'have 2x 4GB memory sticks DDR2 but my computer is only reading 2.50GB but when i put 1x 2GB and a 1x 1GB it reads 3GB '

'I am running 32-bit windows 7 '

The 4gb virtual memory address limit for 32 bit operating systems.
An example of 3gb working better than 4gb in a 32 bit operating system.

See Response 6:
http://www.computing.net/answers/ha...

Press harder when inserting modules into the memory slot. We get multiple calls about memory not working when the computer just needs to be plugged in! If your system is only reading half of the new module's memory, and the module has chips on both sides, then your system probably will only recognize single-banked or single-sided.

• See More: Computer is not reading my full memory. Ive done everything, but its only reading the first white slot for ram and none of the other 3. It was working.
• Apr 13, 2017  So I have 16GB RAM. After upgrading to Windows 10 however it says I only have 8GB. When I look in task manager it seems to know I have 16GB but for some reason only using 8Gb of it and for slots used it says 2 of 4 when I'm using all 4 RAM slots. I'm not techy at all but if somebody could explain to me why this is it would be appreciated. If it is something like just a broken RAM stick then.

You often have more ram available for the user and Windows when you install 3gb rather than 4gb or more.
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Check Memory Slots

You may have not have any programs that benefit from more than 3gb of ram.

Memory Assessor
How much memory do you really need?
http://www.kingston.com/tools/asses...
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Which Ram Slots

A better explanation I've seen.

Ram Slots Not Working

If you have a 32 bit operating system and you have installed 4gb (or more) in the mboard, the amount of that ram available to Windows and the user is
4gb minus the amount of ram your devices require or have.
E.g.
- minus the amount of ram shared with onboard video if you're using that
- and/or - minus the amount of ram your dedicated video card installed in a slot has.
If you have more than one video card installed in a slot, it would be minus the ram for all of them.
(and = Some mboard main chipsets have Hybrid video capability. If you have a PCI-E X16 video card installed in a mboard slot that is supported by that feature, it's often the default for both the onboard video and the video on the card to work at the same time, unless you change default bios Setup settings. In that case it would be minus the ram for both of them.)
- minus the amount of ram your sound adapter has, if that applies - e.g. sound cards installed in a mboard slot often have ram
- minus the amount of ram any other devices have, other than hard drives and optical drives, if that applies.