VNC speed and compression

David A Vincent davidv "at" hsa.com.au
Thu, 23 Jul 1998 10:26:15 +0000


Diego Sierra <dsg "at" ll.iac.es> writes:

> I run the vnc server on a PC with Windows95 and open a session from
> another PC or an unix workstation. Why is so slow when sending
> information to the client (i.e. updating the screen) ???,
> 
> The system is running on a switched Ethernet (10Mbps), and there is
> absolutely no traffic congestion. VNC version is 3.3.2, and Hextile
> encoding.

In this kind of setup the speed of the system is limited by the speed
of the server, rather than by the speed of the network.  The system is
slow because WinVNC is taking a long time to figure out what
information to send, not because the network is taking a long time to
send it.  

I find the VNC server (WinVNC) unusable on a 100MHz Pentium, but just
bearable on a 200MHz machine.  In practice I avoid running WinVNC at
all.  A month or so ago I swapped the Sun box on my desk for a 100MHz
Windows box.  Using Xvnc on other Sun boxes in the office with
vncviewer on the PC provides perfectly acceptable X desktop
performance, while I can run Windows applications locally.  Doing
things the other way around (Sun viewer and Windows server) was just
not working, at least with the speed of Windows machines we have
available at the moment.  

This topic has been discussed several times on vnc-list, and is
probably a FAQ.  I think it's been said that the Windows display
architecture is very crude compared to that of the X window system, so
the Windows server is necessarily more complicated and slower than the
X one.

> It seems that laplink via a 14.4 modem connection (with compression),
> using the same both PC's, is even faster !!!.

VNC is a more general-purpose tool than LapLink, which would be no use
at all for the most of the jobs I currently use VNC for.

...dav
-- 
David A Vincent   <mailto:davidv "at" hsa.com.au>    JUNK E-MAIL NOT WELCOME
Working (not speaking) for      Hydrographic Sciences Australia Pty Ltd
HSA phone extension number 27    within HSA, web site <http://marilyn/>
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