[Info-vax] OT: obscure PDP11 OSes (even more dinosaury)

[BillPedersen]

On Saturday, June 20, 2015 at 4:29:32 PM UTC-4, Hans Vlems wrote:
> My question was whether the 11/20 had support for 18 bit addresses. I thought that the 11/20 was the only model limited to a 2^16 address space.

I am not aware of an option being made available publicly for the low end PDP-11s to have more than 28K of memory.  It should be noted that actually you could run up to 30K of physical memory if my memory serves me right, but you needed to be very careful on the use of hardware device register addresses.

We had a -11/20 in one of our labs in the department.  Never had anything on it but DOS-11.

The Unibus had been designed with expansion in mind.  But the expansion and also subsequent success came with the -11/45 and then later the 11/34 and other machines of that era.

Since these machines were faster than also had the 18-bit memory management the need to introduce an option for the low end systems sort of evaporated.

Bill.