533 MHz RAM working at 266 MHz!!!!!!!!!!!!!!!!!!!!!!!

[gam0reily]

i have two DDR2 RAMs at 533 MHz (512 Mb + 512 MB = 1GB).
But when I check my RAM clocks with ClockGen, It only shows one of the RAM's clocks, that too at 266 MHz.!!!

i wanna know, are both of the RAMs shown on ClockGen?? If they are, then is there something wrong with my other RAM??

Also, if they are at 533 MHz speed, then why are they being shown at 266 MHz ???
Is it normal??

 

[mathew7]

It's ok. ClockGen always show the memory clock (to which all the CAS, RAS latencies/timings are referenced). But once it's time for the data to pe placed on the bus, an I/O clock is derived, which is 2x memoy clock for DDR2 and 4x memory clock for DDR3. So both frequencies "exist" on your memories. Check the table from the DDR2 wikipedia page.
Update: the clocks are common for all memory modules. That's why if you add a slower module, you will run the old ones at reduced speed.

 

[iam2thecrowe]

its DDR, so 266x2 (double data rate) gives an effective 533mhz. Its running like its supposed to, no need to worry.

 

[gam0reily]

its DDR, so 266x2 (double data rate) gives an effective 533mhz. Its running like its supposed to, no need to worry.

So if I even had a 1600 MHz DDR3 RAM, so then Clockgen would be showing 533MHz??

And also I mainly wanted to ask that why my other RAM is not being mentioned by it??

 

[mathew7]

its DDR, so 266x2 (double data rate) gives an effective 533mhz. Its running like its supposed to, no need to worry.

It's DDR2. And the 266x2 you mention for DDR(1) is not a clock by itself. That is "measured" in MT/s (as in Mtransactions)

So if I even had a 1600 MHz DDR3 RAM, so then Clockgen would be showing 533MHz??

Nope, it would show 200MHz. But the DDR3-1600 is NOT 1600MHz. It's 200MHz memory clock, 800MHz (x4) I/O clock and 1600MT/s (there are 2 transactions/IOclock). Just check wikipedia.

And also I mainly wanted to ask that why my other RAM is not being mentioned by it??

The clock is common to all modules. If you have 4 modules, they receive the same clock.

PS: Just made a search for DDR3 1600MHz, and specs I see are all DDR3-1600, even mentioned as PC3-12800. These are NOT 1600MHz. This is the lack of technical knowledge from marketing staff and "bigger numbers are better" strategy.

 

[gam0reily]

It's DDR2. And the 266x2 you mention for DDR(1) is not a clock by itself. That is "measured" in MT/s (as in Mtransactions)

Nope, it would show 200MHz. But the DDR3-1600 is NOT 1600MHz. It's 200MHz memory clock, 800MHz (x4) I/O clock and 1600MT/s (there are 2 transactions/IOclock). Just check wikipedia.

The clock is common to all modules. If you have 4 modules, they receive the same clock.

PS: Just made a search for DDR3 1600MHz, and specs I see are all DDR3-1600, even mentioned as PC3-12800. These are NOT 1600MHz. This is the lack of technical knowledge from marketing staff and "bigger numbers are better" strategy.

few points to get cleared --

-All I want to understand is that whether showing 266 MHz on my RAM is normal or not.
So, I believe you mean "yes".

-And now why would a 1600 MHz show 200 MHz when a 533 MHz is showing 266??

-yeah, I understand that all modules run at the same speed, reduced or not. So the Clockgen will only show one clock speed.

-What is DDR3 1600 not being 1600 MHz is about??

 

[gam0reily]

ok, so I did a little wiki on DDR3 and DDR2, and came up with the following -

1. the clock rates are not the one the stated by the company -
i.e., the clock speed is found out by dividing the module name by 64.

For eg- 1600 DDR3 has module name PC3-12800
so clock speed is 12800 / 64 = 200 MHz. So clear on that.

2. I believe what ClockGen is showing is I/O bus clock-

DDR3 - http://en.wikipedia.org/wiki/DDR3_SDRAM
DDR2 - http://en.wikipedia.org/wiki/DDR2_SDRAM

Clearly, it can be seen that I/O bus clock is exactly the half of data rate.

So if clock Gen shows I/O bus clock, then I have no problems whatsoever now.