Dr. Bernhard Tritsch of Login Consultants publishes a detailed scalability study of Microsoft Office System 2003, Microsoft Office System 2007 and OpenOffice 2.1 on 32-Bit and X64 Windows Terminal Services. OpenOffice 2.1, while free, requires significantly more resources than the Microsoft Office Products and does not scale as well on Windows Terminal Services. (May 13, 2007)

Windows Server 2003 Terminal Server Capacity and Scaling

Terminal Services Scaling and Performance on x64-Based Versions of Windows Server 2003

Big Iron Test by Dr. Bernhard Tritsch, CTO - visionApp

TMurgent White Paper: "x64 Servers: Do you want 64 or 32 bit apps with that server?"

Capacity and Scaling of Microsoft Terminal Server on Unisys ES7000

Enterprise Application Scaling of Terminal Services on 64-Bit Microsoft Windows Server 2003

Answer:
Generally anywhere between 5 and 100, depending on the following factors:

1. Speed, type and number or CPUs installed on the terminal server.
2. Amount of RAM installed in the terminal server
3. Server's Host Operating System, i.e. Windows 2000 Server or Windows Server 2003
4. Client settings, i.e. local resource redirection, screen resolution & color depth
5. Other services running on the terminal server, i.e. Active Directory, Exchange, SQL... (NOT recommended)
6. Bandwidth available for Terminal Services sessions (a main consideration for WAN connections)
7. End-user applications being used in each session, i.e. Microsoft Office, Acrobat Reader, Internet Explorer...

Answer:
To scale-up higher than on x32 requires both RAM > 4GB and 4 or more CPUs, according to the "Terminal Services Scaling and Performance on x64-Based Versions of Windows Server 2003" study performed by HP and Microsoft.  Unisys also did a similar study on 64 Bit Terminal Server Scaling.  That being said, with sufficient resources, Terminal Server running on Windows Server 2003, Standard x64 Edition could scale to >= 150 concurrent sessions on a single server, as there is no longer the 2GB Kernel Memory Limit.

Answer:
Generally anywhere between 1 and 4, depending on the following factors:

1. In a large server farm hosting thousands of sessions on 10s or 100s of servers, 2 CPU servers ideal.
2. In a very small environment hosting only a few sessions, i.e. < 10, a server with 1 CPU is usually adequate
3. In certain environments 4 CPUs may be used, i.e. for CPU intensive applications or for virtualizing Terminal Servers on VMWare ESX or Microsoft Virtual Server.

Answers:
 

1. Scale-up means to add more resources to a server (i.e. additional CPUs or RAM) to be able to host more terminal services sessions
2. Scale-out means to add more server nodes to a terminal server farm to be able to host more terminal services sessions

Answers:
 

1. I recommend scaling-up to 2 CPUs and 4GB or RAM, at which point I recommend scaling-out with an additional server node.
2. Scaling-out is recommended because terminal servers do NOT scale-up linearly, i.e. a 4 CPU server with 8GB of RAM will NOT host twice as many terminal server sessions as a 2 CPU server with 4GB of RAM. 
3. Servers that accommodate 4 or 8 CPUs are much more expensive than those that accommodate 2 CPUs
4. Servers with more than 4 CPUs or more than 4GB of RAM require Windows Server Enterprise Edition to be able to recognize the additional resources.  Windows Server Enterprise Edition is much more expensive than Windows Server Standard Edition

Answers:
 

1. Windows Server 2003 Standard Edition is the current Operating System of choice for most Terminal Server or Citrix installations.
2. Windows Server 2003 Standard Edition is more feature-rich (to the end-user, i.e. color depth > 8bit / 16 colors and support of audio redirection) than Windows 2000 Server.
3. Windows Server 2003 Standard Edition can host more terminal server sessions than a Windows 2000 Server, assuming that the server is NOT CPU or Memory bound
4. Windows Server 2003 Standard Edition has more built-in Printer Drivers than Windows 2000 Server does.  See this Presentation on 2003 and Vista/Longhorn Memory Management improvements
5. Windows Server 2003 Standard Edition and Windows 2000 Server Standard Edition are much less expensive than their corresponding Enterprise Editions.
6. Windows Server 2003 Standard X64 Edition can scale much higher that the 32 bit version, if it is equipped with more memory, i.e. 12-16GB, Battery Backed RAID Controller, 4 to 6 SAS 15KRPM Disks @ RAID10 and 2 x Dual or Quad Core CPUs.  One must test to make sure their applications and printers are compatible with X64.

Answers:
 

1. Windows Server Network Load Balancing Service can be used to load-balance up to 32 terminal servers, however it load balances based on network load, NOT based on session count, CPU usage, available RAM...  Windows NLBS is generally only used when there is a mandate to use Terminal Services Session Directory, and often used in conjunction with a product like F5 BigIP. 
2. Provision Networks Management Framework Enterprise
3. Citrix Presentation Server (Advanced or Enterprise Editions)
4. 2X Load Balancer
5. F5 Big IP
6. Jetro CockpIT™ and Jetro BoostIT™
7. Ericom PowerTerm Webconnect
8. Centrom Panther Server
9. HOBlink JWT Enterprise Access
10. Propalms TSE (Formerly Tarantella Secure Global Desktop TSE)
11. THINWORX Server Based Computing
12. WBIsoft XPTS
13. Clusteresis RDP Load Balancer (freeware)

Answer: Yes.  See this PDF Windows Server 2003 Scalability and this presentation on 2003 and Vista/Longhorn Memory Management

Answer: Read the following whitepaper by Dr. Bernhard Tritsch, Author of "Microsoft Windows Server 2003 Terminal Services", Chief Systems Architect  at VisionApp GmbH, and MVP for Windows Server - Terminal Server.

The Big Iron Test

Also consider doing this with 64bit OS and CPUs so you're not limited by the 2GB Kernel Address Space.  Windows Server 2003 Standard X64 R2 supports up to 32GB RAM.