[HECnet] Simplest PDP-11

[Göran Åhling]

With J11, the 11/93 (system board) was designed with no memory cache, 
but full memory size (4 MByte) fast enough to run full processor speed, 
thus making cache techniques non profitable. Maybe not an issue for the 
CPU design itself, but quite central for the system design.

Previous (11/73, 11/83, possibly also 11/53) used cache, thus are they 
more complicated compared to 11/93.

Memory mapping is there in all of them, naturally, as 16 address-bits in 
the CPU must cope with 22 (or 18) bits of memory addressing, but I doubt 
that any "modern version" of the asked systems will run in a PDP with 
only 32 kWord/64 kByte memory.

/Göran

Den 2019-02-04 kl. 00:56, skrev Johnny Billquist:
> On 2019-02-04 00:14, Brian Hechinger wrote:
>> What about the different CPUs?
>
> You can essentially group them in to a few different groups.
>
> But for anything able to run RSX-11M-PLUS, RSTS/E and BSD, we're 
> essentially talking about the 11/70 class, which includes the 11/44, 
> 11/70 and all J11 based machines. They are pretty similar, but I guess 
> the J11 is the slightly simpler one of them, if you really want to get 
> down to it.
>
> Oh, and any Qbus machine is easier than Unibus ones.
>
>   Johnny
>
>>
>> On Sun, Feb 3, 2019, 17:11 Johnny Billquist <bqt at softjar.se 
>> <mailto:bqt at softjar.se> wrote:
>>
>>     On 2019-02-03 22:42, Brian Hechinger wrote:
>>      > On Sun, Feb 3, 2019, 16:15 Johnny Billquist <bqt at softjar.se
>>     <mailto:bqt at softjar.se>
>>      > <mailto:bqt at softjar.se <mailto:bqt at softjar.se>> wrote:
>>      >
>>      >     On 2019-02-03 22:02, Brian Hechinger wrote:
>>      >      > What is the simplest PDP-11 CPU/peripheral design that is
>>     capable of
>>      >      > running RSX-11, RSTS/E or BSD?
>>      >
>>      >     Define "simple" please. :-)
>>      >
>>      >
>>      > The easiest to implement with limited tools.
>>
>>     If the size of the device driver is anything to go on, then roughly
>>     ranked from easiest:
>>     RK11
>>     TC11
>>     RP11
>>     RL11
>>
>>     Massbus in general I think can be done to work without too much
>>     complexity. RK611 shouldn't be too bad, but do add a bit more stuff.
>>
>>     But I think pretty much anything except MSCP is roughly similar in
>>     complexity for someone implementing it.
>>
>>         Johnny
>>
>>      >
>>      >      > Also, what is the minimum disk space needed to install 
>> those
>>      >     operating
>>      >      > systems? I have a plan. Probably not a good one but I'll
>>     likely
>>      >     learn a
>>      >      > lot in the the process so it won't be a waste of time.
>>      >
>>      >     RSX-11M-PLUS can run from two RL02, if you just accept the 
>> pregen
>>      >     system. But that's the smallest. If you want to build stuff,
>>     something
>>      >     like an RK07 is required, and that is 28 Megs. But I think 
>> it's
>>      >     recommended that you have two. But that probably is for more
>>     reasons
>>      >     than just running the actual system (it is hard to do an
>>     update if you
>>      >     are running on an RK07, and the update media is an RK07).
>>      >
>>      >     RSX-11M definitely gets away with less. RSTS/E would be
>>     similar, I
>>      >     think, while BSD probably wants a little more.
>>      >
>>      >
>>      > Ok, that's what I needed to know (more ballpark than anything
>>     else is fine)
>>      >
>>      > Thanks!!
>>      >
>>      > -brian
>>
>>
>>     --     Johnny Billquist                  || "I'm on a bus
>>                                         ||  on a psychedelic trip
>>     email: bqt at softjar.se <mailto:bqt at softjar.se>    ||     Reading 
>> murder books
>>     pdp is alive!                     ||  tryin' to stay hip" - B. Idol
>>
>
>

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