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BIOS and Overclocking

790i Ultra SLI Motherboards Compared

BIOS Frequency and Voltage settings (for overclocking)
FSB Clock 100 to 999 MHz (1 MHz)
Clock Multiplier Adjustment Yes
DRAM Linked Ratios Automatic, 1:1, 5:4, 3:2
DRAM Unlinked Data Rate DDR3-400 to DDR3-2500
PCIe Clock 100 to 200 MHz (1 MHz)
CPU Vcore 0.81875 to 2.42 Volts (0.00625 Volts)
CPU FSB Voltage 1.20 to 1.95 Volts (0.05 Volts)
Northbridge (SPP) 1.202 to 2.054 Volts (50 increments)
Southbridge (MCP) 1.50 to 1.85 Volts (0.05 Volts)
DRAM Voltage 1.418 - 2.810 Volts (59 increments)
CAS Latency Range tCAS: 5-18; tRCD: 1-15; tRP: 1-15; tRAS: 1-63

A full set of BIOS adjustments provides a broad enough range to support the extreme voltages used in liquid nitrogen cooled systems, as well as less-elaborate configurations. DRAM linked ratios are, however, subject to the same restrictions typical of Nvidia chipset LGA775 motherboards. Several linked ratios that are not manually selectable will appear via automatic configuration when various memory types are used with different CPU front side bus speeds.

Two CPU core voltage settings result in a single voltage, since one setting is simply a multiplier for the other. A line beneath the two shows the target result, so users no longer need a calculator to figure this out.

Like most recent high-end motherboards, the 790i Ultra SLI mystery motherboard has GTL Reference settings for four cores, which are best left to extreme tuners to figure out. Changes here often allow a lower CPU Core Voltage to provide a similar overclock, allowing tuners to shoot for higher speeds after the CPU has reached its voltage limit.

DRAM Reference Voltage is also separately tunable for each slot. Memory timing controls are complete, with a wide enough range to allow optimal performance at nearly any appropriate DDR3 speed.

Eight custom BIOS settings can be stored for later use, a feature that comes in very handy whenever a failed overclock attempt has forced the use of the CLR_CMOS button.

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