|The term CPU is frequently mis-used. |
The computer case most of your computer components are in is NOT a CPU, it's just a computer case.
The CPU - Central Processing Unit - a.k.a. the micro processor or processor - is the most complicated integrated circuit chip on your computer, usually it's the largest one, that usually is installed in a socket on the mboard (or it's soldered in).
Where / when are you seeing these varying ram amounts?
Are you seeing that
- on the screen while booting?
- in the mboard's bios ?
- in System Information in Windows ?
System Information quotes several ram (memory) amounts.
(E.g. Start - Run - type: msinfo32 , click OK or press Enter.
Look on the right side on the first screen you see.)
Total Physical Memory is the one that shows the amount of physical ram installed, or that minus the amount used by onboard video, if you're using onboard video, depending on your bios.
Does your mboard have onboard video and you're using that?
If it does / you are, some bioses subtract the amount of ram that is shared with the onboard video from the total amount of ram installed, some don't. If the bios does subtract that amount, the same amount as shown while booting is shown in System Information in Windows, as Total Physical Memory. E.g. if the onboard video is using 64mb, 256 - 64 = 192mb available for Windows.
It's extremely rare for ram that was working fine previously to suddenly go "BAD". Almost always, when you have a ram prblem, either the ram has a poor connection in it's slots, or you're trying to use ram that is NOT 100% compatible with using it in your mboard.
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:
For a laptop, or netbook, you must remove both its main battery and AC adapter before you do that.
For a brand name computer, see the Owner's or User's manual if you need to - how to remove or replace the ram is usually in that - it may already be in your installed programs. If you can't get into Windows, it may be on a disk that came with the computer, or you can go online and look at it or download it - it's in the downloads for your specific model.
If that doesn't help....
Have you changed which ram module(s) you have installed since the ram amount was last correctly detected all the time?
Not all ram that you might think should work in your mboard is compatible with using it in your mboard.
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 (part numbers) 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.
If your ram passes a ram test, it's working fine, even if you can't determine whether it's listed for your mboard or system model anywhere
If you do a ram test, do that AFTER having tried cleaning the contacts and making sure the ram is seated properly - otherwise any errors found may be FALSE.
If the ram is incompatible with the chipset, or on more recent computers, incompatible with the memory controller built into the cpu, it will likely FAIL a ram test - that is NOT a true indication of the ram being faulty - there is probably nothing wrong with it, and it will pass the test if installed in a mboard it is compatible with.
NOTE: Sometimes incompatible modules (or matched pairs) won't work properly when more than one is installed, but will pass when by itself.
If you want to try a memory diagnostic utility that takes a lot less time to run a full pass than memtest86 does, this one is pretty good - Microsoft's
Windows Memory Diagnostic:
It can be toggled (press T) to do a standard or a more comprehensive set of tests - use the default 6 test one first - if it passes one pass of that, use the latter one. A few of the tests in the latter set are intentionally slower.
If you don't have a floppy drive, see the Quick Start Information at that Microsoft link for how to make a bootable CD of the Windows Memory Diagnostic (you need Windiag.iso - you don't necessarily need to use the program they mention to add it to the CD).