On 03/15/2016 07:08 PM, Charles Anthony wrote:
I have a vague late-70's memory of RSX-11 putting the directory in
the middle of the disk.
Not unknown in the CP/M world. For example, the NSC BLC 86/20 puts the
CP/M directory on cylinder 39 of a 3.5" floppy. CP/M had all sorts of
strange and original ways to map out a disk.
The "list of clusters" wasn't new even in the 1960s. Take CDC SCOPE for
example, using an RBT (list of clusters--Record Block Table), read into
memory when a file was opened.
ISIS II had a similar scheme of lists of blocks belonging to a file.
Practically speaking, it was a lousy way to organize a floppy disk.
Better to create contiguous extents for a file with an option for a
number of additions, which keeps data belonging to a file together.
Anyone who's tried to recover a MS-DOS floppy used as a work (lots of
read/write/open/close activity) volume where both the root directory and
FAT have been wiped out knows how hard that can get be. The stinker is
that on a floppy, those were usually located on cylinder 0, where,
incidentally, the FORMAT command also started writing...
--Chuck
