OKI if800 CP/M

Chuck Guzis cclist at sydex.com
Tue Mar 15 22:34:19 CDT 2016

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...


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