Reliability of Computer Memory?

olddoc writes "In the days of 512MB systems, I remember reading about cosmic rays causing memory errors and how errors become more frequent with more RAM. Now, home PCs are stuffed with 6GB or 8GB and no one uses ECC memory in them. Recently I had consistent BSODs with Vista64 on a PC with 4GB; I tried memtest86 and it always failed within hours. Yet when I ran 64-bit Ubuntu at 100% load and using all memory, it ran fine for days. I have two questions: 1) Do people trust a memtest86 error to mean a bad memory module or motherboard or CPU? 2) When I check my email on my desktop 16GB PC next year, should I be running ECC memory?"

Comments

Answers

[jawtheshark]

1) Yes

2) No

Now to be serious. Home PC do not come yet with 6GB or 8GB. Most new home PC still seem to have between 1GB and 4GB. Where the 4GB variety is rare because of the fact that most home PCs still come with a 32-bit operating system. 3GB seems to be the sweet spot for higher-end-home-pcs. Your home PC will most likely not have 16GB next year. Your workstation at work, perhaps, but then even perhaps.

At the risk of sounding like "640KByte is enough for everyone", I have to ask why you think why you need 16GB to check your email next year. I'm typing this on a 6 year old computer, I'm running quite a few applications at the same time and I know a second user is logged in. Current memory usage: 764Meg RAM. As a general rule, I know that Windows XP runs fine on 512Meg RAM and is comfortable with 1GB RAM. The same is true for GNU/Linux running Gnome.

Now, at work with Eclipse loaded, a couple of application servers, a database and a few VMs... Yeah, there indeed you get memory starved quickly. You have to keep in mind that such usage pattern is not that of a typical office worker. I can imagine that a heavy Photoshop user would want every bit of RAM he can get too. The Word-wielding-office-worker? I don't think so.

Now, I can't speak for Vista. I heard it runs well on 2GB systems, but I can't say. I got a new work laptop last week and booted briefly in Vista. It felt extremely sluggish and my machine does have 4Gig RAM. Anyway, I didn't bother and put Debian Lenny/amd64 on it and didn't look back.

I my idea, you have quite a twisted sense of reality regarding to the computers people actually use.

Oh, and frankly... If cosmic rays would be a big issue by now with huge memories, don't you think that more people would be complaining? I can't say why Ubuntu/amd64 ran fine on your machine. Perhaps GNU/Linux has built-in error correction and marks bad RAM as "bad".

Re:Memtest not perfect.

[Anonymous Coward]

Another nice tool is prime95. I've used it when doing memory overclocking and it seemed to find the threshold fairly quickly. Of course your comment still stands - even if a software tool says the memory is good, it might not necessarily be true.

RAID(?) for RAM

[Xyde]

With memory becoming so plentiful these days (I haven't seen many home PC's with 6 or 8GB granted, but we're getting there) it seems that a single error on a large capacity chip is getting more and more trivial. Isn't it a waste to throw away a whole DIMM? Why isn't it possible to "remap" this known-bad address, or allocate some amount of RAM for parity the way software like PAR2 works? Hard drive manufacturers already remap bad blocks on new drives. Also it seems to me that, being a solid state device, small failures in RAM aren't necessarily indicative of a failing component like bad sectors on a hard drive are. Am I missing something really obvious here or is it really just easier/cheaper to throw it away?

Depends

[gweihir]

My experience with a server that recorded about 15TB of data is something like 6 bit-errors per year that could not be traced to any source. This was a server with ECC RAM, so the problem likely occured in busses, network cards, and the like, not in RAM.

For non-ECC memory, I would strongly syggest running memtest86+ at least a day before using the system and if it gives you errors, replace the memory. I had one very persistend bit-error in a PC in a cluster, that actually reqired 2 days of memtest86+ to show up once, but did occure about once per hour for some computations. I also had one other bit-error that memtest86+ did not find, but the Linux commandline memory tester found after about 12 hours.

The problem here is that different testing/usage patterns result in different occurence probability for weak bits, i.e. bits that only sometimes fail. Any failure in memtest86+ or any other RAM tester indicates a serious problem. The absence of errors in a RAM test does not indicate the memory is necessarily fine.

That said, I do not believe memory errors have become more common on a per computer basis. RAM has become larger, but also more reliable. Of course, people participating in the stupidity called "overclocking" will see a lot more memory errors and other errors as well. But a well-designed system with quality hardware and a thourough initial test should typically not have memory issues.

However there is "quality" hardware, that gets it wrong. My ASUS board sets the timing for 2 and 4 memory modules to the values for 1 module. This resulted in stable 1 and 2 module operation, but got flaky for 4 modules. Finally I moved to ECC memory before I figuerd out that I had to manually set the correct timings. (No BIOS upgrade available that fixed this...) This board has a "professional" in its name, but apparently, "professional" does not include use of generic (Kingston, no less) memory modules. Other people have memory issues with this board as well that they could not fix this way, seems that somethimes a design just is bad or even reputed manufacturers do not spend a lot of effort to fix issues in some cases.In can only advise you to do a thourough forum-search before buying a specific mainboard.

 

Re:The truth

[Mr Z]

Note: having more memory increases your error rate assuming a constant rate of error (per megabyte) in the memory. However, if the error rate drops as technology advances, adding more memory does not necessarily result in a higher system error rate. And based on what I've seen, this most definitely seems to be the case.

Actually, error rates per bit are increasing, because bits are getting smaller and fewer electrons are holding the value for your bit. An alpha particle whizzing through your RAM will take out several bits if it hits the memory array at the right angle. Previously, the bits were so large that there was a good chance the bit wouldn't flip. Now they're small enough that multiple bits might flip.

This is why I run my systems with ECC memory and background scrubbing enabled. Scrubbing is where the system actively picks up lines and proactively fixes bit-flips as a background activity. I've actually had a bitflip translate into persistent corruption on the hard drive. I don't want that again.

FWIW, I work in the embedded space architecting chips with large amounts of on-chip RAM. These chips go into various infrastructure pieces, such as cell phone towers. These days we can't sell such a part without ECC, and customers are always wanting more. We actually characterize our chip's RAM's bit-flip behavior by actively trying to cause bit-flips in a radiation-filled environment. Serious business.

Now, other errors that parity/ECC used to catch, such as signal integrity issues from mismatched components or devices pushed beyond their margins... Yeah, I can see improved technology helping that.

Re:Memtest not perfect.

[Idaho]

My experience with memtest is you can trust the results if it says the memory is bad, however if the memory passed it could still be bad.

I wonder how strongly RAM stability depends on power fluctuations. While you're testing memory using Memtest, the GPU is not used at all, for example. When playing a game and/or running some heavy compile-jobs, on the other hand, overall power usage will be much higher. I wonder if this may reflect on RAM stability, especially if the power supply is not really up to par?

If so, you might never find out about such a problem by using (only) memtest.