Found the source of my unstable system

Recently I upgraded to 3GB while on Vista. Instant blue screen.
So then I install XP and it's ok for awhile. Then InstallShield keeps telling me CABs are corrupt on CD's I've only used once. So I alter the memory timings and everything seems to be ok. Recently I started having applications throw exceptions that have never thrown before. Finally I broke down and burned an ISO of Windows Memory Diagnostic.

Tested the full 3GB and every test failed.
Tested each stick independently and 1 in particular always failed.

The third stick would do this:

Expected: fe-fe-fe-fe::fe-fe-fe-fe
Actual: fe-fe-fe-fe::fe-fe-ee-fe

Every time on every test the third byte in the high order word was wrong. So if you had a pointer that relied on some object at an address the pointer would be wrong and of course would throw an exception.

Problem solved.

In short when you buy memory...test it. Woulda saved me a lot of headaches.

RAM from my experience has a fairly high failure rate... over the years I've bought 20 or so sticks of RAM and have had to replace, I think, four of them for one reason or another. I'm talking very reliable brands, as well... you just have to get used to the fact that they have such a high failure rate.

I have never had new RAM fail until just recently! I agree it can be a real pain in the rear. Thorough testing is a must! I always use MemTest and Orthos to verify my RAM.

Lately, it seems like getting good RAM is just pure chance. I'll tell a friend how easy it is to upgrade their RAM by directing them to a online memory configurator and if the don't get the wrong RAM then they get faulty RAM! So much for easy.

Still... quiet annoying the fact RAM is being sold that a simple diagnostic can show to be faulty.

Yes, very. From my experience with quality control I'd say they test a sample size of each production run. This means that not every module would be tested so I'm sure some bad ones get through.

Which brand did you buy?

> This means that not every module would be tested so I'm sure some bad ones get through.
Not to mention it *could* get damaged in transport. After the diagnostic perhaps?

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Originally Posted by zacs7

> This means that not every module would be tested so I'm sure some bad ones get through.
Not to mention it *could* get damaged in transport. After the diagnostic perhaps?

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Somehow, I don't see that as the true cause. I mean, RAM has no moving parts and the rate of error is way too high. I almost doubt that many drives would get messed up in the transport.

What diagnostic? Things such as RAM is not tested before it's shipped since it would take way too much time.

I'd say it's almost completely luck of the draw, although fate seems to smile on me as far as memory goes, never had a failure yet (although admittedly I only buy new memory for new equipment, that's every 4 years on average).

Same with hard disk drives. My stuff works fine, then I pass it on and I hear a few months down the line that it's seized up. :rolleyes:

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What diagnostic? Things such as RAM is not tested before it's shipped since it would take way too much time

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I've never been in any production environment that did not test a small sample size from each production run. I've been involved with machines, glass, engines, parts, etc. Everything that is made has some type of QA analysis setup so that the factory can monitor quality. You can't just produce, forget, and ship. It doesn't work like that.

Samples, sure. But that's just a small subset of all the production.
That's why warranty exists, just in case something should break.

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Originally Posted by Elysia

Samples, sure. But that's just a small subset of all the production

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These "samples" are used to calibrate the production line. Under high quality control requirements, once calibrated a production line produces basically the exact same product (there's a well known failure rate).

What it seems is that, quality requirements have been lowered or production lines are not being adequately calibrated or whatever.

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What it seems is that, quality requirements have been lowered or production lines are not being adequately calibrated or whatever.

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Hehe. Sounds like a fellow QA guy. Rememeber it's always an auditor's fault but never the line's.

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Originally Posted by Mario F.

What it seems is that, quality requirements have been lowered or production lines are not being adequately calibrated or whatever.

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I'm thinking you might be right.

One of the problems with memories and their compatibility with various systems is that when they are run at high speed - such as 400MHz DDR or 800MHz DDR2 - the margins are wafer-thin. And variance isn't just in the memory sticks, but also in the connector, the motherboard, the memory controller and the processor itsef. If you have a particularly slow pad on one pin on the memory controller, the memory can be will within margins, but still won't work on the system.

I had a memory problem with a Xen virtual machine - the memtest86 that comes with most Linux distro's would run just fine running alone [that is when booing directly into memtest86], but when running a virtual machine in Xen, it would fail to read that memory - just one bit was wrong, and I even wrote my own little version of the particular test in memtest86. Changing the memory to another two sticks of the same brand fixed the problem. Obviously, running with virtualization enabled changed some timing in accessing the memory - perhaps it did some page-table fetching that didn't happen during the normal run, for example.

And yes, it can be difficult to find memory errors, because other interference can cause problems to come and go.

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Mats

That did, of course, remind me that motherboards are very complex piece of hardware and are, in fact, still created by hand and not a manufacturing process!
So it may very well be the motherboard at fault and not the memory, or a combination of the two.

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Originally Posted by Elysia

That did, of course, remind me that motherboards are very complex piece of hardware and are, in fact, still created by hand and not a manufacturing process!

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Huh? The motherboards are designed by humans, but the manufacturing and assembly of millions of boards is not done by human hands to any large extent. Ok, some through-hole mounted connectors [such as the power connector] may be hand-soldered, but certainly the memory sockets and all the main components are machine placed (mounted) and wave-soldered, like any other mass-produced electronics.

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So it may very well be the motherboard at fault and not the memory, or a combination of the two.

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I've seen a fair share of "doesn't work well together" where one processor, or one stick of memory will work fine in one model of motherboard, and move to another model of motherboard and the same component, it will fail. But swap to another similar part on that motherboard, and it works just fine. That's what's called "marginal issues", where the timing parameters of one component are straddling the parameters of the other component - and too fast is just as bad as too slow in this case.

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Mats

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Originally Posted by matsp

Huh? The motherboards are designed by humans, but the manufacturing and assembly of millions of boards is not done by human hands to any large extent. Ok, some through-hole mounted connectors [such as the power connector] may be hand-soldered, but certainly the memory sockets and all the main components are machine placed (mounted) and wave-soldered, like any other mass-produced electronics.

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Sure, the individual pieces are all manufactured, but everything is typically (or at least some) put together by human hands due to the complexity. I saw this process once on a demonstration movie.
Anyway, it just makes it possible for even higher margins of errors.

Complex stuff...

Just out of curiosity, would you say quality control is being relaxed and warranties increased?

Recently I found first hand that a few hundred thousand BenQ monitors had failed 'quality control' -- dry solder (the solder machine completely missed). Luckily I got my monitors fixed before the warranty expired ;). Is that quality control's responsibility?

Also, hypothetically, could a crate of RAM not be stacked next to some crate of 'damaging material'?

Well, a dry solder joint may not be detected until the equipment starts coming back after it's failed [because the solder is holding up enough to not fail during factory tests]. Sure, someone should visually inspect the joints from time to time, and it's certainly a "QC failure" if something makes it out of the factory with faults like that - but it's also understandable that you expect machines to do what they are supposed to for most of the time.

In all industries, there is a balance between how much effort you put on checking the product before it gets to the customer, vs. having to replace shipped product. The ideal balance is such that you "don't upset too many customers, don't loose too much money on replacements", but also "don't spend TOO much on QA". Some companies haven't found the right balance all the time - I remember Seagate having problems with their hard-disks some 15-20 years back - not sure about them now, if they still exist...

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Mats

They do and they recently purchased Maxtor.