[HECnet] SIMH VAX memory weirdness

[Johnny Billquist]

Well, I didn't write 7.3-1, I asked if it really was correct that Sampsa was using it, as I believe 7.3 was the last release for VAX. :-)

And I said "in theory", since I'm not sure any existing VAX ever brought out all 34 address bits, but there are really 34 physical address bits in the VAX extended addressing mode. Check the spec.
The address field in a PTE can be either 21 bits (traditional) or 25 bits (extended). Add to that, the address within the page (9 bits), and you'll end up with either 30 bits, or 34 bits of physical addresses.

32 bit physical addresses have never existed on a VAX.

	Johnny

On 2010-11-29 07:07, hvlems at zonnet.nl wrote:
Umm Johnny it must have been late when you wrote this..
The last release for VAX was 7.3. Anything later is alpha or ia64. 7.3-1 was only released for alpha.
The address space for VAX is 32 bits, no page bits. And 2**32 is 4G. Where did you find 16 GB?

------Origineel bericht------
Van:Johnny Billquist
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Onderwerp: Re: [HECnet] SIMH VAX memory weirdness
Verzonden: 29 november 2010 02:03

On 2010-11-28 21:20, Sampsa Laine wrote:
I just increased the memory on one of my SIMH VAX VM's to 512 MB from 64 MB - the system boots fine but SHOW MEMORY (under OpenVMS 7.3-1) still reports 64 MB.

Do I need to tell the VMS installation about the new RAM somehow? How much RAM does 7.3-1 (VAX) support anyway?

7.3-1 ??? I thought the last version of VMS for VAXen was 7.3

As for memory, VMS (on VAX) supports up to (in theory atleast) 16G of
physical memory. However, that requires the extended memory mode PTEs,
which only came with NVAX, so no luck with simh.

The "older" layout supports a max of 1G, but I think all architectures
machines split that into 512M of RAM and 512M for I/O space.

Oh, and when you add memory, you need to run an AUTOGEN afterwards, to
change a bunch of parameters to the new hardware config (whould be
obvious ;-) ).

	Johnny



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