On 30 Jul 2007 at 14:33, Jim Leonard wrote: > I've never heard of this. Are you talking about monitoring a bit in > the 8253? -- Jim Leonard (trixter at oldskool.org) Bit 4, port 61h. You can use a simple toggle test to see if it's there, but on just about every system I've ever seen, it is. One of the holdovers from the PC-AT architecture. Cheers, Chuck