philip@cel.cummins.com (Philip D. Pokorny) (06/10/91)
Dave Funk writes: > Given that there is some question about the correctness of that info, > I asked our salesrep to check up on it. He sent a query into the Sales > Response Center and got the reply that ECC memory is used in all > series 400 and 700 systems. > > Thus it looks like I jumped the gun on this one. > Sorry about that folks ;{ I also talked with my sales rep again and he found a mention someplace that the 425e does use SIMM memory... It also says ECC in the same breath... The prices for an 8 Mb upgrade to a 425t and 425e show a $500 difference... (But this may be because one uses 4Mb chips and the other 1Mb) In retrospect, it may be that the 425e uses memory designed in the "image" of PC SIMM memory while not actually being compatible with PC SIMM memory... SIMM stands for something like Single In-line Memory Module. It describes a way of makeing memory modules that place surface- mounted ships on a PC board and use the edge of the PC-board as the connector. This saves the cost of a connector (something you will find on 425t memory) as well as making the modules much easier to manufacture. (Connectors must frequently be placed on the PC board by hand.) The boards are rectangular making it easy to pack many individual boards into a single production run, as well as making them easy to separate However, the fact that the 400 uses ECC and not Parity to check it's memory, would imply that the two memory boards will not be interchangeable. Different computers have different memory protection schemes. Some Macintosh computers use SIMM memory but the Mac has no memory protection logic and thus uses 8 bit wide SIMM's. The PC uses a parity bit for each byte of memory and thus uses SIMMS that are 9 bits wide (8 data + 1 parity). These new 425e's will probably use something different. I was told by an Apollo hardware engineer that when your memory bus it 32 bits wide, it's easy to add ECC because it only takes 5 or 6 bits to do ECC and you've already got 4 if your using parity. (That's why HP is going with ECC on all it's new products.) We can only hope that the 425e memory will be cheaper than the 425t memory since it should be easier to manufacture. I would however like to suggest that the ECC/Parity tradeoff be something that the user could select. Perhaps they could develop a 10-bit wide SIMM that is socket COMPATIBLE with a 9-bit wide SIMM. That would allow ECC to be done with a mixture of 10 and 9 bit wide SIMM's, and parity with all 9-bit wide. This would be cheaper for HP as well because they could PURCHASE the memory on the PC open market as needed, and not have to worry about uncertain market projections on memory purchases. Due to the volume of 9-bit SIMMS sold, the costs should be lower for everyone... At the risk of bashing HP, I would like to close by noting that too many companies seem to want to see their name on everything they sell. (Ever noticed at McDonalds that EVERYTHING has the golden arches on it (Ketchup, milk, orange juice, straws...) In the short run this may seem like a good idea, but I think in the long run it leads to higher costs because each one of those is a purchased item that must be special ordered and specially manufactured. (No change-over is still quicker and cheaper than quick change-over). This ruins the savings associated with volume production and single part number inventory. Sincerely, Philip D. Pokorny philip@cel.cummins.com :)