Date   : Wed, 30 Nov 1983 01:40:00 cst
From   : Eaton.HFED@hi-multics
Subject: max disk size

The answer to a very perplexing question has never beenn
satisfactorily answered until now. The question was....

HOW MUCH INFORMATION CAN BE STORED ON A HARD DISK ADDRESSED
AS ONE LOGICAL DEVICE?

The answer is a MAXIMUM of 8,388,608 bytes and ABSOLUTELY NO
MORE than 8,388,608 bytes.

I had heard the 8M figure before but no one really explained it
so that I understood why.  My bios allowed me to make it as
large as I wanted to so why not make my 10M hard disk a single
logical device.

After firing up a quick and dirty "BASIC" program to finish filling
out the remaining 3.8M of so far unused disk space (6.2M was already
filled with "good" stuff), I let it rip.  And "rip" it did.

I fully expected to see a disk full message after the mythical 8M
or at the 10M limit which my bios was genned for.  Well folks...
I eventually got the disk full message.  However....

It was printed out after my handy-dandy "BASIC" program had written
"this is a test message" throughout my entire DIRECTORY!  OH $!%*!!!

GUESS WHO ORDERED QBAX ONE DAY TOO LATE?

As to why this happened I found out with much digging that CP/M
will only handle 65,536 sectors (128 bytes each).  If you multiply
that out quickly in your head the not so mythical figure of 8M pops
out with blinding clarity.    so....

BEWARE!  THE 65,537TH SECTOR IS SECTOR 0!  THE VERY 1ST SECTOR IN
YOUR PRECIOUS DIRECTORY.     MOAN....  SO IF YOUR PUSHING RELATIVELY
CLOSE TO THE  8M LIMIT WITH YOUR LOGICAL HARD DISK DRIVES.  RECHECK
YOUR CALCULATIONS TO INSURE YOU HAVEN'T ALLOCATED 1 BLOCK TOO MANY.

signed
8megmax  a.k.a Jesse (Mpls, Mn)