Slow Operation of PC Cards in Windows NT4
The P-Series driver has built in detection logic that detects a poorly written IRQ handler for a PC-Card that would normally crash the PC. When a "Dirty IRQ Handler" is detected, the IRQ is disabled and handled by polling on a timer tick, so transfer performance may be poor, however the PC does not crash as it would without the P-series driver.
The Microsoft Windows NT4 ATA driver (ATDISK.SYS) is one such "Dirty IRQ Handler" driver, and for this reason the P-Series driver is set up in Windows NT4 to enable polled mode for best transfer performance without crashing the PC.
Sometimes, the PC-Card hardware associated with a correctly written "Clean IRQ Handler ;-)" driver may defeat the "Dirty IRQ Handler" detection logic and it may go to polled mode. In this case, try this registry setting. If your PC-Card's performance is even worse, then revert back to the old setting with this registry setting; your card has a "Dirty IRQ Handler" and the only solution is to contact your PC-Card vendor for a driver update for their PC-Card.
NOTE: The above settings can be made in Windows 2000 and Windows NT4 operating systems. Do not use them in Windows9x or WindowsMe.
Further information for developers:
It is recommended that device driver writers should write their IRQ handlers for their PC-Cards using Microsoft's current recommended guidelines in the Windows NT/2000 DDK for PCI devices that are capable of sharing an IRQ. See the Microsoft Windows NT/2000 DDK for more information.