In March, 2000, many of us received a mailing from a memory vendor, who shall remain nameless, that talked about greater memory requirements for MPE/iX 6.5 and made statements such as:

"The most important of these features [of MPE/iX 6.5] is the abolishment of the 3.75 GB memory addressing performance limitation....Customers upgrading to 6.5 will experience enormous performance improvements as they configure memory up to the new physical maximums....Customers can expect to more than double overall speed and throughput under these new supportable memory configurations with no corresponding software upgrade charges."

And, finally, the kicker that got people talking on HP3000-L: "Minimum memory requirement for MPE 6.5 is 4 GB."

This last was included on a page with a handy dandy "HP Memory Calculation Formula" you could use to determine how much more memory you needed to purchase, presumably from this vendor. According to this formula, my 959/400 production box that happily supports 650 concurrent users on MPE/iX 5.5 PP7 with 2 GB of memory should have 8.2 GB of memory for MPE/iX 6.5! I don't think so.

Anyway, note this is also the vendor with the slightly sleasy offer of "upgrade to one of our promotional memory configurations... and we'll send you to HPWorld 2000 all expenses paid."

The "how much memory will I really need" thread was started by some poor system manager trying to respond to his manager's questions about this memory vendor's mailing:

"My manager recieved one of those HP memory calculation formula sheets from .... He plugged in the numbers and it told him we needed to add at least 4 GB of memory to our 939KS. They even have a line that says the minimum memory requirement for 6.5 is 4 GB. If anyone else has seen this mailing, how does it compare to your actual memory configuration? I would like some real world comparisons to use in my response."

From Jerry Fochtman: "This is an incorrect statement, as we've loaded 6.5 on test systems with significantly less memory than 4 GB and they ran just fine."

From Steve Cole: "I've never been one for using a formula for calculating memory. The amount of memory that is optimal for a given system is dependent on a lot of different things that affect the memory loading. On the other side it's rare to find a HP3000 that doesn't benefit when more memory is added."

From Dennis Heidner: "There are all kinds of caveats with memory including application mix, memory interleaving, mixing 512MB modules, 256MB modules, carriers, etc. I prefer to use the rule of thumb that new machines start with 1 GB if possible and, if the budget permits, max out the memory. Almost every version of the OS takes additional memory (but not as much as the suggested increment).

From Mike Hornsby: "Any memory requirements formula would have to be based on: applications type/mix, processor speeds, and number of active processes. In my opinion the formula from the memory vendor doesn't seem to take any of these into consideration...I have seen many cases were additional memory will speed up read only batch processes to the detriment of interactive response times. So one has to question claims like %50 faster and ask for more specifics based on the type of performance problem at hand...A primary concern in adding memory to a multi processor system is the memory interleave configuration. In my opinion, the amount of memory added is a secondary to the number of interleaves created."

I'll give the final word to Bill Lancaster: "The 1GB per processor is dead wrong. The "right" answer for how much memory you should buy is "How much can you afford?". There is currently almost no point of diminishing returns on memory (except for some very unusual edge cases), although this may change with MPE/iX 6.5 as more memory becomes configurable (up to 16 GB). Many times people have used convoluted rules-of-thumb to answer this question. Largely, these are a waste of time, especially since memory is so cheap. (Isn't competition a wonderful thing?) Additional memory often helps online transaction performance but very often dramatically improves read-oriented serial batch performance. Bottom line is buy as much as you can afford and don't spend a lot of time trying to justify it, if you can help it."

OK, I lied, since I am going to have the final word after all. Unfortunately, no one from HP chimed in on this thread with an answer on MPE/iX 6.5 memory requirements. But I think there is a good reason for this: no one really knows yet. There is very little "real world" experience with MPE/iX 6.5 to make a judgement on memory requirements. Because of all the variables involved, I doubt we will ever have a one-size-fits-all formula for optimum memory size. Bill's "buy as much as you can afford" guideline, to which I'll add "don't try to save money by skimping on memory" will likely remain the best advice.

Oh, and about that supposed 4 GB minimum memory requirement for MPE/iX 6.5? Only those HP e3000 servers that use the PA8000 or PA8200 processor chips (the PA-RISC 64 bit chips) will be able to use memory sizes greater than 3.75 GBs. This includes certain of the 9x9KS servers (the 929KS/030, 939KS/030, 979KS, 989KS/x00 and 989KS/x50 Servers) and the 997 servers. The PA7xxx processor based servers will not be able to support memory sizes greater than 3.75 GBs. These include the 9x7, 9x8, 939KS, 929KS/020, 939KS/020, 959KS, 969KS/x00, 969KS/x20, 992/990, 995/991 and 996 servers.