Here's what happens when an 18 year old buys a mainframe...

Jon Elson elson at
Wed Mar 30 12:11:03 CDT 2016

On 03/30/2016 10:51 AM, William Donzelli wrote:
>> Somebody mentioned a house with a collapsed floor.  A friend of mine bought
>> two 770/145s and a GE/Intersil memory box.  (I bought the other memory box,
>> in 1979 or so, a **MEG** of memory was a big deal!)
> I assume you mean 370/145s/
>   Whatever happened to them? In 1979, they
> would have been still usable machines.
Well, the problem with the 370's were peripherals and power. 
Although the lower level 370's had integrated channels, you 
still needed control units and drives.  To do any real work, 
you'd need at least a DASD controller and drives and a com 
controller.  Probably at least a tape controller and one 
drive to do backups and load software.  That won't fit in 
the bedroom of a 2-bedroom house, which was where this thing 

Second was the 370s used a motor alternator set to convert 
50/60 Hz power to 415 Hz power.  To keep compatibility, they 
used the same size MG set for a range of machines.  So, the 
145 had a 17 KVA output alternator with a 20 Hp 208V 3-phase 
motor.  We tried to build a phase converter to run the motor 
off the guy's 60 A 240 V service, but the reactive current 
was over 60 A and would blow the main breaker.  The main 
logic supply for the /145 was 390 A at +1.3 and -3 V, so 
about 1.5 KW.  We should have just got a bunch of big 5V 
switcher supplies and tuned them down to the appropriate 
voltage.  But, that would have likely cost more than he paid 
for the machines, maybe even surplus.

The 145 was not a real high performance machine.  Although 
the memory was 64 bits+parity wide (for ECC) the main data 
path was only 16-bits wide, and the microcode word was 
rather vertical, so while 360/50 and 360/65 could execute 
simple instructions in about 4 microcode cycles, the /145 
took something like 7+.  A 32 bit add register to register 
was 1.4 us, add memory to register was 2.4 us. Floating 
point divide was 28 us (short) or 88 us (long).


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