HT or HyperTransport.
Not firmiliar with the Abit BIOS
HT, HTT, somewhat confusing.
The HT can refer to a multiplyer or 5x,4x,3x,or 2x and how it maintains the RAMs speed relative to the CPU's HTT (once known as FSB or front side bus).
Default = 5x 200MHz =1000 when OCing the CPU the RAM's HT must be lowered to maintain a 1000MHz total or less to keep the RAM stable, so ...Use 4x for 201-250
3x for 251-333.
Take a peek at this utility and you will see the corelation.http://math.gogar.com/athlon64.cgi
A basic from Gogars
(HTT) 250MHz x 11 (CPU multiplyer) = 2750
(HTT) 250MHz x 5 (RAM HT) = 1250 <<< BAD 250MHZ beyond the 1000MHZ limitSo the RAM's HT must be reduced to 4x for up to an HTT of 250
So with the RAM at default DDR400 it will actually be running DDR500 speeds with the above settings.