What's the technical explanation of the way VNC does it's screen updates compared to other remote control systems?

Nicholson, Rob rob.nicholson "at" informed-direct.com
Thu Apr 15 17:49:01 2004

Over the years, I've used a whole variety of remote control systems all of
which, at their core, do the same thing. They make what's drawn on one
screen (or buffer) appear at the other end of the wire and send
keyboard/mouse events back the other way.

We're very impressed with VNC mainly because it's saving us money over
pcAnywhere licenses :-) But to be honest, it's screen refresh technology
whilst perfectly adequate, isn't as slick as some other tools I've used:

o Citrix Metaframe: works amazing well over dial-up connection. That ICA
protocol really hums
o GotoMyPC: very impressive as well but only ever used it over broadband.
You do forget you're remote controlling
o pcAnywhere: considering this is/was the market leader, it's refresh
technology is pretty naff

So do all these systems work in the same kind of way? Maybe keeping a copy
of the screen between frames and only transmitting the differences, in a
compressed data stream?

I suspect that Citrix does it in a far more integrated/deep down method as
it's part of the operating system. It's feasible it intercepts individual
paint events!

Just interested really...

Cheers, Rob.