be terribly necessary
> I guess...)

Data on punch cards are treated no differently than data on mag tape, paper tape
or disk.  It is a sequential file with a fixed record length of 80 bytes.
A program only knows it reads 80 byte records, it doesn't care what physical
device its on. Just don't try to read the punch card data backwards.

> >> Interesting. So the system actually "knows" where each field of a
> >> record is then?
> >
> > Records were fixed size, so it was trivial to calculate.
>
> OK. But does the system know where the *fields* in a record are? Or just
> what size the records are?

The file systems does not understand fields.  It understands file organization
(sequential, indexed, random access), record type (fixed, variable, undefined),
and maximum record length and block size.  Interpretation of data at the field
level is done by the program.  If the file is a part of a database, the database
manager handles field definition.

>
> >> Really? I didn't think anybody had mainframes any more... just big
> >> server farms.
> >
> > The people who want to do lots of I/O have machines where instead of
> > GPUs they have IOPs.  A 800,000 line phone switch, for example, is
> > pretty much all IOP, with something like a 68000 running the actual
> > switching part.
> >
> > Of course, what one might call a "PC" nowadays has a terabyte of RAM and
> > 96 quad-core processor chips, so the lines blur.
>
> Yeah, I think the term "mainframe" is probably obsolete now. There are
> probably more exact ways to describe what type of computer you mean.
>

There is a lot of overlap between a "mainframe" and a "PC". There are some PC
configurations that are more powerful than some mainframes.  So what is or is
not a mainframe can be debatable. There are very few things a modern mainframe
can't do that a PC can and vice versa.  You can run Linux on an IBM z/series
machine, just like on a PC.  As a user it would be difficult to tell the
difference.  Its all a matter of scale.

> --
> http://blog.orphi.me.uk/
> http://www.zazzle.com/MathematicalOrchid*

Isaac

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