Msg: 5175 *Conference*

07-06-94 17:28:35

From: TRACY ALLEN

To : COMET _

Subj: REPLY TO MSG #5163 (UNDELETE -- COLD START RECOVERY)

That "impossible" was an unfortunate choice of words.  You have pointed out
that nothing is impossible!  There are some kinds of "events" that can indeed
scramble everything in memory.  But truly, if the recovery routine can get back
the .DO files, a more sophisicated routine could just as well recover both .BAs
and .DOs.  "More sophisticated" is the watchword here.  There are some programs
of that type that have been available through the years, but without something
like the XR4 to store them in, you had to find a cassette tape and load in the
recovery program.  If you had a cassette tape, you had backups of everything
anyway, right?
  
  If you cold start your computer, the first three bytes in RAM at 32768 to
32770 will be zeros, and then a 26, and the rest of RAM will be just as it was
before the cold start.  Well, there are  changes to the system directory too
and to the system pointers.  But since BASIC programs end with the 000 string
and the .DO files end with a 26  (^Z), you could write a program to scan for
"000" and assume that each 000 marks the end of a BASIC program, and update the
file directory as such.  I believe that the ^Z character does not normally
occur in BASIC programs, so you might be able to assume that when an ^Z is
found, you have passed the end of the last BASIC program and have just located
the end of the first .DO file, and update the directory appropriately.  I can
see ;you are going to have lots of fun!