Data Acq slower in XP vs 98

Data acquisition app written in VB6 on a Win98 machine. I get data at 1 to 2 millisecond intervals. I could go faster, but I am using the multimedia timer to get system time rather than using the clock on the interface card. Sometimes I need those rates for long periods of time.

Transferring that executable to an XP machine, and the fastest I can get is about 15 ms intervals. Same PCI-bus data acquisition card and driver library.

Is the system overhead for XP that much greater, even accounting for the fact that the computer is 3-4 times faster CPU and motherboard?

 

It should not be.

Without seeing the code I can't be sure but a major difference between the DOS/9X/ME systems and the NT systems is how they handle applications making hardware calls.

NT will not allow it. There is a program/utility/layer called HAL (hardware abstration layer) that intercepts all hardware calls, checks them for safety, and then makes what HAL sees as that call in a manner that isn't likely to crash the system.

It added lots to system stability but we found that lots of apps worked strangely or no longer worked. Mostly older games where a clever programmer had done tricks to make the hardware and OS do things it otherwise could not do. Some calls no longer worked at all. Some did strange things when HAL mis-interpreted.

It may not be a HAL issue but it certainly could be. Otherwise I'd expect XP to be faster than 9X.

 

Which timer?

I found that the multimedia timer function timeGetTime as a part of winmm.dll for the Win98 system only ticks every 15 milliseconds in XP. I could get true (sort of) millisecond timing with that in Win98. Is there an equivalent API function that I can read to the nearest millisecond in XP? Or is there another way to get to the system clock at millisecond intervals?