Overclocking with Q9450 & DDR3

[Lefti]

Hi

I am in the process of purchasing a new system with overclocking in mind.

I intend to use a Q9450 CPU with a Gigabyte GA-X48T-DQ6 Mobo.

The question is memory, i was going to go with 4gb (2X2048MB) of OCZ Reaper DDR3 RAM, it comes in 3 flavours.

DDR3-1333Mhz 6-6-6-18 ~£135

DDR3-1600Mhz 7-7-7-24 ~£165

DDR3-1800Mhz 8-8-8-27 ~£173

Originally i was going to go for the 1333Mhz variety however after reading a certain overclocking guide on these forums i am not so confident any more. Most of what i have read focusses on using DDR2 not DDR3.

The Q9450 uses 8 x 333Mhz = 2.66GHz at stock settings.

I read that with DDR2 you divide the rated speed by 2 and for DDR3 you divide the rated speed by 4:

so 1333Mhz / 4 = 333Mhz for the RAM

the CPU FSB is running at 333Mhz

Does this mean if i choose the DDR3-1333Mhz RAM then i have no room for overclocking, without overclocking the RAM also ?

 

[bpogdowz]

Nah u can still over clock but you have to run the RAM at less than the rated speed by applying a 5:4 or 3:2 ratio. The RAM might over clock some but the RAM makers usually optimize the BIOS of the RAM so it will not over clock to 1600, 1800, 2000 with the same voltage as the models made that way ( they want you to buy the faster model). Also the 1333 models don't have the appropriate heat sync to handle such manual over volts. The architecture on 1333 models might not be designed the same either.

 

[Mondoman]

No, sorry, either the guide or your interpretation of it is very confused. You can certainly overclock with DDR3, but at this point there's not much point to getting DDR3 since DDR2-800 can handle a FSB speed up to 1600MHz.

 

[Lefti]

Thanks for the posts,

I understanding is certainly confused at this point

I found the guide that confused me, this is the quote from Graysky's post, which is sticked somehwere above:

• The first part is self-explanatory (DDR3 memory).
• The number after it is the data transfer rate. Simply divide it by 4 to get the maximum FSB speed for which the module is rated. Example: 1600/4 = 400 MHz. Therefore, DDR3-1600 can work on systems with a FSB of up to 400 MHz (anything more and you’re lucky).
• The PC3-XXXXX is designation denoting theoretical bandwidth in MB/s. Some memory manufactures use this instead of the DDR3-xxxx designation. You can calculate it for any FSB you want by simply taking the FSB and multiplying by 32 (rounded in some cases). Example using a 400 MHz FSB: 400x32=12800. So you’d need at least PC3-12800 to run on FSB of 400 MHz.

This lead me to believe that DDR3-1333 is rated for a FSB of 333MHz, would i be right in thinking i could use the dividers to increase the FSB speed beyond 333MHz ?

Lefti

 

[bpogdowz]

The FSB is bus speed times 4.

 

[Mondoman]

The problem is that the wording is confusing. What you are trying to do is to match the memory bus throughput with the FSB throughput (the famed 1:1 ratio). Assuming you are running 2 or 4 DIMMs in dual-channel mode, then the memory bus throughput will be the memory bus speed x 2. The FSB throughput is the FSB clock x 4. Thus, if you are running your FSB at 400MHz clock, you want to match its throughput (400 x 4 = 1600MHz) with the memory bus throughput. DDR2-800 memory bus speed x 2 for dual-channel mode = 1600MHz throughput, matching the FSB throughput. Similarly, DDR3-800 memory bus speed x 2 for dual-channel mode = 1600MHz throughput, matching a 1600MHz FSB throughput. If you are running a faster FSB, you will need to run your memory faster than in the above examples.