How does increased RAM make games run smoother? Does it increase the fps?
Is there a significant difference between PC2100 512MB or PC2700 512MB?
And also between 256MB PC100 SDRAM and 512MB PC100 SDRAM for games?

I am not certain about performance differences between the 2100 and 2700...

In regards to your second question - the more memory you have the more address spaces you will have for your software applications. To keep it simple:

Everything that happens in your machine requires the cpu to swap things in and out of memory space. Therefore, if you have 256 megs of additional address spaces available, more things can run at the same time.

The easiest and least expensive update you can do (generally speaking) is add memory.

The difference between DDR2100 and DDR2700 memory is higher bandwidth. DDR2700 is faster than DDR2100, and the higher the bandwidth the memory bus has, the faster it can process and page information in and out of memory. In other words, DDR2700 will be faster than DDR2100, but by how much, I don't know, b/c I've never compared the two.

To carry on further on Sephiroth's reply, here is how bandwidth is calculated:

Each DIMM module (SDRAM of DDRAM) is 8 Bytes wide. So basically each module is capable of 64-bit addressing (1 Byte = 8 Bits).


Peak Bandwidth = (Memory Bus Width) x (Memory Bus Speed) x (Operations/Clock Cycle) .

So taking the above into consideration,


PC2100 bandwidth = (8 Bytes) * (133 MHz Memory Bus Speed) x (2 Operations per cycle) = 2,128 MB/sec = 2.1 GB/sec bandwidth rate

PC2700 bandwidth = (8 Bytes) * (166 MHz Memory Bus Speed) x (2 Operations per cycle) = 2,664 MB/sec = 2.7 GB/sec bandwidth rate

Hope the above explains bandwidth calculation!