I want to increase RAM on my emachines M5405 notebook from 512MB. Manufacturer and other references tell me the max RAM is 768 MB. However, one internet seller offers a 1 GB stick and guarantees compatibility. Is this possible...what would happen if I used 1 GB?

Hi welcome to the forum It looks like it should work from what I can see it takes a max of 1.2Gb ram
eMachines M5405 Memory

Thanks for the link madmatt. However the link is to the one vendor saying max RAM is 1.2MB when I searched using manufacturer and model. When I used the "check your computer" tool it said unable to provide an exact match. 3 or 4 other sites all tell me max RAM is 768MB. Currently there are 2 slots, 1 256 non-removable and 1 256 removable. If I gamble on the 1GB stick...I can think of 3 possible outcomes; 1) it works at 1.2GB, 2) it works but only uses 512MB of the 1GB, and 3) it doesn't work at all leaving me with only 256MB of the non-removable memory or worse, doesn't work at all. Do you know whar happens if I exceed the manufacturer' specs?

All is well! The 1GB stick works fine...Thanks madmatt.

I'm still curious, is there any limit to the amount of memory that can be installed in a PC/laptop provided that the stick fits in the slot and everything else is compatible?

Yes, there is a limit. Some motherboards can only handle so much RAM. Also Windows 32-Bit can only handle 3GB at the maximum. However the 64-Bit Windows can handle much more than that.

actually, the 32 bit will take 4 gigs, but you are correct in that it will only use 3 of them......one of the weirder vagaries of the OS, I think.....