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Nearly every setup I know shows something like this at the beginning:

enter image description here

There is a text saying:

"Computing space requirement"

This sometimes runs just a few seconds and sometimes significant longer.

Since checking for free disk space is to me the equivalent of simply calling fsutil volume diskfree c: which takes about one second maximum, the message seems to be an euphemism for:

"we are doing something here and won't tell you what."

I've already tried to use Process Monitor to see what's going on but found nothing significant.

I can think of:

  • Extracting the MSI content.
  • Looking in the Registry or file system for previous installations.
  • …

While there might be no general answer for all setups out there that print "Computing space requirements" what they are actually doing, maybe there is a rule-of-thumb.

(My example screenshot was taken randomly from Markdown Edit which uses the WiX Toolset)

My question:

What happens during setup execution when the setup is busy and writes "Computing space requirements"?

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3 Answers 3

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It is determining how much of the program it must install, and determining what the size on disk will be. There are several contributing factors, like the features the user has selected for installation, and the state of the current system.

Many programs rely on shared dependencies, but if those dependencies do not ship with the OS, or ship different versions of those libraries, the application may have to install them itself. Or, it may be that another program has already installed it.

This means that the actual disk impact of installing a program may vary widely. It takes time to search the disk and registry to determine if the dependency is already available on the system, so the UI displays this message to tell you what it is doing.

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I think it's like asking, how many ways can you make a martini? You are exactly correct. It depends on the software, who wrote it and what "they" are computing or searching or gathering or delving... The answer is yes. And if you were to install the same program one time, then uninstall it, then reinstall it and time each install it could take two very different amounts of time. Your computer also has a schedule of events. Also you are doing things. You may arrive at the office everyday at 8am, but it might take different times. And then there is a thing called priority in computer science.

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One of the basic requirements for a software installation is Disk Space.

For example:

http://windows.microsoft.com/en-in/internet-explorer/ie-system-requirements#ie=ie-11

What happens during "Computing space requirements" ?

While installation wizard shows computing disk space, it is checking if you have enough disk space as required by the software or not.

All the good software do this check to prevent un-necessary errors after installation. However it varies how they do it.

Some do it silently while some like to show you a message.

Look at this installation error for example:


(source: trendmicro.com.au)

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  • Isn't checking for free disk space the equivalent of simply calling fsutil volume diskfree c: which takes about one second max?
    – Uwe Keim
    Commented Jun 10, 2016 at 8:14
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    BTW: I like how your screenshot's title says "Worry-free" and then tells you something to worry about ("Not enough disk space").
    – Uwe Keim
    Commented Jun 10, 2016 at 8:16
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    @UweKeim hehehe...just grabbed something from google. Time it takes to do that is/must be dependent on how they do it, what technology they use etc. You know there are more than 2 ways to check free space. Some might check file system while some might skip it. who knows
    – clhy
    Commented Jun 10, 2016 at 8:24

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