I have SQL Server 2005 Express edition installed on one of my client's machine, and lots of other users are also connected to that SQL Server through the C# application that I have provided them as an interface.

Sometimes a pc get connected to SQL Server and sometimes just throw the exception

SQL Server not found....

I believe the Express edition reaches the maximum connection limit of it and then gives error.

Please guide me how could I solve this issue.

Any white paper that help me know which edition have how many number of parallel connections,

I am open to upgrade to SQL Server 2008 or SQL Server 2012, but prefer Express edition. I could go for other versions as well if they really pay me back in this context, otherwise Express edition is doing well.

  • A quick google came up with social.msdn.microsoft.com/Forums/en/sqlexpress/thread/…. It's 2008, but should be the same. Also, might want to be careful about applications connecting directly unless the account tools built into SQL Server are sufficient for security purposes. (And they're probably not.)
    – Corbin
    Dec 29, 2012 at 8:41
  • 2
    This sounds like a network issue to be honest. We ran Sql server express instances with 50-100 user doing telesales and never encountered them. When a client pc can't find the SQL server do a traceroute and some network diagnostics to eliminate it. If it is not that remember Sql server express is very limited in the amount of memory etc that it can use. If memory serves me right it will only use 1gb of ram even if you have 32gb installed.
    – Namphibian
    Dec 29, 2012 at 8:42
  • 1GB is the buffer pool limit for express edition (may use more memory for other things like connections etc) Dec 29, 2012 at 8:44
  • Last edition with limitation in concurrent users was Server 2000 msdn.microsoft.com/en-us/library/ms165672%28SQL.90%29.aspx
    – bummi
    Dec 29, 2012 at 8:47
  • @marc_s I have windows 7 32-bit on that machine and using sql server 2005 express edition with sp2.
    – MSingh
    Dec 29, 2012 at 10:00

3 Answers 3


It seems with Windows 7, you can have up to 20 concurrent connections but no more.

If you need more, you'll have to put your SQL Server installation onto a Windows Server OS.

Also see this other SO question on the same topic - SQL Server Express does not limit the number of max connections (which have a 32'768 limit on any edition of SQL Server)


SQL Server 2000 MSDE was the latest Express Version with limitations on concurrent users.
select @@max_Connections on Version 2005 + will deliver 32767.
Limitations might come from operating system.



The number of connections is not related to SQL Server edition, but to the operating system. For example, Windows XP allows only 10 concurrent connections, Windows 7 20. For Windows Server OSs, the number of connections is unlimited (but you can limit is using Terminal Services).

The error message shown in case of connection limit reached is something like "the security limit reached...the number of concurrent connect attempts"

Check out this document that compares SQL Server editions - no mention about connection limits - because there are none: Microsoft SQL Server 2012 Licensing Guide

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