Options : Enabled, Disabled

This BIOS feature enables or disables the AGP2X transfer protocol. The standard AGP1X only makes use of the rising edge of the AGP signal for data transfer. At 66MHz, this translates into a bandwidth of 264MB/s. Enabling AGP 2X Mode doubles that bandwidth by transferring data on both the rising and falling edges of the signal. Therefore, while the clockspeed of the AGP bus still remains as 66MHz, the effective bandwidth of the bus is doubled. This is the same method by which UltraDMA 33 derives its performance boost.

However, both the motherboard chipset and the graphics card must support AGP2X transfers before you can use the AGP2X transfer protocol. If your graphics card support AGP2X transfers, enable AGP 2X Mode for a higher AGP transfer rate. Disable it only if you are facing stability issues (especially with Super Socket 7 motherboards) or if you intend to overclock the AGP bus beyond 75MHz and can't just disable sidebanding.

AGP Master 1WS Read

Options : Enabled, Disabled

By default, the AGP busmastering device waits for at least 2 wait states or AGP clock cycles before it starts a read transaction. This BIOS option allows you to reduce the delay to only 1 wait state or clock cycle. For better AGP read performance, enable this option but disable it if you experience weird graphical anomalies like wireframe effects and pixel artifacts after enabling this option.

AGP Master 1WS Write

Options :  Enabled, Disabled

By default, the AGP busmastering device waits for at least 2 wait states or AGP clock cycles before it starts a write transaction. This BIOS option allows you to reduce the delay to only 1 wait state or clock cycle. For better AGP write performance, enable this option but disable it if you experience weird graphical anomalies like wireframe effects and pixel artifacts after enabling this option.

USWC Write Posting

Options : Enabled, Disabled

USWC or Uncacheable Speculative Write Combination improves performance for Pentium Pro systems (and possibly other P6 processors as well) with graphic cards that have a linear framebuffer (all new ones do). By combining smaller data writes into 64-bit writes, it reduces the number of transactions required for a particular amount of data to be transferred into the linear framebuffer of the graphics card.

However, it may cause issues like graphic corruption, crashes, booting problems, etc... if the graphics card does not support such a feature.

In addition, tests using FastVid (in the old article - The Phoenix Project) have shown that such a setting can possibly decrease performance, instead of increasing it! This was observed with the Intel 440BX-based motherboard.

So, if you are using a Pentium Pro processor or a motherboard based on older chipsets, enable it for faster graphics performance. If you own a newer motherboard, you can try enabling it but make sure you run some tests to determine if this feature really improves performance or not. It's quite possible that it may not anything at all or even decrease performance.

Spread Spectrum

Options : Enabled, Disabled, 0.25%, 0.5%, Smart Clock

When the motherboard's clock generator pulses, the extreme values (spikes) of the pulses creates EMI (Electromagnetic Interference). The Spead Spectrum function reduces the EMI generated by modulating the pulses so that the spikes of the pulses are reduced to flatter curves. It does so by varying the frequency so that it doesn't use any particular frequency for more than a moment. This reduces interference problems with other electronics in the area.

However, while enabling Spread Spectrum decreases EMI, system stability and performance may be slightly compromised. This may be especially true with timing-critical devices like clock-sensitive SCSI devices.

Some BIOSes offer a Smart Clock option. Instead of modulating the frequency of the pulses over time, Smart Clock turns off the AGP, PCI and SDRAM clock signals when not in use. Thus, EMI can be reduced without compromising system stability. As a bonus, using Smart Clock can also help reduce power consumption.

If you do not have any EMI problem, leave the setting at Disabled for optimal system stability and performance. But if you are plagued by EMI, use the Smart Clock setting if possible and settle for Enabled or one of the two other values if Smart Clock is not available. The percentage values denote the amount of jitter (variation) that the BIOS performs on the clock frequency. So, a lower value (0.25%) is comparatively better for system stability while a higher value (0.5%) is better for EMI reduction.

Remember to disable Spread Spectrum if you are overclocking because even a 0.25% jitter can introduce a temporary boost in clockspeed of 25MHz (with a 1GHz CPU) which may just cause your overclocked processor to lock up. Or at least use the Smart Clock setting as that doesn't involve any modulation of the frequency.

Auto Detect DIMM/PCI Clk

Options : Enabled, Disabled

This function is similar to the Smart Clock option of the Spread Spectrum function. The BIOS monitors the AGP, PCI and SDRAM's activity. If there are no cards in those slots, the BIOS turns off the appropriate AGP, PCI or SDRAM clock signals. And when there's no activity in occupied AGP / PCI / SDRAM slots, the BIOS turns off those clock signals as well.

This way, EMI (Electromagnetic Interference) can be reduced without compromising system stability. This also allows the computer to reduce power consumption because only components that are running will use power.

Still, if you do not have any EMI problem, leave the setting at Disabled for optimal system stability and performance. Enable it only if you are plagued by EMI or if you want to save more power.