In article ,
Scott Skylane wrote:

Here's a cockpit shot of one of the 1900s he flew:
http://www.airliners.net/open.file/0585758/L/

On a completely unrelated note, I see there is a vacuum suction gage on
the instrument panel. What is this for? Apparently all of the "gyro"
instruments are electronic.

Correct. There are four remote gyroscopes (two attitude gyros, two
heading gyros), all powered by 115-Volt AC power. The really nice thing
about that kind of system is that if one gyro dies, you can route the
signal from the working gyro to both screens, so each pilot still has a
full set of instruments. Pretty neat.

There's also a standby attitude indicator, which has its own internal
battery backup. You can see it above and to the left of the GPS in the
picture linked above.

Is this strictly for the de-ice boots?

Deice boots, and the operation of the pressurization's outflow valve.
(Suction pulls it open; springs push it closed.) That works fairly well
for a plane that size; larger planes, like the 737, have an
electrically-operated outflow valve.