Before you start getting a headache just by looking at the title above and trying to visualize how in the world can memory be SLI ready, let us break this down for you. SLI-Ready memory modules is a term that the clever marketing people at NVIDIA have coined for their excellent implementation of a new memory profile type called Enhanced Performance Profile, or EPP for short. EPP is an extension to the existing JEDEC SPD specifications and is actually programmed into the DIMM EEPROMs. Memory modules that carry these EPP codes will have more advanced timing and performance information stored than the basic SPD timings.
So how does EPP actually work? Every DIMM module today has its own 256Byte EEPROM (Electrically-Erasable Programmable Read-Only Memory) where the SPD information is stored. However, the SPD only takes up the first 98Bytes leaving Bytes 99-256 literally free to be used. What NVIDIA has introduced is a new EPP profile that stores advanced timings including voltage, frequency and signal strength information that is more essential to overclocking and pushing the particular DIMM to its limits. EPP utilizes Bytes 99 to 127 of the EEPROM and comes in either a 'Full Performance' profile or 'Abbreviated Performance' profile. We will not go into too much detail on the actual profiles though the technically inclined can view the two different profile maps below for more information on what EPP stores in the EEPROM.
Just like how current motherboards detect and apply optimal SPD timings today, an nForce 590 SLI motherboard can detect and apply these advanced EPP timings to provide higher memory performance. Note that EPP does not only tweak memory timing parameters, but is an actual overclocking profile. When the nForce 590 SLI BIOS detects EPP settings, it will try to tweak the system according to options that have been selected by the user. As such, the SLI-Ready option can be disabled in the BIOS if users do not want to utilize the extended EPP functions. The following settings are available for SLI-Ready memory functionality.
CPU MAX – This option will tell the BIOS to try and match the EPP specifications through overclocking of the memory controller, HT link and CPU as well. This is most useful if you are using DIMM modules that are of higher frequency than the base FSB and you need to overclock the CPU to match with the memory speeds. Reading the EPP parameters off the DIMM, the nForce 590 SLI will be able to detect the maximum overclock capable for the particular DIMM. Depending on the EPP profile selected, the BIOS will then try its best to match the EPP profile in terms of timing and frequency. Of course, any overclocker will know that overclocking is a fickle art. No two hardware components are alike and your overclocking mileage may vary.
CPUOC 0% - As the options suggests, setting it to this option will tell the BIOS to try and increase memory performance while keeping the CPU at stock stock speeds. This is the safest option to use and will only prompt the BIOS to perform memory controller overclocking. The images below show a set of Corsair EPP DDR2-800 DIMMs used. With SLI-Ready Memory enabled and set to CPUOC 0%, the BIOS was able to overclock the memory to from 800MHz @ 12-4-4-4 to 932MHz @ 15-5-5-5. While the CPU is kept at about stock speeds, this parameter still fiddles with the CPU multiplier and HTT link speeds to achieve the higher memory overclock, but tries to keep the CPU clock within limits.
Other settings include CPUOC from 1%-6%, though the most impressive modes are the two described simply because of what the BIOS tries to do. This isn't your typical automatic overclocking which you see in many of today's motherboards. With EPP profiles and and SLI-Ready Memory BIOS, the nForce 590 SLI performs overclocking as close to what is possible through manual means, it is almost human and the level of intelligence is a little scary. This function just opens up care-free overclocking for many who want to achieve the best possible performance, but not necessarily the time to tweak.
Being NVIDIA's partner for SLI-Ready Memory, Corsair will be launching two 2GB DDR2 kits carrying the EPP profiles: TWIN2X2048-6400C4 800MHz low-latency DIMMs and the TWIN2X2048-8500C5 high-frequency 1066MHz DIMMs. As this article is being written, OCZ Technology has also announced that they will be jumping onto the SLI-Ready Memory bandwagon with a line of EPP memory modules as well.
We can really see EPP type DIMMs taking off in the future and while the nForce 590 SLI again benefits from this SLI-Ready Memory function, there is no stopping of any other chipset or manufacturer to program a BIOS to take advantage of the EPP profiles. Also if you happen to purchase EPP DIMMs in the future, you'd be rest assured that the piece of memory has a high overclocking potential, even if you do not have an SLI-Ready Memory capable motherboard or BIOS. Nifty features, but they all come at a cost that's more than the usual as well.