[geeks] Emulation versus replication

Tue Sep 9 05:57:18 CDT 2003

I moved this to the geeks list as I think this thread belongs here.

As we were discussing replicas of old technology, in specific the Apple 1,
I'd like to disucss emulating old computers as opposed to replicating them.

Since I never got involved with DEC computers, I'll use IBM mainframes of
the 70's and 80's as a discussion point. To be exact, the one at
Uni-Col Corporation where I worked in 1979-1980.

The typical setup of a mainframe at the time, was big on i/o and small
on processing. A very large system of 1979 would be two 370 168's (about
2 MIPs each) connected together as an asymetric multiprocessor system, 
(different I/O on each). with core (actually it was ram by those days)
of 2 to 3 meg on each processor. 

The system could be split and run as two seperate systems. It would fill
my current apartment.

I don't remember the exact configuration, but here is a rough guess:

1 2501 card reader (1000 cpm)
2 1403n1 line printers (1000 lines per minute chain printers)
1 140? card reader and punch. (reads or punches but not both)
1 ??? combination card reader and punch (read a card, punch new data and 
	print on it.)
2 tape controlers connected to both machines
14 3420 9 track 6250 bits per inch tape drives.
2  3240 7 track tape drives.
1 2305 5 megabyte fixed head disk drive.
4 Disk drive controlers connected to both machines
32 3330-II drives 200 megabytes each.
Several 3270 controllers (32 3270 crt terminals on each)
32 line sync/asnc tty controler.

It ran IBM MVS 3.8 and JES2, and TSO. There was also some propritary time
sharing system running, but it was slowly fading away. 

At that time MVS etc, were free as there as no competition for the hardware.

So now let's look at it if it were modern harware.

I'll start with I/O first.

The main thing is the disk drives. The entire farm of disk drives
can be replaced with on 6 gigabyte disk. If we wanted speed over price,
we could split it into 4 ide drives placing 8 disk images on each drive.
Even with relatively slow IDE drives, they would be faster than the
3330-II's. 

I'd love to have the 3330-II's, the room to keep them and the money to
air condition and run them. Not very likely on my budget.

Fixed head disk: a 5 megabyte ram disk would do the job and cost
pennies today. 

Tape drives: QIC-150 or QIC-60 tape drives would do fine. Seven of them
on a SCSI controler would emulate the setup pretty well, Two controlers
with 14 drives would be just right. 

Line printers: Definately a thing of the past. A 20 ppm laser printer
would replace them nicely.

Card readers: Sorry all my card decks disapeared about 15 years ago. :-(

Card puch:    Same thing. Can anyone still buy card stock?

3270 controlers. At this point it's easy to replace them with TCP/IP and
		tn3270. One or two 100mbit ethernet cards would be enough.
		For the truely 3270 addicted, there are 3274's with TCPIP
		support, though they would be hard to find.

Communications lines: better handled via TCP/IP, but a 32 port serial card
is not hard to find for async, sync is more difficult.

So now the question is how do we get a processor and what do we interface
it to? IBM mainframes used a propritary paralell device structure using
two cables called bus and tag. If we were to get a mainframe of any sort,
we would need the bus and tag interface on the devices so that we would be
stuck with the entire setup.

Meanwhile we could run the mainframe as an emulated computer on a PC compatible
computer. There is a IBM mainframe emulator called hercules. It runs
under windows and Linux on PC compatibles. Since it is open source, it also
has been ported to Alpha and SPARC.

Now this is an interesting dilema to me. I can't afford a "shrine" to a 
mainframe, but I can afford an old PC. To me the "look and feel" of a 
mainframe is special. Just sitting in a room full of computer, or a DASD
(disk drive) farm alone in a darkend room with 100 disk drives the size of
a washing machine is special. 

A room full of racks wether they are PC's or Sun's or whatever just dosen't
feel right. It seems to be a room full of toys to me.

So without the room itself, I'd end up sitting at my PC thinking that
it's a 3270 connected to a far off mainframe. Not as satisfying, but
it might work anyway.

Emulation is not new to me or to IBM computers. The IBM 360-370-390
systems were "microcoded" from the first. The original 360, the 360
model 30 (360/30) was microcoded using mylar punched cards. I once saw
them, but never actualy owned any. The later machines such as the 370
series booted from 8inch floppies and later internal hard drives.

The last hard coded IBM mainframe, the IBM 1401 series (1960-1963) could
be emulated by loading a card deck into the 360/30. It then became a
real 1401 and temporarily lost its 360 identity. Later versions of the
emulator ran under operating systems and my last brush with a 1401
emulator was in 1979 on a 370/168 running MVS.

Due to internal politics at Xerox, the only way they could get on what
was the precoursor of the internet in 1970 was to emulate a PDP-10 on
a Xerox Data Systems (formerly SDS) 940. Nice machine, I used one as a
SDS940 in 10th grade.

Now here comes the big problem for me. The operating system of choice for
me on these beasts is VM/370. VM let you run in a "virtual machine". You
IPL'ed (booted) your own operating system. You could boot MVS, VS/1, DOS
or any combination as long as you had enough memory and disk space. 

You could even get VM one to run with 95% of the performance on a real
machine. Single users at terminals normaly would run an operating system
called CMS (conversational monitor system). 

I have two problems with this setup. MVS, VS/1 or DOS were primarily batch
operating systems. For example, under DOS on a smaller machine (370/145,
324k,8 3330-I (100 meg)) a previous employer of mine ran among other things
payroll for 30,000 employees. 

I don't have 30,000 employees, I don't have 1 employee at the moment,
I don't really know what else to do with it expect have it for nostalgia.

The other problem is that just after releasing VM/370 release 6, the
last free one IBM dropped VM. The result was a disaster for IBM and a 
good deal for DEC. 

Since the entire VM system was open source, people had been publishing
mods for it for years. IBM had been ignoring them. After much hair
pulling at IBM and threats of customers migrating to DEC, IBM changed
their direction.

They took the mods that had been floating around, and incorporated them
into the operating system, called it the VM System Product (VM/SP) and
charged a monthly license fee. A quantum leap in useability was the 
inclusion of a previously unpublised editor called Xedit. 

Xedit was the VM equivalent of Vi. Previously you had a full screen editor,
but you had to use up and down commands, and edit to bring the one line
you could edit at a time into the "input area" for editing. A quantum leap
from punched cards (going from cards to edit cut 3-4 hours off of a night
at one employer of mine), but painfully slow to me.

So far, AFIK, no one has written an Xedit clone, nor has IBM opened it up
even to experimentors or hobbyists.

So to me it's all doable as an emulator, but I feel all dressed up with no
place to go. :-(

Any thoughts?

Geoff.

-- 
Geoffrey S. Mendelson gsm at mendelson.com 972-54-608-069
Icq/AIM Uin: 2661079 MSN IM: geoffrey_mendelson at hotmail.com (Not for email)
Carp are bottom feeders, koi are too, and not surprisingly are ferrets.