From: lithgow@uslp.UUCP
Newsgroups: comp.sys.acorn
Subject: Re: help! checkmap fails
Date: 6 Apr 92 09:22:53 GMT
Article-I.D.: ucbvax.9204061129.AA28250

This is getting to be a habit. :-)

[In message "Re: help! checkmap fails", Philip R. Banks writes:]
>steve@acorn.co.uk (Steve "daffy" Hunt) writes:
>> banksie@khantazi.welly.gen.nz (Philip R. Banks) writes:
>>> errors are is difficult. This is one thing, is the Arc unique for having the
>>> only filing system that de-fragments *as* it is being used?
>> No, I believe it's common practice.
>
>   You sure? I mean of the types of systems I can think of :-
>
>MS-Dos doesn't de fragment till explicitly told to.
>
>Macs require an explicit instruction to do so. Usually a de-fragmentation
>   program. [...]
>
>Unix does it at reboot time during it's filing system checks.

Unless you're talking about some whacky UNIX like ULTRIX, HP/UX, then
this is wrong. System V, Xenix, SVR4, SCO UNIX, etc., all require special
de-fragmentation programs, which, until recently, have been rare. I
worked with a company that wrote a de-fragmentation program, so I'm
pretty sure of this. The typical method of de-fragmenting a UNIX FS is to
back it up to a streaming device (such as tape), remake it (ie. format
it), and restore it. Yech.

I am almost 100% sure that 95% of the UNIX variants out there, provide
*no facilities* for de-fragmentation. One reason that this apparant
oversight exists, is that fragmentation is not such a big deal for
multi-user systems, since the disk heads are skittering everywhere,
anyway. Not to mention the massive caches these systems have.

Speaking of caches, my ADFSBuffers setting of 256 may have messed PackDir
up -- I'll try it with no ADFSBuffers. (I do have the latest version.)

Does the ADFSDirBuffers setting have the same detrimental effects as
ADFSBuffers? I hope not, because you can't turn it off...

>VMS does only when told to - usually late at night if the SysAdmn has any
>   brains... (It takes ages...)
>
>MVS does it when told to.
>
>Amiga "Whats high speed floppies?" machines again have to be told as far as
>   I know.
>
>And Atari's use MS-Dos style formats...
>
>   As far as I know the Arc is the only machine that does it (on E format of
>course) without being told to and automatically *as* it is being used...
>What systems do you know of that do de-fragmentation under the same
>criteria?

This is one of the things that both delights and frustrates me with
Acorn. An Acorn bod has said, in reference to one of RISC OS's many
innovative features, 'but doesn't everyone do it?'

Imagine this, an Acorn press release:

              PRETTY ORDINARY NEW MACHINE RELEASED

Well, we've just released a new mid-range machine. It's not much,
really.  Despite having a build quality of an Apple or IBM, it's only
about three times as fast, and a third the price of their mid-range
(sorry about that).

It's WIMP interface can only do the boring old standard stuff -- you
know, drag and drop, solid scroll, postscript-style graphics, a fully
integrated multitasking environment including Filer, translucent
networking, etc.

It has build-on-the-fly, anti-aliased, outline fonts (doesn't everyone
have that?), graphics resolution and colour-palette independance, 30KHz
8-bit logarithmic (equivalent to 12-bit linear) stereo sound with eight
channels.

It has four card expansion slots, which accept cards currently available
including high-quality 16bit sound sampling, video-digitisers, fax cards,
laser printer drivers, SCSI cards, IEEE-488, satelite converters,
graphics, ethernet, industrial control, transputers, etc. (Sorry about
the poor range.) Of course, we won't even mention the fact that, with a
well designed card, all you have to do is plug it in and turn the machine
on, and the software will automatically be downloaded from the onboard
ROM, and you'll have no problems with interrupts, I/O memory, or real
memory. After all, didn't everybody design their buses like this?

The OS has been placed in ROM so that you save large amounts of RAM, but
it is possible to overlay bits of it with new modules from RAM, and at
run time. Of course, this forces us to make sure our OS has far less bugs
than those of any of our competitors -- our appologies.

Also, because we are honest lads (rather than two-tounged marketing
oriented types who would sell the Earth as a hyper-computer run by mice if
they could get away with it) we have neglected to announce this machine
until it was definitely available. Our abject appologies for completely
failing to mislead you by, oh, half a year or so.

Anyway, you get the idea.

- Malcolm.

lithgow@usl.com

These opinions are mine. They are also absolutely correct. I think.


--- End of forwarded message from  <lithgow>