Happy Birthday VAX 11/780 (influence of)

Fred Cisin cisin at xenosoft.com
Wed Oct 27 16:20:52 CDT 2010

> > I do believe the PDP-11's use of memory-mapped I/O was original - at least I
> > can't think of any earlier examples.  -- Ian

On Wed, 27 Oct 2010, Ethan Dicks wrote:
> It's the earliest one I am aware of, but my knowledge of non-DEC stuff
> before 1970 is admittedly full of gaps.
> I started with the 6502 (in 1977), so I thought memory-mapped I/O was
> "normal".  The 1802 was the first processor I used that had I/O
> instructions.
> So I guess since any processor that has gaps in its memory map _could_
> have those gaps filled with memory-mapped I/O, the question is _did_
> any implement it prior to 1969/1970?

My memories from ~1968 are not very clear, and definitions of
memory-mapped I/O may vary, . . .
Didn't the 1401 sort-of have it?   Not fully automatic memory-mapped I/O
such as the TRS80 and PC video RAM, more like the CP/M and PC's PSP DTAs.
I seem to recall there being a command to read a card into a fixed buffer
in memory, and another to write a card from anbother fixed buffer.  I
remember "cheating" and using those buffer spaces when I ran short of
space writing short programs on the 1401 emulator on the 1620.

Strange, . . .
I remember more about that than I do about PDQ FORTRAN on the 1620, nor
about "141 SPS"? on the 1401.

Grumpy Ol' Fred     		cisin at xenosoft.com

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