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I'm guessing there's no hard limit, but I know that performance degrades when you put too many files into a single Windows folder. Does anybody have any good rules of thumb for when it becomes noticeably slow to open a file?

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perhaps the title of this question could be amended to include a "without noticeable performance degradation"? –  Ron Tuffin Jul 31 '09 at 8:26
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6 Answers

Assuming NTFS here, in which case the technical limit is around 4 billion files. And until you go over 10s of thousands per directory you really should not worry too much.

Note however that programs like Explorer suffer much sooner than 10s of thousands, because they try to access all files in a given directory to get meta-data, etc.

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In my testing here on Win 7 Explorer is actually faster than some other tools that allegedly are more efficient. –  Joey Jul 16 '09 at 23:44
    
I haven't played with Win 7 yet, but mainly for lack of time and a good machine. I'm glad they appear to have invested some time in improving Explorer then. –  jerryjvl Jul 16 '09 at 23:49
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Look here. It says for files per volume, not per folder.

  • NTFS: 2^32 - 1 = 4.294.967.295 files
  • FAT: Approximately 4 million
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+1:There is no set limit per folder AFAIK –  surfasb Nov 30 '11 at 20:39
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Opening a file won't be very slow regardless of how many files you have in a folder. What certainly is going to kill you is enumerating files in that folder. So taking a look at the contents of that folder with Explorer, Far, dir, Get-ChildItem, whatever.

That being said, I have around 2.5k files and folders in my temp folder and display is instantaneous, so that's apparently still a small number.

ETA: Ok, just tried it, 10000 files in a folder take around one second to open that folder in Far, this and 20000 files don't even matter in Explorer.

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Just wait until you start doing that over a network. A couple apps I have to maintain like to archive everything in the same place: 100,000 or more files. Don't even think about opening that folder in explorer. –  Joel Coehoorn Jul 16 '09 at 22:48
    
Ok, agreed there. For local folders it doesn't matter apparently, I just let my copy nul %i run to 100k and Explorer takes about 1 second to open that folder, sorting the files takes a fraction of a second longer. –  Joey Jul 16 '09 at 22:52
    
@JoelCoehoorn: SMBv2 worked wonders on our machines. –  surfasb Nov 30 '11 at 20:58
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While aware of the technical "official" limitations, I just want to echo the comments of a previous post. Even in Windows 7, when you start getting beyond 10's of thousands of files, you risk corrupting whatever passes for a FAT table in NTFS (MFT, the exalted acronym for Master File Table).

It is constantly thrown in my face, yes, because of what I try to get away with when pushing the system, that these computers are NOT what they're cracked up to be. And I mean pushing WITHIN DEFINED LIMITS!

They just don't do what they're supposed to!

Let me also add that my difficulties may have also been aggravated by moving files - I suspect one is better off copying and deleting manually. Now if I could only follow my own advice...

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It depends on the file system. NTFS is way better than FAT32. FAT32 has a hard limit. However, the rule of thumb I go by is about 500 per directory.

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I have image folders with several thousand images in a single directory, and audio folders with even more. 500 is a very very low limit for a windows folder. –  TheTXI Jul 16 '09 at 22:38
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I had trouble some years ago with a directory which had about 30000 files, and new files couldn't be written (it was the "temp" directory of eMule...), it was on a FAT32 partition, but it's possible that I was using Win98 at the time, and that it was a limit of the OS itself.

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32767 is a special number because it's the maximum that representation in a 16-bit signed value; "about 30000" is close enough. –  Mark Ransom Jul 26 '11 at 18:57
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