Date:	Thu, 27 Feb 1997 22:20:50 -0600 (MDT)
From:	Roger Ivie <IVIE AT cc DOT usu DOT edu>
Subject:	[opendos] CP/M use of high bits in filenames; was: Wishlist part 2
To:	OPENDOS AT MAIL DOT TACOMA DOT NET
Message-id:	<01IFXD1YP5WI8YSMTY@cc.usu.edu>
MIME-version:	1.0
Sender:	owner-opendos AT mail DOT tacoma DOT net

> High-bit set characters have a special meaning under FAT, AFAIK. They
> certainly did under CP/M. I think if the first character has its top bit
> set
> that marks the file as being deleted.

AFAIK, the only character which has a special meaning under FAT is 0xf6,
and even then only as the first character in the name.

Under CP/M, the first character in the directory entry was not the first
character of the name. It contained the user number (0x00 through 0x0f) for a
file which was not deleted or 0xe5 for a deleted file. If it contained anything
else, you couldn't get to the file. 

The high-order bits of the filename characters were used to store file
attributes. The only defined attributes were Read-Only and System (called
Hidden in DOS). The remaining bits were available for users.

IIRC, DOS provides an attributes byte in the directory entry so it doesn't
need the high-order bits of the characters for file attributes.

Roger Ivie
ivie AT cc DOT usu DOT edu

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