Salvaging Defective DRAM 220
An anonymous reader writes "Ever wonder what happens to DRAM that fails quality assurance testing during manufacturing? Turns out a lot of it ends up as 'downgrade' memory and ends up in OEM memory modules. Last resort: use it in an answering machine, where the sampled audio can be very tolerant of bit errors."
Comment removed (Score:3, Insightful)
I am seeing a lot of this (Score:5, Informative)
The downgrade ram has to pass further tests to insure the detours around the bad parts worked.
Granted, I probably wouldn't use this stuff in a mission critical server, but if you are buying for a mission critical server, you should be getting ECC registered with lifetime warranties anyway. Now for a small web or file server, or even a desktop, I'd use this.
Other people have mentioned memtest86. This program is your friend. Don't even bother with BIOS POST tests of RAM, just use this every once in a while if you REALLY want to find the problems. Too bad it won't run on my alpha server
Re:I am seeing a lot of this (Score:5, Insightful)
Re:I am seeing a lot of this (Score:3, Informative)
Actually, no that is not correct. Errors are caused by a localized defect which affects what is really (in human terms) a small point on the die. A particle of comtaminant, for instance, only a micron or two in size.
Ever wonder why NAND FLASH (used in Smart Media, Compact FLASH, etc) are cheaper than NOR FLASH (called linear FLASH, used for BIOS and other code storage, etc)? Because not only is it designed to be fault correcting, but the spec allows for up to a certain number of sectors to be completely bad (uncorrectable by the on board ECC bits). This means higher yeild since many more get to pass in spite of defects.
J
Re:I am seeing a lot of this (Score:3, Interesting)
The big question is:
Did you replace it with an identical type and speed of RAM? Or did it perhaps have fewer chips?
memtest86 may not detect overclocked RAM, and on some boards, if the RAM is double sided, the extra "stress" on the bus of a poorly desgined board may be enough to cause errors when reading or writing the RAM.
I've seen other strange effects that only happen to windows, such as a board that detects a full complement of 384 MB of RAM in the BIOS (1 each of 256 MB and 128 MB) but only 128 MB in windows. Moving the RAM about on the board would cause windows to _sometimes_ detect the rest of the memory. Swapping the 256 MB stick with another machine's 256 MB caused both machines to reliably detect and use the memory.
While I never bothered with memtest86, I'm betting it would see the same amount of memory as the BIOS.
Can you tell I hate modern memory modules yet?
Re:I am seeing a lot of this (Score:3, Informative)
Not true. All processes are subject to variation.
When a wafer is produced with hundreds or thousands of discrete die on it, some are always better than others. For instance, in the 5" process where the first Pentiums were fabricated, you could have a yield of 60%-80% good die with those 60%-80% spanning a whole range of marked chip speeds. Same process, same wafer, different mhz. Different price when sold.
If you've ever seen a fab in production, you would also see steps where manual (vacuum wand) handling is needed. Even in the filtered air of a clean room, the open movement of a wafer handled like this often leads to particles becoming affixed to the surface. The smaller the process (e.g. .09u vs..9u)the more damage a single particle can do.
Process washings with chemicals or pure water do a good job of assuring no (well, few) particles stay affixed, but even so, some steps of metrology show that all cannot be avoided.
Will a single particle hurt a single die? Maybe. Maybe not. It depends on where it lands and at what step in the process.
Once the die are tested for yield and function and sorted by this performance, they are sold in batches.
Not every die is tested completely though, but rather a restrictive set of "tell-tale" measurements are taken on most (at good fabs) and exhaustive testing done only on a small sample. Lots of statistical analysis helps know what to test and how hard to test it.
Move to the final assembler, and all sorts of production glitches can cause bad modules. Primarily though, either minimally qualifying RAM or random sample tested RAM makes it into generic modules. Still, all the other components, the circuit board, connectors and solder itself can contribute to problems.
In any case, the bad part in any chip is likely local because even minimal QA testing will eliminate obvious or widespread failures.
Of course, piss-poor process does yield chips more prone to failure by breakdown of the traces or local thermal failure due to bubbles, impurities, or poor assembly.
Re:I am seeing a lot of this (Score:2)
Basically, if you get random crashes/bluescreens/segfaults on your machine, it's probably RAM. Sometimes, it might just be something like gcc segfaulting every once in a while, with no apparent cause. Other times, it may be corrupted files, weirdness, bad archives, etc. It's actually quite similar to what happens when you overclock.
Re:I am seeing a lot of this (Score:5, Insightful)
There are a lot of peeps complaining about substandard ram. If you had RTFA, you'd realize that the downgrade ram is reconfigured to skip the bad parts in the chips, so that it comes out as a normal module. Just because there is a faulty bit or 10 in a modules, doesn't mean the reast of that module is bound to fail. It could just have been an imperfection in the silicon or the circuit process.
You have made a statement that makes it very clear you are a very educated layman, not someone in the field. What you've said is true to the first order, but not inherantly true.
Wafers have what can be measured as "defect density", and observe a phenomena called "defect clustering". Defects are not always hit or miss, open or short, some of them are latent or resistive. As the part ages (diffuses), electromigrates or observes hot electron effects, all parts will decrease in quality. Downgrade RAM, so to speak, would be most likely to have additional cells fail due to the above effects -- because it had failures that made it marginal in the first place. Testing methodologies at higher quality manufacturers build in guardbands to make sure that nobody ever experiences the defects when used in-spec. (This is why many overclockers lose their chips after only a year or two, they cause latent defects to surface and suddenly the chip won't even operate at nominal frequencies; the guardband effect also explains to a great degree why many chips can be overclocked in the first place.)
I'm not dis'n you, just trying to fill in a few more holes.
ECC worth it? (Score:2)
I've always been a bit dubious as to the value of ECC memory, and whether it might not just be a bit of a sales tactic. Yes, I realize that it's theoretically possible for solid state storage to spontaneously fail. But it's also theoretically possible for any number of other things to break, and spontaneous RAM failure seems very, very low on the list of things to worry about.
I can't help but think that ECC memory is more useful from a marketing standpoint than a practical standpoint.
Re:ECC worth it? (Score:4, Informative)
But it's also theoretically possible for any number of other things to break, and spontaneous RAM failure seems very, very low on the list of things to worry about.
Well, the thing about RAM failure is that, unless you do something like ECC, you won't detect the errors until it causes a crash. Probably, you'll lose some data to corruption first. The other thing is that RAM errors can be induced by bad power or other transient problems. Finally, it does happen, so better safe than sorry - you're spending $2k on a server, so why cheap out on a $50 part?
Re:ECC worth it? (Score:4, Informative)
Re:ECC worth it? (Score:2)
That can't be right, though. The system *bus* doesn't have ECC, and by virtue of its far greater area, would be much more vulnerable to errors induced by interference than the RAM.
Re:I am seeing a lot of this (Score:2)
I only buy Samsung ram for example because they know good quality. Also they have great ddram -3200 while other ram manufactors are not starting to introduce it.
I would rather pay an extra $15 per module then put up with blue screens of death and Linux kernel panics.
HP HP-UX memory. (Score:2)
Re:HP HP-UX memory. (Score:3, Informative)
Not a flame, just a clarification
Re:HP HP-UX memory. (Score:2)
Re:Cheap memory. (Score:2)
Re:Cheap memory. (Score:4, Informative)
Compaq and IBM both use Kingston Memory. They also like to jack up prices for their "rebranded" Compaq/IBM ram which is just really a Kingston module with an even higher price.
Toshiba uses Samsung. I'm not sure about manufacturers like Dell or Gateway.
Re:Cheap memory. (Score:4, Informative)
Re:Cheap memory. (Score:2)
Now there is a new excuse.... (Score:4, Funny)
"Oh you left a message on the answering machine, naah I didn't get it must be the defective DRAM chips they use. Now you've managed to track me down using a detective agency I'll be sure to send you the cheque next week"
*Long String of Curses* (Score:5, Funny)
Re:*Long String of Curses* (Score:3, Funny)
Re:*Long String of Curses* (Score:5, Funny)
Hi, this is ___ael. Give me a call at 55_12__. Talk to you latter.
Did I ever wonder? (Score:5, Funny)
No. I figured they forgot about it.
I figured (Score:2)
As a tip to Linux users with bad ram, try append="mem=fooM" where foo is an amount of ram below the broken area.
Re:I figured (Score:4, Informative)
Run memt86 and use the output for the badram patch for the kernel.
that will actually work and cut e vary minimal amount of ram out.
who needs IRC (Score:2)
My server, and its cheapass ram, thank you.
Re:I figured (Score:2)
Re:I figured (Score:3, Interesting)
Badram requires a simple download, dd to floppy, booting off the floppy, and making sure it started up okay. Then, you can leave it alone for a day while you let it make passes.
Anyways, assuming you are buying new ram and you want to be sure its okay, you'd have to do the same thing. And some older laptops have integrated onboard memory - the badram patch can work around that.
I have a 64M proprietary memory stick for an old toshiba laptop that will be arriving soon in the email - I will be using badram to test that when it comes.
Re:I figured (Score:4, Funny)
I had a great reply but... (Score:3, Funny)
-RickTheWizKid
Re:I had a great reply but... (Score:2)
If your name was D.A.R.Y.L., it might be...
Alternatively, you could use the... (Score:5, Informative)
Re:Alternatively, you could use the... (Score:4, Funny)
I don't want the bad ram patch.
You realize it is a mistake.
That would be a mistake.
You have better things to do with your time...that are less risky. You will go home and reconsider your life.
Excuse me, I need to go home.
bad ram patch for linux (Score:4, Interesting)
the url is:
[vanrein.org]
http://rick.vanrein.org/linux/badram/
Yes I was just sitting here (Score:3, Funny)
Buying ram on the internet..... (Score:5, Informative)
Re:Buying ram on the internet..... (Score:3, Insightful)
Re:Buying ram on the internet..... (Score:5, Interesting)
If only that was the worst of it.
Generic RAM is also in the habit of mis-reporting it's capabilities in SPD. The problem was so bad with 512M sticks back when that was the biggest available, many BIOS would automatically disregard SPD and choose the slowest settings when a 512M stick was detected.
Better brand names don't appear to have that problem.
Re:Buying ram on the internet..... (Score:2)
I have to disagree.
You can do quite well by simply buying very inexpensive RAM...that's rated higher than the RAM you're trying to get. Instead of buying brand name, expensive PC100 RAM, I bought cheap, generic PC133 RAM. No problems, all good...cheap.
Re:Buying ram on the internet..... (Score:3, Interesting)
Re:Buying ram on the internet..... (Score:2, Insightful)
If more people did a little research when they bought computers, or computer parts, they wouldnt have half the problems. Instead they listen to the sales people, or they buy the cheapest thing they can find and then wonder why their system locks up.
I wish more people would do this and not just for memmory, but for any big purchase. It's one of the truly great aspects of the internet, fast cheap research.
Re:Buying ram on the internet..... (Score:2)
Re: I bought that (Score:2)
I would still like to bye a gigabyte of name brand memory, but that would cost me well over $150 now.
Use memtest86 (Score:5, Interesting)
Re:Use memtest86 (Score:2)
About a third of all the machines I've delt with have had memory errors at some point in thier lifespan. Most of those errors were only found after a day of tests.
recycling the chips (Score:5, Interesting)
Maybe that explains a few things... (Score:2)
well (Score:5, Funny)
Re:well (Score:4, Funny)
just dont let your gf see it
No problem with that happening with most of the slashdot visitors.
Re:well (Score:2, Funny)
Dude, if you have a pc-board keyring fob, this problem is totally irrelevant.
Rob
Re:well (Score:2)
Re:well (Score:5, Interesting)
They were looking at the old 256k SIMM PCB (all chips removed) and asking "is that a computer chip"? Funny how they pointed at that and missed my Intel keyring fob with a real processor die on it.
Re:well (Score:2)
Memory keychains are nice for opening boxes, too. And to the grandparent poster, my girlfriend thinks it's cool.
Re:well (Score:2)
I should of explained my reasons for saying "dont let your gf see it", mine use to keep asking every so often "whats that again?" and after the 20th time you have to draw the line and part with it(the fob not the gf
Re:well (Score:2)
*note to terrorists, if wishing to hijack planes, use sharpened RAM sticks*
Re:well (Score:2)
Re:well (Score:2)
I've had 1/3rd of an old-school 32 pin SIMM as my keychain fob for quite a few years now (the ring goes through the hole.) The SIMM only had 3 chips on it, on one side, so it's nice and compact, and still had a nice geek appeal.
It's actually helped me find people with similar interests. I had my keys in my hand one day while getting a sub at subway, and the guy behind the counter (probably about 17) said something along the lines of, "Cool, old school RAM. Haven't seen that for a while." We then had a little talk about back in the day (I'm only 21), since there were no customers in the store.
Re:well (Score:2)
They ask to many questions, then every so often come out with "whats that again?", it can get tedious.
Some updates to the article... (Score:5, Informative)
There are some things in the article that are pretty out of date:
To reduce the test time, parallel chip testing usually is accomplished with eight to 16 chips in a row.
That's pretty low parallelism; there are memory testers out there that test over 200 devices at a time right now. And even the older, more common systems are probably testing 64 in parallel.
A special ink jet color marks the good dies.
This hasn't been true for years. Each device's pass/fail status is stored in a database, along with all other test results, and the whole process is automated enough that good die are binned out automatically. No need to physically mark the chip.
Due to the imperfection of the process, a percentage of the DRAM die contains some faulty cells.
That percentage is 100%. At modern memory sizes, you never get a perfect device without going through repair.
Re:Some updates to the article... (Score:2)
Can you please explain what do you mean by "repair"?
DRAM manufacturers include a small amount of extra memory on the die; there are a few "extra" rows and columns on the die. There is also a system of fuses which allows you to remove a row or column from the main array, and and also replace it with a row or column from the redundant area. These fuses are blown using a laser, prior to packaging.
The manufacturer tests the device, identifies the bad cells, and then "swaps" out a row or a column with a good row or column from the redundant area.
This is a little vague; manufacturers are very guarded about revealing the specifics of how they do this. Some manufacturers may have a smaller number of redundant cells, but have a very flexible system of row/column swapping. Others may dedicate more memory to the redundant system, but have a more restricted (but less complex) sytem of swapping in rows and columns. For example, restrictions on "even" or "odd" rows being swapped with the same type from the redundant array. In reality, the systems are usually way more complicated than just rows and columns (half rows, restricted use rows, pairs of rows, etc) but you get the idea.
In a modern DRAM device, every device needs to go through this process. (It's much cheaper to devote a small space to redundant columns and go through repair than to try to make a device that had a 0% cell failure rate.)
Use it for Linux ;-) (Score:3)
Needless to say I find this very cool indeed, but I'm not sure I'd want to run it on my high availability, mission-critical web server for a bank ;-)
Re:Use it for Linux ;-) (Score:3, Informative)
No. The idea of the patch wasn't to stop it crashing, you probably can't do that; the idea was to analyse it when the system booted and work around it then- it's perfectly possible to send the admin an email summarising it though.
There's something very cool about the concept of buying a tonne of memory for a tenth of the price and suddenly having a system with nearly four gigabytes of memory ;-)
Then again, isn't that what ECC memory is for?
No. AFAIK ECC memory can correct only bit errors within a word; but addressing errors slip right past it. The patch can handle addressing errors, blocks that just don't work, blocks that mirror back to the same location etc. etc.
Re:Use it for Linux ;-) (Score:4, Interesting)
Bzzzzzzt! Wrong, buddy!
I remember working with a DEC VAX 11/750. It had roughly the processing power of a 286, though it's hard to compare the two.
It was the size of a large, commercial dishwasher, and had a stack of other boxes that together were about the same size that were the three 350 MB Hard Drives.
The fault tolerance on this computer simply boggles the mind of anybody used to the Linux or Windows world.
It would dynamically detect and remap areas of the hard disks going bad. It would dynamically detect, correct, mark, and log areas of RAM that were going bad - it would even tell you which CHIP on the memory card (about the size of a dinner plate) the error was on, with zero downtime, while it was running!
It used a method not unlike ECC to determine "bad" and would map around bad RAM or disk sectors as a basic function of operation.
It was so good, that one time, when it crashed (due to the air conditioner failing) that when we brought it back up, most people's sessions were preserved on their terminals, and just started working again, right where they left off! Despite the computer having been OFF for several hours!
Sorry, but you haven't seen fault tolerance in a computer until you've seen it on an older DEC VAX. I can only wish that anything like that was available today.
It probably is, but I sure can't afford it.
Re:Use it for Linux ;-) (Score:2)
Uh no. You may be able to harden the OS against a memory failure but this won't be a 100% cure against all memory failure.
How to identify DIMMs using bad RAMs (Score:5, Informative)
DRAM chips are usually have either 4, 8 or 16 bits per word. In order to construct a DIMM, 64 bits are needed. This means that with 4 bit DRAMs, you need 16 chips, with 8 bit DRAMs you need 8 vhips, and with 16 bit DRAMs you need 4 chips. usually you will see only the 4 or 8 bit DRAMs, because these occupy less board area for the same capacity. 16 bit DRAMs are only used for low capacity DIMMs.
When your DIMM supports ECC, it's 72 bits wide, which makes it more complicated. Usually its made of 18, 4-bit chips, or 9 8-bit chips.
(back in the 30 and 72 pin SIMM days, when memories were 8 or 32 bit wide, you could see ECC SIMMs that use 3 chip for 2x4+1=9 bits, or 2x16+4=36 bits).
If you see DIMMs with 12 chips, This is usually a cheap OEM SIMM using partially good DRAMs.
The Best way to identify such a DIMM, is to write down the marking on ALL the chips on it, and look them up in the internet. You then sum up all the DRAM bit widths, and see what you come up with:
If its 64 bits, its a normal DRAM.
If its 72 bits, its probably an ECC DIMM.
If its more, it's probably a DRAM using partially good DRAMs.
Does it get worse? (Score:2, Interesting)
Dead pixels on LCD screens are like this, if you don't have any dead pixels, you'll never get any. But how about RAM?
Re:Does it get worse? (Score:4, Informative)
Re:Does it get worse? (Score:2)
Re:Does it get worse? (Score:2)
Nope...I've tested memory testers professionally. The memory (or a related memory subsystem/connector) is almost always at fauly...not the tester. If you want verification, I'd be glad to charge you for it...
Clive sinclair did this in the 80's. (Score:2, Interesting)
You can get an extra 16k on most speccys by soldering a couple of links.
Lost messages (Score:2)
Eventually, I learned my lesson: If it ain't broke, don't fix it. My mechanical answering machine is now 18 years old and running fine. I have no plans of ever replacing it again.
Re: Central servers at the telco (Score:3, Insightful)
The services at the telco let people leave messages when I am on the phone.
Uses for defective DRAM (Score:2)
Alternate subject (Score:4, Funny)
Re:Alternate subject (Score:2)
People might randomly call other people to leave copyrighted songs on their answering machines!
I just figured it was at Fry's (Score:5, Informative)
What's worse, before they would take it back, they wanted to "test" it, testing being limited to a couple runs of PC-Doctor, which is totally lightweight.
To make a long story short, they refused to take it back the first time, later it blew up my motherboard. They replaced the motherboard (it was part of the package) and sent me home, where I discovered my Athlon XP was also damaged. I took it up there, and they wanted to run PC-Doctor on it, but the "technician" (hah!) cracked the CPU while putting it in a "test board," so "oops, I guess we're replacing that."
P.S. One of the guys at the return desk who I got to know quite well told me, when I asked him why the "test boards" they were using always changed, that he thought they were boards that belonged to customers. Whether that meant boards in for repairs, or returned boards, I don't know or care - either is bad news.
P.P.S. This was at the Fry's in Wilsonville, Oregon. There is also an idiotic troll in the service department there who, after ignoring me waiting at an empty counter for 10 minutes while he chatted on the phone, wanted to charge me for a "missing" monitor stand on a monitor I was returning, refusing for 15 minutes to look in the bottom of the box under the styrofoam because monitor stands always come attached to the monitors, didn't you know? He finally looked when I demanded to talk to the manager, and of course it was there. I had a long discussion with the manager anyway over his, and their, incompetence (I reminded him of the memory fiasco) but the troll was still lurking there the last time I dropped by for consumables, which is all I will ever buy from Fry's, now. You can't miss him - he looks like he'd feel more at home in a raincoat, instead of his cheesy lab coat, roaming a playground on a sunny day.
Re:I just figured it was at Fry's (Score:2)
Well, when I got the replacement memory, I paid the upsell price for overly-marked-up Mushkin, which seems to have worked out fine. But as far as the memory goes, the original faulty sticks were no-name but had a lifetime or one-year or whatever guarantee, not the 90-day. They were just being jerks wanting to test it.
My first mistake in all this was thinking that their "package deal" was really all that much better than what I could have done through the Internet, and for wanting my new system parts right away instead of in a couple days.
Really, when I lived in Oregon, if I'd have had a good selection of vendors locally, I wouldn't have been at Fry's, anyway. Also, Oregon has no consumer sales tax for regular goods, so Internet price + shipping was often close enough that I stopped bothering with Pricewatch and IBuyer for most things. But Fry's, unfortunately, had the widest selection that I knew of.
The only reason I can think of is expediancy... (Score:2)
Crucial (Score:2)
I just won't take their word for how many sticks can fit in my motherboards, because they've been wrong twice for not counting the banks on the sticks they suggested.
I've tried Mushkin, but only because they were the best named sticks Fry's had when I was there, and the only 2-3-3 PC266s in stock. Mushkin's cool, but historically way overpriced. I wouldn't even have recognized the name except for the advertising on Anandtech.
Re:I just figured it was at Fry's (Score:2)
Ooh, look at the Anonymous Coward trying to lecture me over this.
What are you, an object lesson?
To be quite honest... (Score:4, Funny)
I'm never buying OEM ram again (Score:4, Insightful)
DRAM Testing (Score:5, Informative)
There is no way under those pressures that a company will make a perfect device. They build "redundancy" into the devices. This redundancy is used to fix the devices before they ship out of the factory (usually you can't fix the device after you package it). So most all DRAMs had some failures that were fixed during testing of the device.
Most of the memory manufacters test to JEDEC specifications. These specifications may be too tight for some applications. For example, in a well ventilated case, your RAM won't hit 90 degrees C, but that is where the manufacters test it.
So the "recovery" market buys bad devices from the major manufacturers and retests the to loosen specs. Some devices pass the loosened tests and are considered good. Other devices fail, but only in a single I/O. These devices are sorted so that custom DIMMs can be made that uses extra devices to make use for the bad I/O's.
As far as using your POST memory test to figure out if you have bad RAM, forget about it. A POST memory test is like making a visual inspection of a jet engine... necessary but not sufficient. There are many failure types in DRAM. The easiest are stuck-at's. A stuck-at is a bit that is stuck at a value. A POST will find this (and probably not much else). Other failure mechanisms are:
- cell coupling (program an bit and another bit also sets)
- column coupling (cell is correct, but when trying to read it, neighboring column makes other column read incorrect)
- bank noise (activating/precharging another bank causes read/write on another bank to fail)
- retention (how long will a cell keep it's state until refreshed)
- sense failures (sense amp can't measure the voltage differential when a cell is read)
And bunch of others. These are only the device errors. This doesn't take into account power problems, bad connections, leakage between traces, etc.There are three key enablers that help the manufacturers find these device errors.
First are test modes that manufacturers put in their devices. Test modes help the manufacturer cut down on test time and artificially stress the device to pull out failures quickly. These test modes are different between manufacturer and can't be accessed in the computers. Accidentally putting your RAM into test mode would be a very bad thing. There is nothing that a POST test (or other tests from the computer) can do to access these test modes.
Second is controlling the temperature. DRAM's are very temperature sensitive. A DRAM that passes when you first turn on your computer, may fail once the computer gets hot. Obviously right when you turn the computer on isn't the right place to do tests that are sensitive to temperature.
The third thing you need to know is how the cells of the memory are laid out into the addresses and I/O's of the device. Each device design is different. Even in the same manufacturer the mapping of outside addresses to physical rows and columns will not be the same. To make matter worse, the devices have been repaired, so each device will have the "spare" rows and columns in different places. So each device of each DIMM will have a different mapping of outside addresses to internal locations.
Why is this important? Consider the cell coupling case. Two cells share charge. If you don't know which cells are adjacent, you have to read every other cell to make sure it didn't change. So to test every cell (N) you have to read every other cell (N-1). That means this "pattern" is going to take ~N^2. Now you have to do the same thing with inverted data. Make that 2N^2. Lets just think about a 256Mbit device (common on 256MByte DIMMs). Lets assume we can access addresses at 100MHz (we can't go that fast, but it doesn't matter). This pattern takes somewhere around 45 years... for one device.
So it is impossible to fully test a memory device unless you are the manufacturer. This includes the memory recovery people, UNLESS they have a deal with the manufacter to share the layout of the device.
Now on the other hand, most of the memories aren't all that scrambled up. And even memories that are heavily scrambled still have some regular structures. So if you assume that the external memory addresses directly map to internal, you can test quite a few of the couplings. You may get lucky and find the problem. This is why exhaustive memory tests sometimes find a problem with the bad memory. It also explains why the tests run so many different data patterns at the memory.
What can you do? Buy good memory from the top manufacturers (there are some really smart people who put together these tests for the manufacturers). Make sure the names of major manufacturers are stamped on the chips. Micron, Samsung, Hynix, and Infineon are the big four. Beware of the off brands.
Note: Part of this comment was copied from a post I made at Macintouch. They had a thread on bad RAM a while ago at http://www.macintouch.com/badram01.html [macintouch.com]
tha~s a re_lly go@d article (Score:4, Funny)
Badram (Score:2)
You can use memtest to generate a list of bad areas in ram, and the badram patch reserves those blocks of memory on boot such that nobody can ever use them, effectively giving you a working stick of ram, only a little bit smaller than it is marked for.
If you're like me, you have a couple of cheapo sticks from who knows where that don't exactly work, and this patch is perfect for reviving those sticks.
Dude, yer gettin' a DELL (Score:2)
Re:Dude, yer gettin' a DELL (Score:2)
They are more expensive then the el-cheapo ones but they only use things like crucial or micron ram, asus motherboards, reliable intel chipsets and so on.
Dell makes alot of money from bussiness and small bussiness customers and support and quality is critical for them. Other oem's like gateway are another story. If my parents wanted a new computer I would most certainly recommend a dell.
They also get bulk discounts for being so big so buying a dell with all the higher quality components is not that more expensive then building your own pc using cheap parts.
Someone called for you. (Score:2)
555-653
Re:Ever wonder? (Score:4, Funny)
They end up on earth.
I have it (Score:5, Funny)
It's in my closet. All of it. The whole market. I'm waiting for the entire tech market to crash, so I can flood the market.
Re:What about the rest of the computer? (Score:5, Insightful)
Re:What about the rest of the computer? (Score:2)
Not me. That's what friends and charities are for. I'm about to get rid of a few system boards, speakers, 1-2 Sun boxes, SCSI equipment (CDs, small drives, cables), and excess cables (network, power, otherwise).
The oldest thing I have is a 1.2M 5.25 floppy drive...strictly for data recovery.
Re:What about the rest of the computer? (Score:2)
Re:What about the rest of the computer? (Score:2)
I'm pretty sure that it is all being sold on eBay right now.
Re:uh, no (Score:3, Funny)
Sell it all and wait to see what the consumer returns.
Re:uh, no (Score:2)
Re:I have this problem right now! :( (Score:2)
Re:I have this problem right now! :( (Score:2)
I've got an Abit BX6 that was working just fine a month before it suddenly started dying earlier and earlier in the boot process until it wouldn't boot at all. I've got a Soyo BX board I bought used that seemed to work fine when I first got it and was dead as a doornail a day later. Just because something was working is no guarantee that it still is working. The best way to screw yourself over when troubleshooting is to make assumptions.