Windows 8 / IIS 8 Concurrent Requests Limit

IIS 8 on Windows Server 2012 doesn’t have any fixed concurrent request limit, apart from whatever limit would be reached when resources are maxed.

However, the client version of IIS 8, which is on Windows 8, does have a concurrent connection request limitation to limit high traffic production uses on a client edition of Windows.

Starting with IIS 7 (Windows Vista), the behavior changed from previous versions.  In previous client versions of IIS, excess requests would throw a 403.9 error message (Access Forbidden: Too many users are connected.).  Instead, Windows Vista, 7 and 8 queue excessive requests so that they will be handled gracefully, although there is a maximum number of requests that will be processed simultaneously.

Thomas Deml provided a concurrent request chart for Windows Vista many years ago, but I have been unable to find an equivalent chart for Windows 8 so I asked Wade Hilmo from the IIS team what the limits are.  Since this is controlled not by the IIS team itself but rather from the Windows licensing team, he asked around and found the authoritative answer, which I’ll provide below.

Windows 8 – IIS 8 Concurrent Requests Limit

Windows 8 (Basic edition) 3
Windows 8 Professional, Enterprise 10
Windows RT N/A since IIS does not run on Windows RT

Windows 7 – IIS 7.5 Concurrent Requests Limit

Windows 7 Home Starter 1
Windows 7 Basic 1
Windows 7 Premium 3
Windows 7 Ultimate, Professional, Enterprise 10

Windows Vista – IIS 7 Concurrent Requests Limit

Windows Vista Home Basic (IIS process activation and HTTP processing only) 3
Windows Vista Home Premium 3
Windows Vista Ultimate, Professional, Enterprise 10

Windows Server 2003, Windows Server 2008, Windows Server 2008 R2 and Windows Server 2012 allow an unlimited amount of simultaneously requests.

17 Comments

  • Hi scott, does windows 8 mean enterprise edition? if that's the case, why professional has more concurrent request than enterprise?

  • Are these IIS limits, or HTTP.SYS limits? Would they impact a .NET program using the HttpListener?

  • @javafun, the naming in the editions for Windows 8 is confusing in that regard, but "Windows 8" edition is really the home edition. I just updated the post to mention that, and also to mention Enterprise edition.

  • @Eric, I had to ask to get the answer on that. The limits are implemented in IIS specifically on the hand-off from http.sys. So, it would not affect other consumers of http.sys.

    There may be other limits unrelated to this, but this particular limit wouldn't impact a http.sys based HttpListener.

  • Hi scott,thanks for your update, I wasn't realized there is a home edition at all :)

  • Thanks, but what about IIS ftp connections?

  • Hi John,

    Good question. Yet another question I had to look into to confirm for sure. There isn't any FTP throttling in place.

    Scott

  • Is anyone aware of the of the concurrent request limit for Vista Enterprise 32bit?
    Vista Ent is an OEM only / non retail version of Vista that shares some characteristics of Vista Ultimate such as BitLocker but not all of them such as the Vista Ultimate multimedia features.

    Web research seems to explain these limits for every version EXCEPT the obscure Vista Ent.

    Thanks in advance

  • Hi Curio. You're right that Enterprise doesn't appear to be mentioned in the lists regarding this functionality. I updated my post to include it. It's in the same category as Ultimate and Professional with a limit of 10 concurrent requests.

  • Hi Avram,

    It may be possible that Windows 2012 Essentials follows yet another pattern. I'll try to find an authoritative answer for you.

  • Hi OWScott,

    I've some query regarding the Concurrent Request Limit vs Queue Length in IIS 7/7.5/8:

    Case 1: Windows 7 Professional
    Concurrent Request Limit=10
    Queue Length=1000 (as default)
    if concurrent requests to IIS is 50, does it means only 10 concurrent requests will be handle, the rest of 40 will be queue?

    Case 2: Windows Server 2012
    Concurrent Request Limit=Unlimited
    Queue Length=1000 (as default)
    if concurrent requests to IIS is 50, does it means all 50 concurrent requests will be handle? none of the requests will be queue?

    Thank you.

  • Hi Lee MY,

    Yes, that's correct. Note that many requests can be completed in under a second so 50 concurrent requests even on Windows 7 can often be fulfilled without any perceived delay, but technically how you described it is correct. Windows 7 has a purposeful throttle for the number of concurrent requests so that it doesn't have the same performance as the server editions. Also note that other factors can cause different delays (database, web services, block threading, etc), but at least it's not purposeful.

  • On 8 Jan 2013, OWScott said: "It may be possible that Windows 2012 Essentials follows yet another pattern. I'll try to find an authoritative answer for you." Any word on that yet? Lots of us are trying to find out whether Windows Server 2012 Essentials would work as a regular public-facing IIS web server (i.e. do the job that Windows Server 2008 Web Edition did). Thanks.

  • Hi Richard,

    I never did get an answer back on that particular question. IIS installs on Windows Server 2012 Essentials and it will run, but it will contend with AD and other services on the server so it's not necessarily the best solution for hosting websites. It will work though for a stepping stone solution. I wasn't able to find the concurrent requests limit for Windows Server 2012 Essentials. It's managed by a different team and I didn't have any success in tracking down the answer.

  • Can we increase the concurrent connection limit in windows 7??

  • Hi Pratish,

    No, it can't be changed. That limit is set by the OS on purpose to prevent Windows 7 from being used for high traffic web server solutions, which Windows 7 isn't intended for.

  • It also seems like in Windows 8.1 "Home edition" you cannot enable the IIS feature "Windows Authentication", pretty annoying... :(

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