3 Apr
1998
3 Apr
'98
2:01 p.m.
On Apr 2, 22:15, Ed G. wrote:
You have to realize that disk storage on mainframe systems in the
1960's was usually quite small. Almost all "large-scale" processing
was from tape drive(s) to tape drive(s). If you find a really good
reference on sorting and collating (Knuth, for example) a lot of
effort is made on doing things with as little core and disk space
as possible. Most of these methods are still used today on really
large data sets (for example, FFT's on multi-gigabyte data sets
which are never entirely in memory.)
DECtape was very much different from other tape media of the time.
You didn't treat it as a disk in just some ways, you treated it as
a disk in all ways.
At the time of DECtape, the most inexpensive removable disk media was
the RK05 DECpack, which cost about $150-$200 per platter. DECtape was
created as a more affordable "disk-like" removable media so that
each user could carry his files around with him.
A 1600 bpi 2400 foot 9-track holds about 40 Megabytes if you use long
blocks. Other more recent magtapes (i.e. DLT's) hold 40-100 Gigabytes per
reel/cartridge. Some specialized optical tape media hold Terabytes
per reel.
But in the 9-track world at least, 800 BPI was always NRZI, 1600 BPI
(and 3200 BPI) was always PE, and 6250 BPI was always a specific type
of GCR.
In the 7-track world, recording was almost always NRZI. One manufacturer
did make a 7-track PE system, but it was never a standard.
Tim.
Received: (from major@localhost)
by minnie.cs.adfa.oz.au (8.8.5/8.8.5) id AAA18630
for pups-liszt; Sat, 4 Apr 1998 00:00:54 +1000 (EST)
X-Authentication-Warning: minnie.cs.adfa.oz.au: major set sender to
owner-pups(a)minnie.cs.adfa.oz.au using -f
Subject: Re: What's magtape good for anyway?
Was dectape an attempt to remedy some of these
problems? My
hazy recollection was that you could treat dectape in some ways as if
it were a disk.
Yes, in the sense that you could perform random-access operations on it. I
used a PDP-8 that had twin DECtape instead of disks. It supported 4(?)
teletypes in a multi-user environment. But DECtape was not 1/2" tape, nor did
it use reels like the ones that later became standard.
How much data can magtape hold? If magtape was a
portable media,
does that mean that the manufacturers agreed on the width of
the tape, the density of recording, the method of recording bits,
etc.?
Yes to all of those, though there are three standard recording densities
(80bpi, 1600bpi, 6250bpi) and several recording methods (NRZ, NRZI, PE, etc).
There are different standard lengths too: 600' 1200' 2400'.
I have an old 9 track tape from a computer course I
took in 1980.
For sentimental reasons I'd love to get a copy of its contents. Is
this possible do you think?
Shouldn't be hard, unless it's suffered from print-through after 18 years.
It's probably 800bpi (NRZI) or 1600bpi (PE). Whether you can understand the
contents depends on the format of the data, of course.
--
Pete Peter Turnbull
Dept. of Computer Science
University of York
Received: (from major@localhost)
by minnie.cs.adfa.oz.au (8.8.5/8.8.5) id XAA18540
for pups-liszt; Fri, 3 Apr 1998 23:50:27 +1000 (EST)
X-Authentication-Warning: minnie.cs.adfa.oz.au: major set sender to
owner-pups(a)minnie.cs.adfa.oz.au using -f
From Tim Shoppa <shoppa(a)alph02.triumf.ca> Fri Apr
3 23:50:14 1998
Received: from alph02.triumf.ca (alph02.Triumf.CA [142.90.114.18])
by minnie.cs.adfa.oz.au (8.8.5/8.8.5) with SMTP id XAA18535
for <pups(a)minnie.CS.ADFA.OZ.au>; Fri, 3 Apr 1998 23:50:19 +1000 (EST)
Received: by alph02.triumf.ca; id AA00796; Fri, 3 Apr 1998 05:50:14 -0800
From: Tim Shoppa <shoppa(a)alph02.triumf.ca>
Message-Id: <9804031350.AA00796(a)alph02.triumf.ca>
Subject: Re: What's magtape good for anyway?
To: pups(a)minnie.cs.adfa.oz.au
Date: Fri, 3 Apr 1998 05:50:14 -0800 (PST)
In-Reply-To: <199804030315.WAA06617(a)renoir.op.net> from "Ed G." at Apr 2,
98 10:15:08 pm
X-Mailer: ELM [version 2.4 PL22]
Content-Type: text
Sender: owner-pups(a)minnie.cs.adfa.oz.au
Precedence: bulk
Mag tape has
several things that make it difficult, one is old (late 60s and through
In old movies, filmmakers often focused on spinning tape
drives when they wanted to show a computer "thinking." What is it
about tape drives that made them such a powerful symbol for big,
complicated computer systems? the 70s)
drives had a difficult time starting and stopping without
breaking tape or resorting to complex(then standards) controllers. This
lead to things like large interrecord gaps (start, speed up read, stop,
backspace records, stop, read) due to the inerta of starting and stoping
the reels. Also fixed record sizes were used to make blocks about the
same length so blocks and marks could be differentiated using simple
timers.
Was dectape an attempt to remedy some of these problems? My
hazy recollection was that you could treat dectape in some ways as if
it were a disk. Magtape was
for the longest time the only portable media, which lead to
the ansi/EBCDIC problems (Evryone else and IBM/HP). It was generally
used for archival storage making file organized access excess overhead.
While often used as block oriented, many systems used it more as a stream
device where the high volume storage (relative to the disks of the time)
capability was available.
How much data can magtape hold? If magtape was a portable media,
does that mean that the manufacturers agreed on the width of
the tape, the density of recording, the method of recording bits,
etc.?
Absolutely. There are ANSI standards for all of the above. Despite
what others claim, interchangability was always rather straightforward,
and the worst problems are the "concepts" not supported by some operating
systems (i.e. Unix lacks file support for anything other than a file that's
just a stream-of-bytes).
I have an old 9 track tape from a computer course I
took in 1980.
For sentimental reasons I'd love to get a copy of its contents. Is
this possible do you think?
Absolutely. Part of my current profession is reading 9- (and 7-) tracks
that are up to 35 years old.
> When processing was done on early system usually
two or three drives were
> involved as one of two were for reading and the third was writing results
> usually due to memory size limitations of the time compared to the amount
> of data. Alot of magtapes lore is a result of historical use.
These uses aren't just historical - many of us still deal with datasets
that are Terabytes in size and which cannot be disk (or core) resident.
Tim. (shoppa(a)triumf.ca)
Received: (from major@localhost)
by minnie.cs.adfa.oz.au (8.8.5/8.8.5) id XAA18575
for pups-liszt; Fri, 3 Apr 1998 23:55:45 +1000 (EST)
X-Authentication-Warning: minnie.cs.adfa.oz.au: major set sender to
owner-pups(a)minnie.cs.adfa.oz.au using -f
From Tim Shoppa <shoppa(a)alph02.triumf.ca> Fri Apr
3 23:55:06 1998
Received: from alph02.triumf.ca (alph02.Triumf.CA [142.90.114.18])
by minnie.cs.adfa.oz.au (8.8.5/8.8.5) with SMTP id XAA18565
for <pups(a)minnie.CS.ADFA.OZ.au>; Fri, 3 Apr 1998 23:55:32 +1000 (EST)
Received: by alph02.triumf.ca; id AA32661; Fri, 3 Apr 1998 05:55:06 -0800
From: Tim Shoppa <shoppa(a)alph02.triumf.ca>
Message-Id: <9804031355.AA32661(a)alph02.triumf.ca>
Subject: Re: What's magtape good for anyway?
To: pete(a)dunnington.U-NET.com
Date: Fri, 3 Apr 1998 05:55:06 -0800 (PST)
Cc: pups(a)minnie.cs.adfa.oz.au
In-Reply-To: <9804031301.ZM14090(a)indy.dunnington.york.ac.uk> from "Pete
Turnbull" at Apr 3, 98 12:01:48 pm
X-Mailer: ELM [version 2.4 PL22]
Content-Type: text
Sender: owner-pups(a)minnie.cs.adfa.oz.au
Precedence: bulk
How much data
can magtape hold? If magtape was a portable media,
does that mean that the manufacturers agreed on the width of
the tape, the density of recording, the method of recording bits,
etc.?
Yes to all of those, though there are three standard recording densities
(80bpi, 1600bpi, 6250bpi) and several recording methods (NRZ, NRZI, PE, etc). From Tim Shoppa <shoppa(a)alph02.triumf.ca> Sat Apr
4 00:00:44 1998
Received: from alph02.triumf.ca (alph02.Triumf.CA [142.90.114.18])
by minnie.cs.adfa.oz.au (8.8.5/8.8.5) with SMTP id AAA18625
for <pups(a)minnie.CS.ADFA.OZ.au>; Sat, 4 Apr 1998 00:00:48 +1000 (EST)
Received: by alph02.triumf.ca; id AA23631; Fri, 3 Apr 1998 06:00:44 -0800
From: Tim Shoppa <shoppa(a)alph02.triumf.ca>
Message-Id: <9804031400.AA23631(a)alph02.triumf.ca>
Subject: Re: Bug in Bob Supnik's Emulator!
To: pups(a)minnie.cs.adfa.oz.au
Date: Fri, 3 Apr 1998 06:00:44 -0800 (PST)
In-Reply-To: <199804030750.XAA10664(a)moe.2bsd.com> from "Steven M. Schultz"
at Apr 2, 98 11:50:23 pm
X-Mailer: ELM [version 2.4 PL22]
Content-Type: text
Sender: owner-pups(a)minnie.cs.adfa.oz.au
Precedence: bulk
Not having any great need of an emulated PDP-11
I've not pursued
the (suspected) bug in Bob Supnik's emulator. Even on a PentiumPro
an emulated 11 is slower than a real 11/73 (and a lot slower than an
11/93 - which I should cease neglecting and stuff a SCSI card into
some day as I did with the 11/73).
On a cow orker's 200 MHz Pentium Pro, Bob Supnik's emulator (compiled
with gcc and running under Linux) is about twice as fast as a real
11/73 for most CPU-intensive operations. Speeds for I/O based
operations can range from incredibly faster to incredibly slower
than a real -11, of course, and a lot of the interrupt and device
priority schemes seem seriously out of whack with how a real PDP-11
works. And speed also depends on whether the MMU
is enabled or not, too.
The same emulator running on a 7-year-old 133 MHz DEC Alpha is about
a third the speed of a real 11/73 (slow enough that a lot of 60 Hz
line-time-clock interrupts go uncounted under RT-11, for example!)
Tim.
Received: (from major@localhost)
by minnie.cs.adfa.oz.au (8.8.5/8.8.5) id EAA19270
for pups-liszt; Sat, 4 Apr 1998 04:25:23 +1000 (EST)
X-Authentication-Warning: minnie.cs.adfa.oz.au: major set sender to
owner-pups(a)minnie.cs.adfa.oz.au using -f
9708
days inactive
9708
days old
0 comments
1 participants
participants (1)
-
peteļ¼ dunnington.u-net.com