can 2 different brand of ram cause problems

[bboysil]

I have 2x512 MB DDR2 of Sycron memory 5-5-5-18 but i am running them at 4 4 4 and they work great.
If i get another 2x512MB DDR2 800 TwinMOS Twister 8D25JK-TW
(5-5-5) but these don't work at 4 4 4
can there be any compatibility issues (if i install all 4 memory cards and run them at 5 5 5) because they are different brands?

 

[jitpublisher]

Very simply, yes. Even going from 2 to 4 sticks can require slower settings even if all 4 sticks are exactly identical.

 

[bboysil]

I am interested in more details. What kind of compatibility issues arise? (except that i have too loosen the timings)

 

[jitpublisher]

If you loosen the timings, and your machine boots, that's about all there is to it. Make sure all the memory is rated at the same voltage, run memtest for a while to make sure you get no memory errors.
HOWEVER, there is no guarentee that the different sticks will work together. Some boards simply have problems running some types of memory-some types of memory have problems working with other types of memory, it's not a common problem, but it can arise. It is always best to match memory, but many, many people run different brands and speeds with no problem at all.
Check you motherboards web site for recommended types of RAM.