dfriedlander@cdp.UUCP (06/29/89)
It's true, diagnostics don't seem to pick up all memory problems. My AST386C ran fine under DOS (5MB memory.) Indeed, not only did diagnostics show no problem, but I was able to fill up all the memory using Lotus and EMM, and nothing showed. (Incidentally, the Lotus and EMS test is generally better than the provided diagnostics programs). Nonetheless, UNIX hung the system periodically. When the memory was swapped for AST memory, the problem went away. I wonder if anyone understands why this sort of weirdness happens. David Friedlander Io Consulting Inc.
steveb@cs.utexas.edu (Steve Benz) (06/30/89)
In article <143800004@cdp> dfriedlander@cdp.UUCP writes: > [ NMI in System Mode == memory problem ] >It's true, diagnostics don't seem to pick up all memory problems. ... > >I wonder if anyone understands why this sort of weirdness happens. I have some experience with this one on the 286, it seems that some memory expansion cards -- particularly those which haven't got dip-switches or circuitry to determine the upper-bound of memory -- don't work, and display exactly the symptoms that have been described. My theory as to why this problem occurs in Unix, but not in DOS or in the diagnostics is that those two never try and do DMA to the upper reaches of memory. - Steve
marc@noe.UUCP (Marc de Groot) (07/03/89)
In article <143800004@cdp> dfriedlander@cdp.UUCP writes: >It's true, diagnostics don't seem to pick up all memory problems. >My AST386C ran fine under DOS (5MB memory.) Indeed, not only did >diagnostics show no problem, but I was able to fill up all the memory > [ ... ] >I wonder if anyone understands why this sort of weirdness happens. Memory tests which REALLY test memory are not as easy to write as they might appear. There are quite a variety of problems which cause memory to fail. Any memory error where a bit a just STUCK was detected when your machine was burned in. In other words, the manufacturer got all the EASY problems. Your memory probably works 99.9% of the time -- it's a very occasional bad write of a bit that is causing the failure. The memory test that the PC does at power-on is hopelessly ineffective at catching marginal memory errors simply because it does not test the memory long enough, and because it does not vary the patterns that it writes. Back in prehistoric times, when I had a S-100 bus machine with a Z80, we had the "Rasmussen memory test" which had a good-sized repertoire of different memory tests that it would run. I would leave it running for HOURS to catch marginal memory. I haven't seen anything like this for PC's. -- Marc de Groot (KG6KF) These ARE my employer's opinions! Noe Systems, San Francisco UUCP: uunet!hoptoad!noe!marc Internet: mdg@postgres.berkeley.edu -or- marc@kg6kf.AMPR.ORG