ET> What's the difference between a PS/2 mouse and a serial mouse, apart
 ET> from the port? They use both an IRQ and an address, right?
A serial mouse is connected in the same way as an external modem is, and the
driver talks to it via the appropriate UART.  A serial mouse driver has to
allocate the IRQ and I/O port numbers of the UART.
A PS/2 mouse is connected, via a different sort of connector, to the keyboard
controller chip, and the driver talks to it by sending commands to the 
keyboard
controller.  This is why the PS/2 mouse driver has to cooperate with the
keyboard driver.  Only one thing can be talking to the 8042 chip at any one
time.  A PS/2 mouse driver allocates the I/O port numbers of the keyboard 
chip,
sharing that allocation with the keyboard driver (run RMVIEW /D at an OS/2
command prompt to see this for yourself).
 ¯ JdeBP ®
--- FleetStreet 1.19 NR
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