Extracting CDOS and CP/M) files

[Chuck Guzis]

On 11 Oct 2007 at 13:05, Fred Cisin wrote:

> The rogue program is likely to be the OS/user.
> Many people would forget to hit ctrl-C when they switched diskettes.

In theory, that's what the feature of the CP/M directory checksum was 
supposed to avoid ("DISK R/O" error).  But I don't know if CDOS 
implemented it--and, in any case, the hole was big enough that you 
could drive a Peterbilt through it.  Earlier versions of MS-DOS also 
suffered with this problem on 360K drives with no "Disk Changed" 
line.

At Durango, we also had the problem.  It was fixed it by keeping a 
"Files Open" flag for each drive (maintained by the filesystem).  
Every 2 seconds or so, each drive's "Write Protected" status was 
polled (didn't require turning the drive motor on or loading the 
heads, so it was fast).  If it changed and there were files open, an 
audible alarm was sounded and a message saying in essence "Put that 
floppy back, idiot!" was displayed until the disk was again inserted.

The one we never could figure a way around was the customer turning 
the power off before an application could terminate and close any 
open files, update indices, etc.

The problem is still with us today. Nihil sub sole novum.

Cheers,
Chuck