Why so slow

[Brian K. White]

Jay R. Ashworth wrote:
> On Thu, Apr 29, 2004 at 02:32:01PM -0400, Walter Vaughan wrote:
>> I've tested remote desktop vs VNC, and it's remote
>> desktop by a mile.

They are two different products.

vnc is a screen scraper.
it scans the entire screen (or just the active window, depending on your
connection properties choices)
for changes, comes up with a mass of bits that changed, runs that data
through a compressor, and transmits that over the wire.
even though it's using compression and differential algorithms like
mpg/avi/quicktime movies, it's still a lot of data every time you so much as
wiggle your mouse.

remote desktop, terminal server, and citrix all take advantage of the fact
that the client and server are both running the same OS and they don't
transmit actual image data, they transmit high level windows api
instructions like "move window id 222531 50 pixels to the right and 3 pixels
down" or "change the state of button 332678 to depressed" that the remote
machines copy of windows executes similar to what a windows executable might
issue to the copy of windows it's running in to update it's own local
display. That instruction might take only a few bytes to a few tens of bytes
to send, but result in a few megabytes of display image data changing on the
remote end.

vnc might be able to optimize the update somewhat so that it doesn't need to
transmit the whole 2 megabytes of graphics, but no way is it going to come
anywhere near a few tens of bytes.

On the other hand, vnc is massively cross-platform. servers and clients
exist for many platforms, often in multiple forms such as purely java applet
viewers that run in web browsers without being installed as well as
traditional native binaries, and they all speak the same protocol so my
palmos pda phone can vnc to my windows desktop or my sco unix box with equal
ease.
I don't think remote desktop offers that. I think there exists a linux
client but no other servers.

Brian K. White  --  brian at aljex.com  --  http://www.aljex.com/bkw/
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