Memory timing calculation

I have searched O/C but I don't think I am searching right. What I want to know is how a person can check how fast a ram stick can go...

aka 6ns chips how high will these go?

Reason Crucial has 6ns rated at pc2700 while kingston is using 6ns on pc3200

I believe that the 6ns refers to the design specifications the individual chips are made to run at (pretty sure JEDEC determines this) and the PCxxxx rating is more of a PR rating, if companies take selected 6ns chips that run faster they can make ram that's better than 6ns. just because a chip is 6ns doesn't meen it can't really run at 5ns, kinda like processors.

anyway take 1/6ns or 1/ (6*10^-9) = 1.66*10^8, or 166Mhz, that's what it's rated to run...if you find say 16 chips that run at 200mhz and pop em on some PCB you can sell those as PC3200...it's still 6ns chips though because that's what JEDEC said those chips had to be rated at...even though they run at 5ns.

Not the most clear explanation but i hope it helps.

Currently (Mar 2003), most modules are using 32Mx8 = 256 Mb DRAM chips, regardless of speed (6ns, 5 ns or 4.5 ns).

Each 256 Mb DRAM chip is organized as 32Mx8. There are 8 bit I/O per chip. 8 DRAM chips form a bank. A module with one bank or two banks has 64 bit I/O (8 Bytes).


For current AMD MB, maxMemoryBandwidth = fsb x 2 x 8 MB/s

x 2 is because of DDR (double data rate), i.e. data are transferred at both the rising and falling edge of the memroy clock

x 8 is because there are 8 bytes or 64 bits transferred at each cycle

E.g. at fsb = 166 MHz, maxMemoryBandwidth = 166 x 2 x 8 = 2656 MB/s (called PC2700)

at fsb = 200 MHz, maxMemoryBandwidth = 200 x 2 x 8 = 3200 (called PC3200)


For Intel P4, the fsb is quad rate, i.e. the fsb is running TWICE as fast as the memory bus speed at DDR.

maxMemoryBandwidth = fsb x 4 x 8 MB/s

E.g. at fsb = 166 * 2
memory bus = 166 (DDR 333, PC2700)
maxFSBandwidth = 166 x 4 x 8 = 5312 MB/s
Dual channel, memory module bandwidth = 2 x 2656 = 5312 MB/s
(but there is an overhead in running dual channel, eff BW ~ 4000 MB/s)

shortyes said:

...

aka 6ns chips how high will these go?

Reason Crucial has 6ns rated at pc2700 while kingston is using 6ns on pc3200

Click to expand...

The memory modules that use 6 ns DRAM chip and labelled as PC3200 are overclocked memory modules. The manufacturer sorts and selects the faster chip among the 6 ns DRAM chips, and claim them to run as 5ns modules (200 MHz clock).