3.3v DRAM Disguised as 5volt

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Hawaii Cruiser's picture
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Joined: Jan 20 2005
Posts: 1433

I won an auction of RAM which included this stick of 128mb DRAM. The seller had it listed as 5volt, but when I looked up the chip numbers it turns out it is actually 3.3volt DRAM. As you can see by the photo I took of it next to a regular 5volt DRAM, the notches are aligned correctly for 5volt slots. The chip number is mt4lc8m8b6 and the specs can be found in a PDF here:
http://download.micron.com/pdf/datasheets/dram/D19_2.pdf
The seller claims that he had it in his 8600 for a long time before he took the machine apart and sold the parts and never had any problems with the RAM. The PDF says that the max supply voltage is 3.6volts, so I don't get it. If it's notched for 5volt then it must be designed for 5volts. Is this RAM safe to put into a 5volt slot?

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coius's picture
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Joined: Aug 25 2004
Posts: 1975
hey!

I'll take the ram and actually give you bonified ram that shipped in an 8600. I have 3 of 'em and don't know what to do with them, or i could just send you the lot. They were given to me by a client that the 8600 had the hard drive go bad, so they threw the thing out. I was able to persuade her to give me the ram. so... I can send you 3 ram sticks, and 2 of them can be used in interleaving. So PM me if you want them

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See my PB540c 33Mhz serve a website! http://yui-ikari.coius.info/

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Joined: Dec 20 2003
Posts: 57
Re: 3.3v DRAM Disguised as 5volt

Hawaii Cruiser wrote:

The seller had it listed as 5volt, but when I looked up the chip numbers it turns out it is actually 3.3volt DRAM. As you can see by the photo I took of it next to a regular 5volt DRAM, the notches are aligned correctly for 5volt slots.

The PDF says that the max supply voltage is 3.6volts, so I don't get it. If it's notched for 5volt then it must be designed for 5volts. Is this RAM safe to put into a 5volt slot?

Seven years too late, but in case someone else comes along reading this cluster of threads...

In the late days of the x500/x600 machines, many FPM/EDO DIMMs were made using 3.3V parts. Typically, the I/Os on the memory chips were 5V tolerant, and the manufacturer would sneak a tiny voltage regulator or two onto the DIMM to reduce the 5V supply voltage to 3.3V.

I don't see a voltage regulator on the photos of this DIMM, but the photos are pretty small. It's also possible that the manufacturer just did a ballpark calculation of the current consumed by the parts, and put a series resistor in place to reduce the voltage to around 3.3V.

The strange bit is that the Micron data sheet doesn't seem to indicate that the IOs on these chips are 5V tolerant, but perhaps they are.

Anyway, the gist is, that many 5V DIMMs were built with 3.3V parts, and they seem to work fine.