This is a two part question.

How much free disk space is recommended for windows (on the os drive and non-os drive) to function properly?
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William FulksSystems Analyst & WebmasterCommented:
Windows 7, for example, recommends 16 gig for 32-bit and 20 gigs for 64-bit.

What's the second part of your question?
Lee W, MVPTechnology and Business Process AdvisorCommented:
Who still uses Windows 2000?

2003 is RETIRED and shouldn't be used.  PROPERLY MANAGED, 20 GB on a new install given that you should be moving away and any new install should be temporary to support migration of a LOB app.  For ongoing functioning, again, assuming configured appropriately, I would want 20% free (4GB).

Microsoft has recommendations.  I have different recommendations:
Windows 7: 80 GB
Windows 8: 60 GB
Windows 10: 60 GB

Can you get by with less on the above?  YES... but start installing apps, Outlook, etc, and your space will get RAPIDLY eaten.  The above recommendations are mine for a MINIMUM for installing assuming you configure appropriately. Once running, I would recommend AT LEAST 10 GB free.  But of course, it depends on the apps you use and what kind of temporary storage they might require.

For servers, 2008 and 2012, I would recommend a 120 GB C: drive.

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Scott CSenior EngineerCommented:
I think the second part to the question was the non-os drive.  That would depend on what the non-os drive is used for.  Do you have the page file on it?

For the non-os drive it's not as critical because if it fills completely up the OS won't crash.
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We_Support_ITAuthor Commented:
You would be surprised how many people still have 2000 server. I have one customer that i still support a windows 3.11 "server" because it still works for what they need and the new hardware and software would cost them 250k plus installation time.

I agree that the 20% free is a good starting point on the OS drive and small storage drives.

The non-storage drive would not have have any paging file on it. This would be the repository for media files and some documents.
JohnBusiness Consultant (Owner)Commented:
I have Windows Visa, 7, 8 and 10 Virtual machines installed. I allow 100 GB for each machine.

Windows Vista with Office 2007 and a fair amount of software takes 53 Gb
Windows 7 with Office 2010 and a fair amount of other software take 43 GB
Windows 8 with no Office uses about 25 GB (not a working machine)
Windows 10 with Office 2016 and little other software takes 27 GB

So I suggest 100 GB partitions if you can manage it.
You did not ask how much space windows needs for itself, but how much space should still be free to "function properly"? It will function properly with only some MB left, really. It will get slower if only some GBs are left and fragmentation starts to get a problem. As for the second part: windows does not care how much space is left on non-OS drives, you can fill those up.

Of course, no expert would let it come that far. All format their drives with enough spare space in mind. How big those partitions should be depends entirely on what you would like to do with it. Slim installations will be ok with 20 GB, but most office computers will have at least 50 if not 100 GBs.
Windows 10 x64 (without pagefile and without hiberfile) itself occupies just as little as 8 GB.
JohnBusiness Consultant (Owner)Commented:
Over time I see lots of questions in here about too little disk space after time, service packs, and updates. Better, in my opinion, to opt for as much as is practical.
Spike99On-Site IT TechnicianCommented:
I wouldn't scoff at people using Windows 2000. I was at a customer site in February of 2014: they still had Windows 95 workstations in use!  This was a medical facility & these Win95 machines were configured basically like thin clients: all they could do is use Citrix Program Neighborhood to connect to the server.  So, the CNAs used those machines to connect to the Citrix server to enter their notes in the patient's electronic medical chart.    I managed to edit the Citrix PN connection so it would connect to our Citrix servers, so they could continue using them.

I don't work for that company anymore, but I wouldn't be surprised if they're still using them.
William FulksSystems Analyst & WebmasterCommented:
We had a client that was also a medical office and they still had to use IE8 and some ancient version of Java for one of their apps. It could costs a bunch of $$$ to upgrade the core software and so they opted not to do so, but would still call tech support when certain websites wouldn't look right in IE8!
i would like to know why this question is asked, eg does he have problems, or is this only a theoretical one?
if he has problems, he better start giving more info on the hardware used, and the problem itself
We_Support_ITAuthor Commented:
Working on a creating a standard quoting process of and want to have a formula to show required minimum free space on OS drive and non os drives. This way we know how much buffer we have.
ok  - then you can pick one of the above posts
I've requested that this question be deleted for the following reason:

Not enough information to confirm an answer.
JohnBusiness Consultant (Owner)Commented:
There was lots of information here that answers the question.

I suggest http:#a40895972 and  http:#a40896126
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