FSB:DRAM 1:5, BCKL 100Mhz, DRAM Freq: 665.1Mhz <<< Why don't they add up? >>>

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coffidu

Reputable
Aug 15, 2014
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4,510
Hello everybody,

I am very new to CPU / DDR clock speeds and I have never overclocked my system before.
I am only interested in understanding my system's specs (not overclocking), and I came across this conundrum.

My laptop has a:
CPU: i5-2450M
DDR3-1333 MHz

Cpu-z says my FSB:DRAM rate is 1:5, when my Bus Speed/BCKL is 100Mhz, and the DRAM frequency 665.1Mhz

I understand why my DRAM frequency is 665 (1333Mhz / 2) but why is the FSB:DRAM ration 1:5?

Question 1: What is downgrading my memory to run at 500Mhz (admittedly x2 from DDR, so 1,000Mhz), instead of the full 665 (or 1,333Mhz after accounting for DDR)? Is it a BIOS setting?

Question 2: Is a ratio of 1:5 more stable than 1:6.5 or 1:6?

Question 3: Does this mean that at the moment (with a 1:5 ratio) it doesn't really matter if I had a DDR3-1066 Mhz or DDR3-1333Mhz, because my memory would work at 1000Mhz anyway?

Question 4: It may be no surprise, but I am not using my laptop for processor intensive tasks, and the only benefit I am seeking from understanding and optimising my computer is the peace of mind that I am getting the most out of it (even if that fraction of a second less it takes it to handle my normal tasks is unnoticeable). The question being: Is it worth trying to get my memory to work at 1333Mhz (if indeed it isn't)? Stability, is of course critical (even if speed is not), as nobody likes their system to crash in the middle of heated game of Hearts.

Thank you kindly for your patience and help!

 
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ingtar33

ingtar33

Glorious
Dec 17, 2012
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no no no no... do not overclock your laptop.

as to your questions. ignore it. unless cpuid is showing your ram at any speed other then 1333, then it means nothing.

that old ratio thing is sorta a leftover of past overclocking nightmares. well frankly it was sorta fun to pull out a pen and paper and calculate how you're overclocking your system... but really it means basically nothing today.

 
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Pinhedd

Champion
Aug 7, 2007
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Hi,

Intel depreciated the FSB starting with the first generation Core i7 microprocessors. Ergo, there's no such thing as a FSB : DRAM ratio in newer computers because there's no FSB.

I believe that the DRAM clock is generated using a 133Mhz reference clock. A fractional PLL allows for nice increments of 33Mhz or clean increments of 133Mhz. This is more flexible than using the FSB as a reference. DDR3-1333 = 667Mhz; 667Mhz / 5 = 133Mhz (your PC). DDR3-1600 = 800Mhz; 800Mhz / 6 = 133Mhz (My laptop). I'll check my desktop later.
 
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coffidu

Reputable
Aug 15, 2014
2
0
4,510
Thank you both very much for your feedback. It's starting to make sense little by little.
I am not (and will not be) trying to overclock my laptop (not the least because I wouldn't know what I'd be doing - not fully in any case).
But it's very interesting to start learning about these things. Thank you, again!
 
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ingtar33

ingtar33

Glorious
Dec 17, 2012
9,019
199
45,840


back in the old school days of overclocking core2duos and core2quads it was a pretty important ratio... i don't remember all the vagueries, but it had to remain within certain standards depending on certain other settings... it was complicated and fun because you typically had to juggle 3 or 4 settings... every time to changed one setting's value you had to change 3 or 4 more settings just to make sure the computer would boot.

Nothing like overclocking today. Now days its so simple a child can do it.
 
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