Terminal Services v. VNC
Robert de Bath
list-vnc-list "at" mayday.cix.co.uk
Sat Jan 3 10:02:01 2004
On Sat, 3 Jan 2004, Mike Miller wrote:
> A friend sent me a message (not to this list), which is appended below.
> He claims that Windows Terminal Services will do for me what VNC does, but
> Terminal Services runs much faster. I'm wondering if he is correct. I
> think he's wrong about bmp encoding, for one, but is any of it correct?
In general he's right if you're on XP and to a lesser extent on 2k.
NB: I think your friend is using 'bmp' to mean any sort of generic
bitmap/pixmap -- the classic "Microsoft is everything" worldview.
If you're on XP then terminal services will normally be faster than
VNC and often more reliable. Terminal services can be more reilable
because uses it's own display driver and so doesn't have to cope with
broken display drivers, I have come across display drivers that even
**** up terminal services though.
This also applies in part to 2k, however there are two more serious
limitations on 2k
(1) Terminal services only works with the SERVER varients
-- Most people can't use it
(2) The virtual driver has a 256 colour palletted display.
-- The colours are frequently COMPLETELY wrong.
Even on XP (pro and home?) you have the artificial limitation that if
someone is connected with terminal services (remote desktop) you cannot
logon or even see the remote session from the console.
Other serious limitations of Terminal services include:
*) The server only works on NT,2k and XP nothing else not even 98.
*) Licenses. The client must be using the same version of Windows as
the machine you are connecting to, if not it'll work for 90 days
then crash until you cough up the price of a new copy of windows.
*) It uses NT logons directly without any extra authentication;
if you have one bad password on your machine it's toast because
Microsoft don't treat 'local root' exploits as a security issue.
A considerable advantage of Terminal services is that it uses a virtual
display that does NOT have to be the same resolution as the console.
If you're interested in the encoding that terminal services uses there's
an open source client called 'rdesktop'. But I think the only 'encoding'
advantage that terminal services has is that it saves offscreen pixmaps
at the client end; including font glyphs.
One thing that can improve the visible performance with VNC on windows
is using a Windows 2k/XP driver that slides in between the GDI and the
physical display driver. This improves the responsiveness and accuracy
of VNC's detection of changes on the screen. The 'UltraVNC' varient
In general, before VNC came along terminal services was a niche product
that cost a bomb and sort of worked over a LAN. Now with pressure from
Citrix at the multi-user level and VNC at the single user it's getting
to be a useable feature. Though it still costs a bomb for multi-user
or mixed machines.
Rob. (Robert de Bath <robert$ @ debath.co.uk>)