At end of 1995, I wrote a Windows 95 application handling data from a data acquisition card ACL-8111! I had fun playing with the card and I bough the same for myself. I started writing a Linux driver and was very quickly able to handle direct IO access but also IRQ driven access.
To test it, I toke my soldering iron and made lot of sensor, captor and other digital circuits. I was able to digitize audio signal up to 40Khz ! In my documentation the AD converter was limited to 30Khz !
The driver consist of a character device, write to it to setup the next batch of data you want, read the data, and when finished, write to it again to setup a new batch or simply stop it. This kind of interface is easy to write and easy to handle. This is not like a network card driver that need to deal with a lot of kernel interfaces !
I still have the card and a PC with an ISA bus to use it or build a new driver
it was easy, I had already written a DOS program to use it.