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From: Bob Eager <news0009@eager.cx>
Newsgroups: comp.misc
Subject: Re: Emigration from Usenet [was: Re: PTD was the most-respected of
 the AUE regulars ...]
Date: 8 Aug 2024 20:45:38 GMT
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On Thu, 08 Aug 2024 22:24:30 +0200, D wrote:

>> It's the thing that holds the address of the current instruction being
>> executed.
>>
>> Effectively, CPU's operate like this loop here
>>
>>  int pc=0; while (1) {
>>    execute_instruction (pc);
>>    pc++;
>>  }
>>
>> After that, 'execute_instruction' can be thought of as a big
>> conditional statement that actually performs the task -- moving data
>> between CPU registers, reading from RAM, whatever.
>>
>>
>>
> Could it have been called instruction counter on some platforms? My
> memory is very hazy but I vaguely remember a register you could
> manipulate directly from my assembler labs and the long gone days when I
> thought computer viruses were interesting.

Instruction counter, to me, is something different. On the ICL 2900, it 
literally counts the number of instructions executed. It can be used 
instead of (or as well as) an interval timer, for scheduling.

The NCR/Elliott 4100 machines called the PC the S register (for Sequence 
register).




-- 
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