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GeneralRe: Tabs Pin
Richard MacCutchan3-Mar-20 22:18
mveRichard MacCutchan3-Mar-20 22:18 
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lw@zi 3-Mar-20 22:27
professional lw@zi 3-Mar-20 22:27 
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Richard MacCutchan3-Mar-20 22:56
mveRichard MacCutchan3-Mar-20 22:56 
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Member 79891224-Mar-20 2:32
MemberMember 79891224-Mar-20 2:32 
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Richard MacCutchan4-Mar-20 2:50
mveRichard MacCutchan4-Mar-20 2:50 
GeneralRe: Tabs Pin
Member 79891224-Mar-20 3:12
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Richard MacCutchan4-Mar-20 3:31
mveRichard MacCutchan4-Mar-20 3:31 
GeneralRe: Tabs Pin
Member 79891224-Mar-20 5:02
MemberMember 79891224-Mar-20 5:02 
Then you may know the one-operand infinite loop of 1108 - it didn't even take the whole of an instruction to create an infinite loop.

I don't remember all the details of Univac addressing formats, so this description may not be a 100% exact: You could set a bit in the address field for one extra level of indirection - in the location given, you won't find the data, but the address of the data. There you might find another address with the indirection bit set. Any levels of indirection was allowed, all executed as part of the operand value decoding. If you set up one such indirection pointing to itself, you had a single operand version of an unconditional jump to itself.

Only that while decoding that indirection, the CPU didn't respond to interrupts. A single-instruction loop could be broken, e.g. by the system operator. The single-operand loop totally locked up the entire CPU; it had to be rebooted - which, for a Univac 1100 system was something more than Ctrl-Alt-Del Smile | :) .

Most graduate, "responsible" students were aware of this quick way of taking the system down, but everyone tried to keep it secret to the younger, and potentially less responsible, student who might want to "try it out for fun".

The U had an old 1108 and a new 1110. I don't think the 1110 went down many times (if at all) from one-operand infinite loops. It could be that Univac had made it interruptible on the 1110, or it could be that my generation of students never did assembly programming on the Univac; we were on our way into the OO world (beliving that Simula would forever be The superhero of OO languages...). Very few of my fellow students ever saw the U1100 instruction set and addressing modes at all.
GeneralRe: Tabs Pin
Richard MacCutchan4-Mar-20 5:12
mveRichard MacCutchan4-Mar-20 5:12 
GeneralRe: Tabs Pin
  Forogar  4-Mar-20 3:53
professional  Forogar  4-Mar-20 3:53 
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Dan Neely4-Mar-20 3:26
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Member 79891224-Mar-20 4:41
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Fever9055-Mar-20 3:44
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Stefan_Lang4-Mar-20 21:32
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KLSmith5-Mar-20 5:15
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Kirk 103898216-Mar-20 3:59
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BillWoodruff3-Mar-20 22:29
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Greg Utas4-Mar-20 1:35
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W Balboos, GHB4-Mar-20 1:39
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Member 79891224-Mar-20 2:51
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GeneralRe: Tabs Pin
W Balboos, GHB4-Mar-20 5:08
mveW Balboos, GHB4-Mar-20 5:08 
GeneralRe: Tabs Pin
Member 79891224-Mar-20 12:25
MemberMember 79891224-Mar-20 12:25 
GeneralRe: Tabs Pin
Richard MacCutchan4-Mar-20 2:54
mveRichard MacCutchan4-Mar-20 2:54 
GeneralRe: Tabs Pin
Greg Utas4-Mar-20 3:08
professionalGreg Utas4-Mar-20 3:08 
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Richard MacCutchan4-Mar-20 3:34
mveRichard MacCutchan4-Mar-20 3:34 

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