NVIDIA nForce 590 SLI Technology Chipset Overclocking
DU-02451-001_v01
19
05/17/06
DDR2 Memory Interface Overclocking
Because so much of the memory controller settings can be tuned and because
memory speeds depend on the CPU HTT reference clock and CPU multiplier,
overclocking memory is complicated.
The two approaches to overclocking memory are to:
Increase memory bandwidth by increasing frequency
Decrease memory latency which may lead to frequency reductions
Since different memory devices exhibit different overclocking limitations, some are
more suited for higher frequency while others are best for achieving low CAS
latency. Because this memory device used with the nForce 590 provides higher
performance with increased memory frequency than with reduced latency, this
document focuses on techniques to increase memory bandwidth using Corsair
TWIN2X2048-8500C5 with Enhanced Performance Profiles (EPP) technology.
Rule of Thumb:
To decide which approach to overclocking memory works better
for your memory device, calculate the reduction of CAS latency
when the memory is overclocked and divide that value by the
operating memory frequency. The smaller the value, the higher
the throughput and performance will be.
Your two basic options are a faster clock with longer CAS latency
(like
t
CL
= 5) or a slower clock with shorter latency (like
t
CL
= 4).
For example, 5 ÷ CLK1 might be smaller than 4 ÷ CLK2. The
settings with the smallest result will likely provide better
performance, you would choose CLK and
t
CL
= 5.
The AM2 processor’s memory controller architecture is such that the effective
memory frequency is a function of the CPU’s frequency and an internal memory
clock divider. The CPU frequency is also a function of CPU reference clock, or
CPU HyperTransport reference clock, as well as the CPU multiplier. The
relationships are as follows:
Memory frequency = CPU frequency (MHz) ÷ internal integer clock divider
CPU core frequency = CPU reference clock (MHz)
×
CPU multiplier
A built-in memory clock divider lookup table is used to calculate the memory
frequency. The divider varies based on the memory timings selected (200 MHz, 533
MHz, 667 MHz, and 800 MHz). It increases as the CPU multiplier increase. For
DDR-800 memory setting with an even-numbered CPU multiplier of 10 or above, it
is easy to calculate the memory frequency without knowing what the internal clock
divider is. Multiply 800 MHz by the increase in CPU reference clock with respect to
200 MHz:
Memory frequency = 800 MHz
×
CPU reference clock ÷ 200 MHz
Before you proceed to overclock the CPU core clock, eliminate all other sources of
system instability.
