There are limits, of course.
The limit most people run into first is the size of their hard disk, but assuming you have a big enough disk, other limits can come into play.
I will say this right away, though: the size of the files in a single folder turns out not to be one of them.
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File size limits
There’s no practical limit on the combined sizes of all the files in a folder, though there may be limits on the number of files in a folder.
More importantly, there are limits on individual file size that depend on what file system your hard disk uses.
A file system is nothing more than the specification of how files are stored on disk. In practice, it is generally synonymous with “format”, as in, it’s a choice made when a disk is formatted. Limits are one factor in choosing which disk format to use.
FAT / FAT16
FAT, for File Allocation Table, is the successor to the original FAT12 file system that shipped with MS-DOS many, many years ago.
- Maximum disk size: 4 gigabytes
- Maximum file size: 4 gigabytes
- Maximum number of files on disk: 65,517
- Maximum number of files in a single folder: 512 (if I recall correctly, the root folder “/” had a lower limit of 128).
FAT32 was introduced to overcome some of the limitations of FAT16.
- Maximum disk size: 2 terabytes
- Maximum file size: 4 gigabytes
- Maximum number of files on disk: 268,435,437
- Maximum number of files in a single folder: 65,534
NTFS, or “New Technology File System”, was introduced with Windows NT, and is a completely redesigned file system now standard on most new Windows machines.
- Maximum disk size: 256 terabytes1
- Maximum file size: 256 terabytes
- Maximum number of files on disk: 4,294,967,295
- Maximum number of files in a single folder: 4,294,967,295
exFAT is an extension of the FAT file systems originally designed for embedded systems and flash memory. While not as rich in features, it’s somewhat more cross-platform compatible and lighter weight than NTFS.
- Maximum disk size: 128 petabytes
- Maximum file size: 16 exabytes2
- Maximum number of files on disk: 4,294,967,285
- Maximum number of files in a single folder: 2,796,202
Disks versus disks
Note that when I say “disk” above, I’m really talking about “logical” disks, not necessarily physical ones. This shows up in two ways:
- Disk partitioning can make a single physical disk appear as multiple logical disks.
- Multiple physical disks can be arranged to appear as a single logical disk using various techniques, including RAID arrays or disk striping.
For example, no one (currently) makes a 256 terabyte disk drive, but using these techniques, you can treat a collection of disk drives as a single logical disk. NTFS is particularly suited to this task.
Realistically, the size of your disk, or rather, the amount of available space on the disk, will almost always be the first limit you hit.
If individual files exceed 4GB, then avoid FAT, FAT16, and FAT32 file systems. NTFS and exFAT will handle individual files well over that size.
There’s really no limit of the aggregate size of the files in a folder, though there limits on the number of files in a folder.
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Footnotes & References
1: This limitation may simply be an implementation restriction. I’ve read that the NTFS format can support disks up to 16 exabytes (16 times 1,152,921,504,606,846,976 bytes).