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OC ram question

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Felony44

Registered
Joined
Jan 2, 2010
I have a Gigabyte MA785G-UD3H MB and I was looking at adding ram. I know alittle about overclocking and noticed the MB box says "DDR2 1333+" How can I achieve this? 800, or 1066.

Reading the manual it says it Note: Due to AMD AM3/ AM2+ CPU limitation, memory module DDR2 1066 or above speed is only supported by 1 dimm per channel.

I asume that means if I buy 1066 ram I am limted to 4gb if its a 2gb dimm??? correct?

I have corsairs xms2 TWIN2X2048-6400C4 800

What Im looking for is more speed

CPU AMD phenom 965 black
Video Asus Engtx275
 

vgta88

Member
Joined
Nov 15, 2007
these boards are dual channel so each pair of dimms is a channel. for speeds above 1066 you can only use 1 dimm per channel x2. meaning you can only use 2 sticks of ddr2 1333+ one on each channel.

i think ddr3 boards are 3 channel.(intel)
 

Dooms101

Member
Joined
Dec 28, 2009
Location
under a heatsink
DDR2-1333+ generally only means that the board has the capability of running also capable ram those speeds by OC'ing the system bus. But, it might actually have a ram divider for running at that speed as an option (although I doubt it does.)
Here's a little chart for ram dividers:

Ram frequency = (system bus divided by (ram ratio)) multiplied by 2

1:1 | DDR2- 400mhz | (200mhz / (2 / 1))
3:4 | DDR2- 533mhz | (200mhz / (3 / 4))
3:5 | DDR2- 667mhz | (200mhz / (3 / 5))
1:2 | DDR2- 800Mhz | (200mhz / (1 / 2))
3:8 | DDR2-1066mhz | (200mhz / (3 / 8))
1:3 | DDR2-1200mhz | (200mhz / (1 / 3))
3:10| DDR2-1333mhz | (200mhz / (3 / 10))


Those are all the ratios for common DDR2 (except 1333mhz... I've never seen stock DDR2-1333mhz before....) However, if you're BIOS only has options for 1066mhz (which most do) or 3:8 ratio, then you'll have to OC the system bus to get higher speeds. Here's a table demonstrating some values:

____|__200mhz_|__205mhz_|__210mhz_|__215mhz_|_220 mhz_|__225mhz_|__230mhz_|__235mhz_|__240mhz_|_245 mhz_|__250mhz_|__255mhz_|__260mhz_|

1:2 | 0800mhz | 0820mhz | 0840mhz | 0860mhz | 0880mhz | 0900mhz | 0920mhz | 0940mhz | 0960mhz | 0980mhz | 1000mhz | 1020mhz | 1040mhz |
3:8 | 1066mhz | 1093mhz | 1120mhz | 1147mhz | 1173mhz | 1200mhz | 1227mhz | 1253mhz | 1280mhz | 1306mhz | 1333mhz | 1360mhz | 1386mhz |
1:3 | 1200mhz | 1230mhz | 1260mhz | 1290mhz | 1320mhz | 1350mhz | 1380mhz | 1410mhz | 1440mhz | 1470mhz | 1500mhz | 1530mhz | 1560mhz |


This table shows different OC possibilities for different ram ratios. The values in red are => 1333mhz. If you do plan on getting a super high OC, buy ram that can handle it. Generally you want to be in a 150mhz range from your target and stock speeds. So if you want to hit DDR2-1120mhz, get some good DDR2-1066mhz or DDR2-1100mhz, or DDR2-1200mhz. As for you channels question, you would have to place 1 DIMM (or stick) in each channel. So your 4 slots are seperated into 2 channels, the 1st + 2nd = 1st channel, and 3rd and 4th = 2nd; or 1st and 3rd = 1st channel and 2nd and 4th = 2nd channel. These names can be independent from physical order as well. So you'll have to look it up for your board. You'll have to place 1 DIMM in each of the first slot of each channel.

Also keep in mind that cas latency has alot to do with performance too, and for every drop in cas latency you're effectively becoming equivelent to the next speed above yours with your cas latency + 1. Example:

DDR2-800mhz (4-4-4-12) ~= DDR2-1066mhz (5-5-5-15) ~= DDR2-1200mhz (6-6-6-18)

This is why when OC'ing, say a 2x2gb DDR2-800mhz (5-5-5-15) kit; you have to consider cas latency.
Becuase if you can get the kit running at DDR2-760mhz (253mhz / (2 / 3)) with 4 cas latency, and also DDR2-900mhz (225mhz / (1 / 2)) with 5 cas latency, the first choice is most likely higher performing. But running benchmarks is always the best for testing performance.

Hope this helped!
 
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