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Ask the Wizard Questions

Optimizing memory on a 3300AXP

The Question is:

Dear Wizards,

How can I optimise memory usage on my 3300AXP ? I have 64 M installed on this machine which is used as a personal workstation to support in-house applications on a variety of machines , including other VMS boxes.

I run DECnet , TCP/IP , X.25 in the background, along with a few print queues. DECterms are used to access remote hosts, typically 4-8 terminals.

I know that AXP technology uses a lot more memory , but I suspect that I can make better use of what I have.

Even with 64M installed , I can still have several processes swapped out.

What really kills it is when I want to run Softwindows
( We really wanted to have dual boot VMS/WNT machines but the 150 was not released when we bought the 3300s)

Many Thanks,

The Answer is:

Swapped out processes is not a bad thing. They had to have been fairly idle to get swapped out in the first place. If they do anything they'll be swapped back in. The real trouble comes when processes thrash, swapping in and out, again and again. You might be able to determine just how much swapping in and out is going on by using the monitor utility. I think the MONITOR STATES /ALL function would be most useful.

Typically, long before swapping becomes a big problem, the system will be paging, especially hard faulting, a lot. Be on the look out for this.

I have a DEC 3000 model 500. Originally, I had 128MB and experienced only a little outswapping. Now I have 320MB and have boosted the virtual cache. 64MB does seem a little small, perhaps an upgrade would be in order?

Do you make use of AUTOGEN regularly? It will help optimize memory usage.

Alpha uses more memory for instructions for two reasons; 1) it takes more RISC instructions to get the job done as compared to VAX; 2) the modern compilers are more aggressive at unrolling loops. In my experience a factor of x2 or x3 is to be expected. Alpha also tends to use more memory for data. The primary cause of this is bigger/more buffers to minimize I/O. Secondarily, data is aligned to natural boundaries. There is another effect Alpha has on virtual memory. This is due to the relatively large page size. At 8KB (and 64KB for staticly linked image sections) considerably more virtual memory may be idle. This does have an effect on physical memory which depends heavily upon application details. Lots of 1 byte global sections didn't hurt so bad on VAX, only wasting 511 bytes per section. The same approach on Alpha wastes 8191 bytes physical and as much as 65,535 bytes virtual on current models. Thankfully noone (that I know of) ever uses 1 byte sections.

DEC SoftWindows/SoftPC for OpenVMS AXP - Version 5.0 uses software to emulate the Intel x86 instruction set. This is fine for the occasional use but prohibitive for anything more. If what you want to do it run Intel binaries all day long get an Intel-based system. Digital has many excellent examples available. If what you want is run both Intel and Alpha images all day long then consider client/server. Perhaps eXcursions would be useful.