Hercules mono graphic adapter

This nice vintage piece of hardware can be very usable. Unfortunatelly, by ISA bus starvation (there are no new motherboards with ISA slots for several years), the usability is still harder to find. Best thing about this solution is price - you can get Hercules card and monitor for $10 in your local computer disposal and of course kinda hackiness of such dual-head solution. Another good reason for installing Hercules is second parallel port included on most of the cards.

Second console

Probably best use is to have second textmode console with some constant information (ie. top running on server). The greatest advantage is that when local X server is started, the Hercules monitor doesn't go blank.
For doing so, compile kernel with CONFIG_MDA_CONSOLE as module and load it using:

modprobe mdacon mda_first_vc=7 mda_last_vc=9

This made new virtual terminals on tty7 - tty9. For running login on such terminals, add following lines to your /etc/inittab:

7:23:respawn:/sbin/getty 38400 tty7
8:23:respawn:/sbin/getty 38400 tty8
9:23:respawn:/sbin/getty 38400 tty9

and execute telinit q as root.
Now you can switch to your Hercules by using Alt+7 - Alt+9. If you're using consoles > 10, use AltGr+(console_no-10).

Messing with X server

Unfortunatelly, you cannot use thing mentioned above for X servers - once you start one X server on your VGA and second on Hercules, first one goes blank. (I've tested this years ago, so if this changed, please get me informed). Only option is to use Xinerama. The bad news are that Xinerama is unable to mix different pixel depths in one server, so you've got to degrade your VGA to mono adapter. For more info using Xinerama, Google it yourself :-)