Vista sees DDR2 800 as 400

[AAArDvArK]

All my hardware under Vista gets a rating of 5.3 and above, except my meory which gets a 4.5, since the RAM is DDR2 XMS 800mhz I thought it strange and ran CPU-Z.

Sure enough under the memory tab timing frequency is 400.0 MHz

I checked the BIOS and the memory multiplier is set to auto and a reading of 800 is shown. so thats ok.



WTF?

Apreciate any insight.


Update: clocked down the speed from BIOS to 667 through the memory multiplier and CPU-Z under Vista reads 333.3.

 

[monst0r]

um.. you realize this is ddr ram (double data rate). the number your seeing is one signal (correct me if im wrong) ddr ram sends data on the up and down signals, thus doubling the data being sent. the frequency your seeing is perfectly fine and normal

 

[AAArDvArK]

D'OH!

Thank you. I did not know that memory frequency was calculated that way.

 

[misiu_mp]

Actually the frequency of DDR 400 and DDRII 800 is 200MHz in both cases.
As mentioned, both the raising and the falling edge of the signal is used for transmission so the effective frequency is 400MHz.
DDRII uses an extra trick that allowes it to fetch twice during each cycle (i think it is some kind of pre-fetching). This makes it almost look like further doubling the frequency, Hence the name DDRII 800. This technology have an intrinsic penalty of added latency. Thats why DDR comes with cl 2-3 and DDRII with cl4-6.
While saying that DDR have effectively doubled the frequency (from 200 to 400) is justified, it is debatable whether the DDRII trick can be called doubling the frequency (because the mechanism of memory acces is changed as well as latency increased).
The coming DDRIII will be exactly like DDRII but will be fetching 4 pieces in one cycle (looking like 200x2x4 = 1600MHz) and the latency will be even more increased (i guess cl6-9),

 

[monst0r]

oh yea, i forgot that ddr2 was a different design...=p
anyway,
your welcome aaardvark 😀

Actually the frequency of DDR 400 and DDRII 800 is 200MHz in both cases.
As mentioned, both the raising and the falling edge of the signal is used for transmission so the effective frequency is 400MHz.
DDRII uses an extra trick that allowes it to fetch twice during each cycle (i think it is some kind of pre-fetching). This makes it almost look like further doubling the frequency, Hence the name DDRII 800. This technology have an intrinsic penalty of added latency. Thats why DDR comes with cl 2-3 and DDRII with cl4-6.
While saying that DDR have effectively doubled the frequency (from 200 to 400) is justified, it is debatable whether the DDRII trick can be called doubling the frequency (because the mechanism of memory acces is changed as well as latency increased).
The coming DDRIII will be exactly like DDRII but will be fetching 4 pieces in one cycle (looking like 200x2x4 = 1600MHz) and the latency will be even more increased (i guess cl6-9),

^listen to this guy

 

[Mondoman]

Actually the frequency of DDR 400 and DDRII 800 is 200MHz in both cases.

To clarify, the frequency of the *memory bus* is 200MHz for DDR-400 and 400MHz for DDR2-800.

...
DDRII uses an extra trick that allowes it to fetch twice during each cycle

Internally to the DIMM, DDR2 combines two parallel streams of data into one, thus doubling the data rate (internally), and adding a bit more latency. However, remember that a 3-cycle latency at DDR-400 speed is the same absolute amount of time as a 6-cycle latency at DDR2-800 speed.

 

[misiu_mp]

Actually the frequency of DDR 400 and DDRII 800 is 200MHz in both cases.

To clarify, the frequency of the *memory bus* is 200MHz for DDR-400 and 400MHz for DDR2-800.

...
DDRII uses an extra trick that allowes it to fetch twice during each cycle

Internally to the DIMM, DDR2 combines two parallel streams of data into one, thus doubling the data rate (internally), and adding a bit more latency. However, remember that a 3-cycle latency at DDR-400 speed is the same absolute amount of time as a 6-cycle latency at DDR2-800 speed.

Yes. The internal (core) frequency of both types is the same (200Mhz in case of DDR400/DDRII800). The external (bus) frequency is doubled in DDRII in order to accomodate the doubled amount of data fetched from the core (at the same bus width). Since latencies depend on the speed of the core they are the same in both cases, but measured in bus cycles will be at least doubled in DDRII.
That means that DDR400 runs at bus and core clock of 200Mhz, while DDRII400 will have the core clock reduced to 100Mhz, decreasing the costs and (slightly) performance due to latencies.