I believe they did do a TCP/IP add on (or bought it in).
I found this:
«
Currently, the DESQview/X Network Manager can communicate using the following network APIs and network software: NetBIOS, Novell Netware IPX/SPX, FTP Systems PC/TCP, and Novell's LAN WorkPlace for DOS. Check with Quarterdeck Office Systems for an up-to-date list of network APIs/software supported.
»
no subject
I found this:
« Currently, the DESQview/X Network Manager can communicate using the following network APIs and network software: NetBIOS, Novell Netware IPX/SPX, FTP Systems PC/TCP, and Novell's LAN WorkPlace for DOS. Check with Quarterdeck Office Systems for an up-to-date list of network APIs/software supported. »
https://www.cs.cmu.edu/afs/cs.cmu.edu/project/phrensy/pub/www/dvx/dvxtechp.htm
I never even looked at clock interrupts, but you're right.
https://en.wikipedia.org/wiki/BIOS_interrupt_call#Interrupt_table
« 08h This is the real time clock interrupt. It fires 18.2 times/second. »
Couldn't quickly see anything about CDOS, though.