Applies To:
  • CitectSCADA 1.00 1.01 1.10 1.11 1.20 2.00 2.01 3.30 4.10

Question: What operating system do you recommend to run Citect under. Windows 3.x, Windows 95 or Windows NT? 

Here are the features and limitations of each of the operating systems you can run Citect under.

Windows 3.x

  • Most Citect drivers are available. Some new drivers will only be developed for 32 bit versions.
  • The operating system is stable when setup correctly and running Citect alone. If you have setup anything incorrectly then Windows 3.x can fail and give no indication of why it fails. This makes it very difficult to find the cause of a problem. This is typical when device drivers are faulty, you have clashing interrupt, io ports or memory, incompatible TSRs or buggy applications. Windows 3.x can also fail under low memory conditions.
  • You can run other small applications at the same time as running Citect. Running complex programs which require large use of CPU or disk access can severely degrade the performance of Citect.
  • Graphic display can give problems due to the reliability of poorly written drivers, see Q1119.
  • If you are running a second application with Citect on the same computer which consumes lots of resources then Citect performance will be degraded.

Windows 3.x has been a good operating system in the past. If you have no existing problems with your current system running under Window 3.x then it is OK to stay with it. If you are installing a new system then you should look at Windows 95 or Windows NT.

Windows 95

  • Not all 32 bit drivers are available at this time . If you need to use a driver which is only available in Citect 16 bit versions you can run the 16 bit version of Citect under Windows 95.
  • Much more stable operating system than Windows 3.x. More resilient to failure when setup incorrectly, while plug and play will prevent most problems from occurring. The memory protection is superior to Windows 3.x and much more reliable under low memory conditions.
  • The multi thread support works well with 32 bit applications, however it does have limitations when running 16 bit applications. Also the 32 bit multithread does not have the same level of support as Windows NT. This becomes apparent at the driver level for various low level devices. For example the printer driver in Windows 95 does not support multithreading to the same extent as Windows NT. If a 16 bit application hangs on the printer port then all 32 bit applications may hang. This type of problem does not occur under Windows NT. This can also be the case for the serial ports and disk I/O. These type of problems have been shown to cause communication breaks when high disk activity is occurring. This problem does not occur under Windows NT. So Windows 95 is not a good operating system when you are using Serial protocols.
  • Good performance when running heavy weigh 32 bit applications with 32 bit Citect in same computer.
  • Graphics performance is fast and equivalent to Windows 3.x. Graphic drivers are more stable due to enhancements in the driver model.
  • Gives good performance when running on 486/66 class computers. If you are upgrading an existing Windows 3.x system and your hardware is less than a Pentium then Windows 95 is also a good choice. Windows 95 will run well on lower performance (486/66 8M computers) computers.
  • Citect running Windows 95 under does not disable Ctrl-ESC, Alt-ESC, Alt-Tab etc yet, so operators can get into operating system. You can run Citect as the shell to prevent this see Q1084.
  • There are some problems with slow network performance see Q1874 for details (We have worked around these limits with version 4.20). There are some problems will high performance and time critical serial protocols. This makes these serial protocols unable to run reliably under Windows 95, see the protocol documentation for details.
  • Excellent support for 16 bit applications. You can run the 16 bit version of Citect with drivers which are not supported in 32 bit. This gives you some of the benefits of Windows 95 with all the drivers from version 3.x of Citect. Citect version 3.21 and 3.30 run perfectly under Windows 95.

This is a good choice for a Citect client or if you want to upgrade from Windows 3.x and you hardware is not fast enough to run Windows NT.

Windows NT 3.51 and Windows NT 4.0

  • Windows NT may not have all the drivers you require. If you have a very new or very old device it may not be supported. This could include graphic cards, printers, modems, etc. You should verify that a driver exists for all your devices. Check the Hardware Compabilty List from Microsoft to see if it is supported. This is very important, make sure your printer and graphic cards are supported under Windows NT before you buy the hardware. The very latest hardware devices may not be supported.
  • Basically bullet proof operating system and significantly more stable than Windows 95 and Windows 3.x. Full memory protection for all applications and very reliable. Windows NT will not allow you to configure hardware cards with clashing interrupts io ports or memory regions as all hardware setup is controlled by Windows NT Registry. If there is a hardware failure or faulty device driver, Windows NT will trap the error and you will be able to find the cause (See Q1896).
  • Windows NT is not as compatible as Windows 95 or Windows 3.x with older DOS or Windows 16 bit legacy applications. This may cause these application not to run correctly under Windows NT. This may be the case for older PLC programming tools or any software which requires DOS TSR's or interfaces directly to the hardware.
  • Multi threading support has no limitations with 16 bit applications as with Windows 95. There are no resource limitations, you just add more memory to get more performance. So excellent choice when you must run many applications at the same time.
  • We have found that Citect Graphics performance is typically 15% slower than running on Windows 95 or Windows 3.x on the same hardware. This is due to Windows NT extra level of protection. Using high performance graphic cards does not greatly improve performance as most of the overhead is in the protection of NT and so tends to be CPU bound. Increasing the performance of the CPU will help this problem. If you only want to use the Windows NT computer as a Citect server (ie no operator graphics) this is not such a problem.
  • Requires more memory and faster CPU to get the same level of performance from Citect. You should use at least 100 MHz Pentium class computer with 24 M of RAM for a standard Citect project and a large Citect project may require up to 32MB of RAM. If you are running many applications you will require more RAM. If you want to use the Windows NT computer as a file server you should also add an extra 8 to 16MB of RAM. The Citect server functions of Citect will run just as fast or even faster under Windows NT than Windows 95 or Windows 3.x.
  • Excellent security, reliability and network management.
  • Excellent solution when you want to run Citect servers and a File server in the same computer.
  • There are some problems with slow network performance see Q1874 for details (We have worked around these limits with version 4.20).
  • You can run the 16 bit version of Citect with the following limitations. Citect will not be able to access the software protection key, so you must have a key on a Citect server running under Windows 3.x or Windows 95 on your network. Only serial protocols will may work.

This is an excellent choice for a very robust Citect system on new installations. I expect that over time all new installations of Citect will be under Windows NT, so you may as well start using it now.

The Choice

I no longer recommend the use of Windows 3.x as a operating system to run Citect on. I also don't recommend the use of Windows 95 if you are using serial protocols.

The first choice of operating system should be Windows NT 4.0, the second choice should be Windows 95 and the last choice is Windows 3.x. To chose which operating system you should first look at Windows NT and see why you cannot use it. If you cannot use Windows NT then look at Windows 95 and see why you cannot use that operating system. If you cannot use Windows 95 then your only choice is to use Windows 3.x. CIT is committed to all future development on 32 bit operating system only. We are also focusing our attention on Windows NT 4.0 and use Windows NT 4.0 as our primary development and testing platform.

The following should be the only reasons why you cannot use Windows NT or Windows 95.

Reasons why you cannot use Windows NT:

  1. Driver not available. Check to see when your driver will be available in a 32 bit version as there are many new 32 bit drivers under development.
  2. Need to run legacy 16 bit applications which will not run under Windows NT.
  3. Upgrading existing system and hardware does not have enough CPU or memory to run Windows NT.
  4. Want to run on a portable computer and need the plug and play support of Windows 95.
  5. Because the client does not want Windows NT. (It is up to you to try to convince the client to the benefits of Windows NT).

Reasons why you cannot use Windows 95:

  1. Upgrading existing system and hardware does not have enough CPU or memory to run Windows 95. Normally added 8 Mb more memory will resolve this problem.
  2. Because the client does not want Windows 95. (It is up to you to try to convince the client to the benefits of Windows 95).

Finally Citect version 3.x and 4.x is totally absolutely compatible. You can run the same project at the same time under all operating systems. You can configure under any operating system. So it is very easy to change from one operating system to another. This way if you have an existing Citect 3.x system running under Windows 3.x you can add a Citect client running under Windows 95 or Windows NT. You can do this without upgrading your project or effecting any other computer on the network. This allows you have a look at the features and to test the Windows 95 or Windows NT system while still running your legacy Windows 3.x system.