So I finally got a new machine at work - being a Dell P4 with HTT on it. As I normally use SMP machines I thought I would have a goat getting this running. Running the box with an SMP kernel but machdep.hlt_logical_cpus set to "1" works fine. Seem rock solid and stable, but all processes are running on logical CPU 0. Altering machdep.hlt_logical_cpus to be "0" and I get what I would expect - a mix of processes running on CPU's 0 and 1. But if I try and do any large compiles (e.g. a make buildkernel) then random processes die with signal 11. I would usually associate this with bad memory, but it only happens when I am running HTT. Had anybody else expereinced anything similar ? -pcf.