Why do some of the Tyan bios versions allow the user to change some memory values?
The default value comes from the memory SPD and not from the system BIOS. However some memory vendors have set aggressive values in the SPD and it will cause system errors or system instablity. The Tyan BIOS has provided a manual way to set all the clock timing inside setup to offer an alternative for setting this value. The officiallysupported memory listings do not need to have any alterations to memory timings to operate correctly.