Mouse: IBM PS/2 bus mouse compatible. No drivers are needed. Say Y to bus mice and to PS/2 in the kernel configuration. X11 and gpm will happily talk to this device, although most people find the little button mouse quite painful to use.
Modem: The modem appears as a standard serial port and you can pick which you want to use in the BIOS. It does 2400 baud or 9600 baud FAX and includes voice. As it isn't approved for telephone connection in the UK I've not been able to play much with this option.
IrDA: The IrDA port implements the IrDA physical layer but expects software to provide the upper layers. Fortunately as with most IrDA ports you can throw all the IrDA rubbish away and just run SLIP or PPP between your PC110 and a base machine. This is very important as without base station IrDA is about all you get in I/O. Again it appears as a standard serial port. The port has no handshaking or carrier on it in this mode so you need to use the -L option if you use slattach to set it up for SLIP. We were able to get about 3 metre range at 115,200 baud.
PCMCIA: The Linux PCMCIA drivers leave the hard disk alone but will handle the other slot happily if you are using an extender. The PCMCIA package includes drivers for a wide range of useful PCMCIA devices and handles hot swapping.
Digitizer Pad: This is used to allow you to scribble memos in the Personaware application. I wrote a simple driver for it under Linux which Robin O'Leary has extended to do some of the PS/2 mouse handling and when complete will support glidepoint style 'tap' behaviour. Current snapshots of this can be found on Robin O'Leary's PC110 site.
Hard Disk: On my PC110 the supplied disk does not support the spin down as I'd expected. Hdparm will allow you to set an idling time and the drive seems to reduce both speed and power when it idles, but it does not spin down. I am currently planning to write some PCMCIA hooks into the IDE driver for the PC110 to turn the drive on and off after several minutes as having the drive spin down from my test runs ups battery life by over an hour.