mojo
07-29-2005, 01:29 AM
Finally, we are seeing people overclocking their components on GAMERS more than ever. This guide on overclocking Memory was promised a while ago, but IMO, the timing couldn't be better since we have members already overclocking Memory and confusing the younguns with all those numbers.
First of all, much like FSB on a CPU, the higher the speed (in MHz) that your memory is clocked at is a very good estimate of how high your memory performance. However, this is not the only number of concern when overclocking memory.
Here are some explanations for some of the other important memory parameters that should be considered to determine performance.
CAS - CAS latency is the number of clock cycles between the memory receiving a "read" command and actually starting to read.
RAS/Row Precharge or Row Address Strobe (Trp) - This Precharge to Active timing controls the length of the delay between the precharge and activation commands.
RAS-to-CAS Delay (Trcd) - This timing controls the length of the delay between when a memory bank is activated to when a read/write command is sent to that bank.
Row-active-delay (Tras) - The Active to Precharge timing controls how soon after activation the access cycle be started again.
CPC: This is the delay between when a IC is selected and the time commands can be issued to the IC. The more chips on a module (Single vs. double sided) the more difficult it is for the memory controller to do this in 1 command clock. Most quality modules with an A64 Processor can do 1T rates on 256 and 512mb modules. 2T can increase your overclock but at a substantial loss in bandwidth.
Typical Settings: 1T,2T
These timings might sound like nonsense to some of us, but just remember, the lower these values, the better the performance since there is less delay between cycles.
Also in order to get better timings, higher DIMM Volage is usually required.
Example of very good memory timings for PC 3200 RAM running @ 200MHZ (DDR 400):
CAS Latency: 2
RAS/Row Precharge (tRP): 2
RAS-to-CAS Delay (tRCD): 2
Row-active-delay (tRAS): 5
CPC: 1T
thus is usually written 2-2-2-5-1T
Recently, since the release of 90nm AMD Athlon 64 CPUs, It was realized that these CPUs could overclock to significantly higher fsb than 200MHz. Memory manufacturers have also introduced modules which are pre tested to guarantee that they will be stable @ uber high frequencies and uber lower latencies.
We have noticed that Corsair and G Skill are now using Samsung TCCD RAM chips in order to achieve speeds of 300MHz! with 2.5-4-4-8 @ 2.6-2.7V. This is quie good, but still does not take advantage of memory timing tweaks.
We have also seen Mushkin redline series and OCZ performance memory modules that can also clock @ decent speeds around 250MHz with 2-2-2-8 timings. To achieve these timings, often 3.3V is required. With this type of Voltage, TCCD just cries and says no. OCZ and Mushkin also have 300MHz modules which run @ similar timings to TCCD RAM based modules.
The million dollar question, which is more important? timings or MHz?
Well, I am not going to show u benchmarks that clarify this, instead I will simply say that:
1) Higher MHz gives your more MHz overclockability for your CPU.
2) At extremely high MHz, better timings are not yet possible and Memory performance is still around he same as lower MHz with better timings.
Hope you all enjoy this guide. Your input would be greatly appreciated.
*EDIT*
ADVANCED SETTINGS FOR AMD SOCKET 939 DUAL CHANNEL MEMORY
First of all, much like FSB on a CPU, the higher the speed (in MHz) that your memory is clocked at is a very good estimate of how high your memory performance. However, this is not the only number of concern when overclocking memory.
Here are some explanations for some of the other important memory parameters that should be considered to determine performance.
CAS - CAS latency is the number of clock cycles between the memory receiving a "read" command and actually starting to read.
RAS/Row Precharge or Row Address Strobe (Trp) - This Precharge to Active timing controls the length of the delay between the precharge and activation commands.
RAS-to-CAS Delay (Trcd) - This timing controls the length of the delay between when a memory bank is activated to when a read/write command is sent to that bank.
Row-active-delay (Tras) - The Active to Precharge timing controls how soon after activation the access cycle be started again.
CPC: This is the delay between when a IC is selected and the time commands can be issued to the IC. The more chips on a module (Single vs. double sided) the more difficult it is for the memory controller to do this in 1 command clock. Most quality modules with an A64 Processor can do 1T rates on 256 and 512mb modules. 2T can increase your overclock but at a substantial loss in bandwidth.
Typical Settings: 1T,2T
These timings might sound like nonsense to some of us, but just remember, the lower these values, the better the performance since there is less delay between cycles.
Also in order to get better timings, higher DIMM Volage is usually required.
Example of very good memory timings for PC 3200 RAM running @ 200MHZ (DDR 400):
CAS Latency: 2
RAS/Row Precharge (tRP): 2
RAS-to-CAS Delay (tRCD): 2
Row-active-delay (tRAS): 5
CPC: 1T
thus is usually written 2-2-2-5-1T
Recently, since the release of 90nm AMD Athlon 64 CPUs, It was realized that these CPUs could overclock to significantly higher fsb than 200MHz. Memory manufacturers have also introduced modules which are pre tested to guarantee that they will be stable @ uber high frequencies and uber lower latencies.
We have noticed that Corsair and G Skill are now using Samsung TCCD RAM chips in order to achieve speeds of 300MHz! with 2.5-4-4-8 @ 2.6-2.7V. This is quie good, but still does not take advantage of memory timing tweaks.
We have also seen Mushkin redline series and OCZ performance memory modules that can also clock @ decent speeds around 250MHz with 2-2-2-8 timings. To achieve these timings, often 3.3V is required. With this type of Voltage, TCCD just cries and says no. OCZ and Mushkin also have 300MHz modules which run @ similar timings to TCCD RAM based modules.
The million dollar question, which is more important? timings or MHz?
Well, I am not going to show u benchmarks that clarify this, instead I will simply say that:
1) Higher MHz gives your more MHz overclockability for your CPU.
2) At extremely high MHz, better timings are not yet possible and Memory performance is still around he same as lower MHz with better timings.
Hope you all enjoy this guide. Your input would be greatly appreciated.
*EDIT*
ADVANCED SETTINGS FOR AMD SOCKET 939 DUAL CHANNEL MEMORY