Slashdot Mirror
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?"
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. Troubleshooting your scenario should involve replacing the DIMM's in questions with known good modules while running Windows.
brandelf -t FreeBSD
First, it was not cosmic rays; memory was tested in a lead vault and showed the same error rate. Turns out to have been alpha particles emitted by the epoxy / ceramic that the memory chips were encapsulated in.
That said: Quite clearly given your experience, Vista and Ubuntu load the memory subsystem quite differently. It is possible that Vista, with its all-over-the-map program flow, is missing cache a lot more often and so is hitting DRAM harder; I don't have the background to really know. I believe that Memtest86, in order to put the most strain on memory and thus test it in the most pessimal conditions, tries to access memory in patterns that equally hit physical memory hardest. But, what I have found is that some OSs, apparently including Ubuntu, will run on memory that is marginal, memory that Memtest86 picks up as bad.
As for ECC in memory... The problem is that ECC carries a heavy performance hit on write. If you only want to write 1 byte, you still have to read in the whole QWord, change the byte, and write it back to get the ECC to recalculate correctly. It is because of that performance hit that ECC was deprecated. The problem goes away to a large extent if your cache is write-back rather than write-through; though there will be still a significant number of cases where you have to write a set of bytes that has not yet been read into cache and does not comprise a whole ECC word.
That said, it is still used on servers...
But I don't expect it will reappear on desktops any time soon. Apparently they have managed to control the alpha radiation to a great extent, and so the actual radiation-caused errors are now occurring at a much lower rate, significantly lower than software-induced BSODs.
Not all memory is created equal. Memory can be bad if Memtest detects errors, or you can simply be running it at the wrong settings. Usually there are both "normal" and "performance" settings for memory on higher end motherboards, or sometimes you can tweak all sorts of cycle-level stuff manually (CAS latency etc.).
Try running your memory with the most conservative settings before you assume it's bad.
.: Max Romantschuk
Yes. Vista is rock solid on solid hardware. Seriously. Vista is as reliable as Linux. Some people wreck their vista installation, some people wreck their Linux installation.
This is your sig. There are thousands more, but this one is yours.
Agreed. People who will sit and tell me with a straight face that Vista, in their experience, is unstable are either very unlucky, or liars. Windows stopped being generally unstable years ago. Get with the times.
"16MB (fuck off, MiB fascists)" - The Mighty Buzzard
Just FYI, 32bit Intel processors from the Pentium Pro generation and forward (with the exception of most, if not all of the Pentium-M's) have 36 physical address pins or more?
Many, but not all, chipsets have a facility for breaking the physical address presentation of the system RAM into a configurably-sized contiguous block below the 4GB limit and then making the rest available above the 4GB limit. If you're curious, the register (in intel parlance) is often called TOLUD (Top of Low Useable DRAM).
Yes, furthermore, given modern OS designs on x86 architecture, a process cannot utilize more than 2gb (windows without /3gb boot option) or 3gb (linux, most BSDs, windows with /3gb and apps specially built to use the 3/1 instead of 2/2 split.)
However, that limitation does not preclude you from having a machine running eight processes using 2GB of physical memory each.
The processor feature is called PAE (Physical Address Extension). It works, basically, by adding an extra level of processor pagetable indirection.
Incidentally, I have a quad P3-700 (It's a Dell PowerEdge 6450) propping a door open that could support 8GB of RAM if you had enough registered, ECC PC-133 SDRAM to populate the sixteen dimm slots.
Anyways, here's a snippet from the beginning of a 32 bit machine running Linux which has 4GB of RAM:
[ 0.000000] BIOS-provided physical RAM map:
[ 0.000000] BIOS-e820: 0000000000000000 - 0000000000097c00 (usable)
[ 0.000000] BIOS-e820: 0000000000097c00 - 00000000000a0000 (reserved)
[ 0.000000] BIOS-e820: 00000000000e8000 - 0000000000100000 (reserved)
[ 0.000000] BIOS-e820: 0000000000100000 - 00000000defafe00 (usable)
[ 0.000000] BIOS-e820: 00000000defb1e00 - 00000000defb1ea0 (ACPI NVS)
[ 0.000000] BIOS-e820: 00000000defb1ea0 - 00000000e0000000 (reserved)
[ 0.000000] BIOS-e820: 00000000f4000000 - 00000000f8000000 (reserved)
[ 0.000000] BIOS-e820: 00000000fec00000 - 00000000fed40000 (reserved)
[ 0.000000] BIOS-e820: 00000000fed45000 - 0000000100000000 (reserved)
[ 0.000000] BIOS-e820: 0000000100000000 - 000000011c000000 (usable)
The title of that list should really be "Physical Address Space map." Either way, notice that the majority of the RAM is available up until 0xDEFAFE00 and the rest is available from 0x100000000 to 0x11c000000 - a range that's clearly above the 4GB limit.
Yes, it's running a bigmem kernel... But that's what bigmem kernels are for.
Oh, incidentally, even windows 2000 supported PAE. The bigger problem is the chipset. Not all of them support remapping a portion of RAM above 4GB.
fnord.
http://www.ida.liu.se/~abdmo/SNDFT/docs/ram-soft.html
This references an IBM study, which is what I think I actually remember but could not find quickly this morning.
"In a study by IBM, it was noted that errors in cache memory were twice as common above an altitude of 2600 feet as at sea level. The soft error rate of cache memory above 2600 feet was five times the rate at sea level, and the soft error rate in Denver (5280 feet) was ten times the rate at sea level."
My bet is that it is cerenkov radiaton as a high speed charged particle breaks the speed of light in the fluid in the eyeball.
Indeed, these flashes have pretty much already been identified as the result of Cerenkov radiation.
Looks like these truths are not so self-evident after all...
Well, if it takes your corporate IT staff that long to rebuild a computer, they're probably doing it by hand while putting out other fires, which is foolish. Better IT departments have standard images that have been made for and tested upon the computer models that they've standardized upon. Barring hardware failure, the result is a stable Windows environment with few software problems that aren't user-inflicted. In addition, rebuilding a system takes less than an hour: Gigabit Ethernet drops to the benches make backing up a system and restoring a clean image to it go very quickly. Rebuilds for purely remote users are a priority as well. They have access to their email and calendar via OWA, but not to any corporate systems that require VPN access, so getting their laptop repaired and back to them quickly is important: We try to get them repaired and sent out the day we receive them, and have been known to work Saturdays as well to get a system back to someone by the next Monday. We also maintain a hot spare pool: One laptop of every model that we support is on hand to overnight to someone whose laptop is broken. So, in all cases except where the hard drive is broken or the software on it borked, we can have a person up and running the next day. They then send us their computer, and we handle the warranty issues and return it to them.
We also don't permit anyone (ourselves included), to run Windows as Administrator or equivalent except for purposes of installing software or patching. While the computers are joined to our domain, remote/traveling users also have a local user account that is Administrator-equivalent whose name is "[their domain login name].local". They are given the password to it (which is different than their domain password) and told not to use it except to install software or in emergencies (but if they get to that point, they're expected to call: We have a person whose main job is to support remote/traveling users, and she's very good - not only is she an intelligent person, she's a skilled technician and knows our systems inside and out).
It sounds to me as though there are number of things going on: First, you're getting poor Windows installations. Secondly, there's probably a degree of PEBKAC going on as well. You say that you use Macs at home, so there's almost certainly more than a little resistance to using Windows stemming from attitude: "Macs are better and so I don't have to/won't learn how to use Windows". I've seen this more than once in our company: People that have Macs at home tend to be smug about them and pounce upon every problem (whether real or perceived) with their Windows computers at work. That's OK: After awhile you learn which people are your "problem children", and accommodate them as best you can.
In any event, I am sorry for your difficulties, and hope that they are remedied soon.