Salvaging Defective DRAM

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."

Comments

bad ram patch for linux

[Anonymous Coward]

Summary: This page proposes an approach to support RAMs with defective addresses, This may open interesting business perspectives, where those RAMs can be sold under a white label for less money rather than discarded of without any profit.

the url is:

http://rick.vanrein.org/linux/badram/

Use memtest86

[Black Parrot]

...and read its documentation to find out how to make Linux skip any defects it finds.

recycling the chips

[v1]

I recall seeing an article awhile ago where companies were buying defective memory, and running them in these external testing units,which would identify which chip(s) on the stick were bad. I'm assuming they'd then unsolder the bad chip and recover one from another module. At that time some of those sticks had 8 chips on each side, so you could recover 15 good sticks from 16 bad ones. Considering the price of memory a few yrs ago, it was probably a worthwhile venture. Nowadays though, it's probably not worth anyone's time.

Good idea

[Anonymous Coward]

Audio quality on answering machines dont have to be that great. Because of the ability to resell defective DRAM overall costs of both answering machines and high quality DRAM has gone done.

Re:Buying ram on the internet.....

[$$$$$exyGal]

Back when I was in college, I bought a relatively expensive 128MB memory chip from a company I found in a magazine. The warranty was only for like 30 days, but it was like $20 cheaper than their competition. I called them up, and received the chip about 30 days later. I didn't even try to put in the chip for a couple weeks because I needed a friend to help me out (hardware scared me back then, and still is one of my biggest weaknesses).

Once I did finally get the chip in my machine, it never worked. I called the company one time before the warranty period was up, and they gave me the rigamaroll (waiting for support for several days, etc). I never did get the chip to work, and I never did get my money back. I've chalked this one up to my own stupidity.

Re:Buying ram on the internet.....

[Ogrez]

Im a sysadmin by trade... and although I might chance 90 day oem ram if the price is right in my home machine, in my production servers I use Crucial, or Kingston. As far as the average consumer... How do they determine if a car is good, what criteria do they use to determine what new stove to buy? They do some research..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.

Does it get worse?

[Looke]

I wonder, does RAM faults develop over time, or are they introduced in manufacturing? That is, if you have some bad RAM, and correct it with Linux BadRAM, can you then be reasonably safe you won't get more faults?

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?

Clive sinclair did this in the 80's.

[Anonymous Coward]

The Sinclair Spectrum used half working 32k memory chips for cost reasons. In the later models, the computer used the same system, even though by then they were using mostly working chips as the cost of memory had fallen.

You can get an extra 16k on most speccys by soldering a couple of links.

Re:Buying ram on the internet.....

[sjames]

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.

now i know...

[Anonymous Coward]

i had a digital answering machine. funny thing with this was that the outgoing message recorded sound quality used to degrade over time! to this date, i have no idea how this could be the case. was it because of defective RAMs?

Re:well

[wik]

Not to mention, give you hell at the airport. The security guys in Pittsburgh told me to put my keys in the little bucket, then when they looked closer, told me to put them through the X-ray machine.

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:I figured

[dasunt]

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 am seeing a lot of this

[shepd]

>When I replaced one of the sticks, all the problems went away.

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:Use it for Linux ;-)

[mcrbids]

No. The idea of the patch wasn't to stop it crashing, you probably can't do that

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.