Etydhv

In the version of command.com included MS-DOS, dir seems to print files in a random order, but if one runs multiple dir commands, they all print the files in the same order. This order does not appear to be based on date, size, or alphabetization. So what is the order? Does it simply print whatever files it finds first?

Whatever it finds first. DIR in MS-DOS command.com starts at the beginning of the directory table and reads it through to the end. The files will be in the order they were added to the directory table.

When a new file is created in a FAT-based file system, its entry will be placed in the first vacant directory slot, if there is one, or else the directory will be extended to add another cluster worth of vacant slots (and the new entry will be placed in the first of those). If no files are ever deleted, files will be assigned directory entries in the order of creation.

Before the advent of long file names, each file that was deleted would result in an empty directory slot, which would get filled by the next file to be created. Long file names complicate this process because they are stored using multiple consecutive directory slots (though I don't know the exact process).

The "dir" command in MS-DOS defaults to reporting files in the same order as their directory entries, but command-line arguments in later versions allow sorting by various criteria.

DIR lists files in the order they’re returned by the find first and find next calls.

On FAT file systems, RAM drives, CD-ROMs etc. this is the order of the directory entries on disk, which is file creation order as long as no files are deleted. On network file systems, it’s whatever order the server and redirector choose.

There are tools which will re-order entries on disk, to provide a permanent sort order for DIR. Defragmenting could also re-order files (commonly, directories first, then files).

DOS 5 added various sorting options to DIR itself; the order then depends only on those, when present.