Paired 68000 systems - was Re: out-of-mainstream minis

Johnny Billquist bqt at
Sat Jul 4 06:39:08 CDT 2015

On 2015-07-04 04:11, Toby Thain wrote:
> On 2015-07-03 8:09 PM, Glen Slick wrote:
>> On Jul 3, 2015 4:59 PM, "Johnny Billquist" <bqt at> wrote:
>>> I find it hard to believe it was a plain 68K in there. That CPU have
>>> some
>> serious issues that makes it close to impossible to implement virtual
>> memory or proper usermode protection.
>>> (Yes, it can be done, but the amount of hardware required means most did
>> not. I think SUN did it with their own MMU, and an extra CPU in there.
>> Trying to remember who else - I seem to remember one other company who
>> actually used a plain 68K, and it was not Unisys.)
>> Apollo is the classic example of using plain 68K (two).
> I always associate it with Tandem:

Tandem have definitely done lots of funky stuff. The dual 68K designs 
mentioned in that paper, though, is for lock stepped 68K in peripherial 
controllers, to detect hardware errors. Thus, they are not running 
something close to a "normal" operating system. In that environment 
there are no problems with the 68K at all. The dual processor design in 
Tandem is purely for the fault tolerance parts.


Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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