February 19th, 2018

This is a race the display driver wouldn’t normally expect to lose

Raymond Chen
Raymond Chen

One of my colleagues from the Windows 95 project reminded me of a problem that I was called to debug. If the floppy drive was in use, the display driver was more likely to crash.

It wound up being a race condition between the floppy driver and the display driver. This is a race the display driver wouldn’t normally expect to lose.

The problem occurred on machines running the kernel debugger. When the kernel debugger was connected, the display driver printed diagnostic information, which was sent over the serial port, which slowed down the display driver and made it more likely that the floppy drive would interrupt it at a bad time.

Category
Old New Thing
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History

Author

Raymond Chen

Raymond has been involved in the evolution of Windows for more than 30 years. In 2003, he began a Web site known as The Old New Thing which has grown in popularity far beyond his wildest imagination, a development which still gives him the heebie-jeebies. The Web site spawned a book, coincidentally also titled The Old New Thing (Addison Wesley 2007). He occasionally appears on the Windows Dev Docs Twitter account to tell stories which convey no useful information.

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