|"....it looks like you are talking about PC100 or 133 SDRAM which has a pin count of 148."|
StuartS's info is relevant, except 148 should be 168
"....after the mother bored on my E-machines 420 randomly died."
With emachines desktop systems, it's a lot more likely the el-cheapo power supply became defective and fried the mboard, rather than the mboard randomly failed, especially if the make of the PS is BESTEC.
SD by itself is most commonly properly used to stand for Secure Digital, e.g. for a Secure Digital memory card for a camera.
You should probably be referring to SDram (Synchronous Dynamic ram) which is what is used in a computer's ram slots on a mboard. SDram is also DIMM ram (Double Inline Memory Module), but DIMM ram isn't necessarily SDram.
DDR ram and above is also SDram but that is usually omitted when referring to it in brief descriptions.
"The memory for the packard bell fried some time ago,"
It is extremely rare for ram that worked fine previously in a mboard to spontaneouly go "BAD", and even if it does, it is even more unlikely more than one module would go "BAD" at any one time.
If ram is actually bad, that is very apparent when it is first installed. If a new module is actually bad, which is extremely rare, that will be apparent right away - it's extremely unlikely that would be apparent a while after it has been installed.
In almost all cases, when ram isn't working properly, it's either not compatible with being installed in that mboard, or it's got a poor connection in it's ram slot.
A common thing that can happen with ram, even ram that worked fine previously, is the ram has, or has developed, a poor connection in it's slot(s).
This usually happens a long time after the ram was installed, but it can happen with new ram, or after moving the computer case from one place to another, and I've had even new modules that needed to have their contacts cleaned.
See response 2 in this - try cleaning the contacts on the ram modules, and making sure the modules are properly seated:
Ram can certainly be damaged by something the user did...
- if they installed or removed ram on an ATX mboard without disconnecting the live AC source to the PS/mboard
- by them installing the ram backwards in the ram slot and then powering and trying to boot the mboard - that fries both the module and the ram slot instantly and the mboard may never boot again even if the damaged ram slot is cleaned of the produced melted plastic and carbon deposits.
However, in most cases, those causes are not what caused the ram problem.
Ram can be damaged by events not under the users control, such as by a power failure event or other AC power event that produced power spikes or surges, or by a lightning strike on the AC power grid, or by damage caused by a failing power supply, but usually those events don't hurt the ram.
What Jennifer's too brief Response 1 is trying to point out is you may find out which ram will work for sure -- is compatible with it - at the Crucial web site.You use the particular mboard model or brand name system model to look up which ram will work.
StuartS's info about finding out which ram is required in the mboard manual is also a good pointer, however, it can be difficult or impossible to find a mboard manual for a brand name system, and sometimes the info in the manual about the ram was later updated, often because you can actually install certain larger modules than the manual states - the web sites where you can look up which ram works for sure have the most up to date info.
Ram that works in another mboard , or any ram you buy or have lying around, may not work properly, or sometimes, not at all - even if it physically fits and is the right overall type (e.g. SDram, DDR, DDR2, etc.; PCxxxx, xxx mhz) for your mboard. In the worst cases of incompatibilty your mboard WILL NOT BOOT all the way with it installed, and the mboard may not even beep - the ram has to be compatible with the mboard's main chipset, or in the case of recent mboards, compatible with the memory controller built into the cpu.
If you still have the ram that was installed when the system worked fine, try installing just that ram.
See response 5 in this for some info about ram compatibilty, and some places where you can find out what will work in your mboard for sure:
Correction to that:
Once you know which module ID strings work in your mboard, you can get them from anywhere you like that has ram with those ID strings.
If you have brand name ram, it is usually easy to look up whether it's ID string is in a list of compatible modules found by using your mboard or brand name system model number.
If the ram is generic, that may be difficult or impossible.
It is easy to test for incompatible ram that has caused your mboard to fail to boot.
Make sure you have a speaker or speakers or the equivalent connected to the mboard so you can hear mboard beeps (see your mboard manual if you need to).
Remove the AC power to the case/power supply.
Remove all the ram.
Restore AC power.
Try to boot.
If nothing else is wrong, you will get no video but you will hear a pattern of beeps that indicate no ram is installed, or a ram problem.
E.g. for an Award bios or a bios based on one, that's often a beep of about a half second, silence for a half second, a beep of about a half second, silence for a half second, continuously.