Theoretically, it is unlimited. There are practical limits but it is different for each customer.

We have many customers hosting between 5 and 30 sites in a VDH account, depending on configuration, resource use and cost.

If you host the sites without VDH add-on packages, all of your applications will share one IIS virtual server and run in the same dedicated server process. This is the most practical and cost effective way to host many sites for one low fixed cost.

There are advantages for using the VDH add-on packages (see sales article 16187 http://www.aspwebhosting.com/KBArticle.asp?ID=16187), however, you will run into limits based on cost and resource allocation.

Resources are allocated as follows:

1) Web site disk space is 2.5GB total to be shared between all applications (sites), regardless of whether you use VDH add-on packages or not.

2) SQL Server disk space is 2.5GB total, however, if you buy VDH add-on packages each add-on can have a portion of that disk space allocated to a unique database. If you implement a site without a VDH add-on package, you cannot have a separate SQL database (excluding MS Access) for that site and it must share your master SQL Server database.

3) POP3 accounts are unlimited, however, if you do not buy a VDH add-on package that comes with virtual mail server, your POP3 accounts must share a virtual mail server (using a mail alias name) and you cannot duplicate POP3 mail box names across multiple domains. In other words, if you have mail.domain1.com and mail.domain2.com, you cannot configure sales@domain1.com and sales@domain2.com unless they are on separate VDH add-on packages. In addition, there is a limit of 256 characters to mail aliases which limits the number of domains that can be added as a mail alias.

4) Memory is limited to 128MB of RAM. This can be a limiting factor, however, rather than enforcing these limits, we are inclined to provide consultation to our customers providing them practical techniques for reducing their applications RAM use. Often we find that simple changes in programming habits can reduce an applications RAM use significantly.

While implementing VDH add-on packages provides a myriad of benefits, there is a practical point where it becomes more cost effective to upgrade to a dedicated server. You may also reach the physical limits of resource allocation and be forced to upgrade to a dedicated server or buy a whole new VDH account.