Immutability - was Re: ENIAC programming Was: release dates of early microcomputer operating systems, incl. Intel ISIS

Fred Cisin cisin at
Thu Sep 17 16:38:32 CDT 2015

On Thu, 17 Sep 2015, dwight wrote:
> If working on a newer X86 processor, this is necessary, not to protect the
> code but because the code is cashed and my not be updated in time for
> it to be executed.
> Write through is expensive and only provided on the data side, if at all.
> Dwight

On some/most older X86 real mode, a JMP $+2 would flush the prefetch 
buffer, and make possible some simple self-modifying code (such as 
changing the second byte of an INT instruction)

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