Motherboard: Intel 845GVSR
Slots: 2
Free: 1
Current RAM: DDR 256 MB PC266 MHz
OS: Win XP

Want to add 512 MB to the 256 MB.

Following are my queries:
1) Compatible RAM speeds with the motherboard?
2) Will using RAM of higher speed alongwith the existing 266MHz speed RAM harm the motherboard?
3) What does backward compatible mean? If it means that higher speed RAM can be used with an older lower speed RAM, then which speed will the combination work at?

One more query, I have Intel Pentium 4, 2.00GHz. How do I find out processor's system bus frequency?

Please help me.
Regards,
Yossi

If you're going to keep the 256MB DDR266 (PC2100), any RAM you pair up with it will be forced to run at DDR266 speed (133MHz). In other words, if you were to install a 512MB stick of DDR333 (PC2700) which is capable of 166MHz, it will automatically underclock to DDR266 speed to match the lower rated stick.

http://www.intel.com/support/mother...

Your 2.0GHz P4 runs at 400MHz FSB with a CPU frequency of 100MHz. The clock settings are 20 x 100MHz. The proper RAM to run with this CPU is DDR266 (PC2100) @ 133MHz, or higher rated RAM underclocked to 133MHz.

http://www.intel.com/pressroom/kits...

If I discard the current stick, which one should I buy?

I mean which will be compatible with the MOBO and give the best performance? As per the link you have given, it says 333, 266 and 200 MHz DDR SDRAM. So can I discard the existing 266 and use a new 512mb 333 stick?

What will happen if i use 400? Is it like because i have P4 2GHz, my FSB is 400, so i can use max 333 speed ram? Have i got that right? Here's an extract from my MOBO details on Intel site:

FSB 533MHz = use ddr333 or ddr266
FSB 400MHz = use ddr266 or ddr200

Thank you for looking into this.

Regards,
Yossi

Specs of my existing RAM:
DIMM1 256 MB PC2100 DDR SDRAM (2.5-3-3-6 @ 133 MHz) (2.0-2-2-5 @ 100 MHz)