On 2015-08-19 20:11, Miod Vallat wrote:
I don't have any hardware information, but an educated guess would be that you need some additional address lines routed from the CPU to the memory sockets. The CPU itself have the necessary address lines on pins, but unless they also go to the memory sockets, you cannot get that high in memory. But from a CPU point of view, there is nothing speical about going to 512 Megs. Or even more. But if you go for more physical memory, you need an NVAX (which I think the 4000 machines have), and the OS needs to change the mode of the CPU, which I suspect VMS will not do on a 4000 machine, as they would not expect you to have that amount of physical memory that would require changing from the default mode.I'm afraid the large physmem mode allowing more than 512MB of physmem is only available on NVAX+ cpus (those pin-compatible with 21066), not NVAX.
Well, unless my memory fails me (which happens) the limit on the old VAX memory model is 1G, not 512M. However, on all machines that I know of, this 1G space was split in two, with 512M reserved for physical memory, and 512M reserved for I/O stuff.
It got extended to 34 bits, but I was pretty sure it was in the NVAX already. But I might be wrong. And I'm not sure the processor is pin-compatible with the Alpha. However, the VAX-7000 uses the same bus as the DEC 7000, and a change from one to the other only required replacing the CPU card. The rest remained. And I seem to remember that the VAX 7000-600 used a plain NVAX, the 7000-700 the NVAX+, and the 7000-800 the NVAX++.
Johnny