jimomura@lsuc.UUCP (Jim Omura) (10/23/85)
It seems I was wrong about the disk level CRC. Someone on
the net has wrote to me and confirmed that floppies do have CRC
built in on the controller level. All I can say is, I've had
corrupted files load and execute under Radio Shack DOS and not
on OS-9. The program in question was VIP Writer. Keep in mind
that over the period of a year I booted VIP Writer often during
a day's work (maybe about 5-10 times per day), and it only happened
a couple of times. That's not a bad average, but it did happen.
The program loaded and executed, shot garbage all over the screen
and went dead.
Cheers! -- Jim O.
--
James Omura, Barrister & Solicitor, Toronto
ihnp4!utzoo!lsuc!jimomura
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MTS at WU: GKL6neals@tekigm.UUCP (Neal Sedell) (10/24/85)
> All I can say is, I've had > corrupted files load and execute under Radio Shack DOS and not > on OS-9. I have had this problem too. I only use BASIC so I can load a game. I transferred it from casette to disk for convenience. At first it loaded and ran every time. Then, all of a sudden, it loads, the startup screen comes on and then nothing. I use the disk so infrequently that I don't recall if I wrote to it in the interim. This is really frustrating because it should be IMPOSSIBLE to load a bad sector. When one is found the disk retrys the read and reseeks several times. Since the file loads without any reseeking we can conclude that the sector was re-written with the wrong data on it an thus was "good" in the eyes of the loader. Does anyone know what is "wrong" with Disk BASIC? I don't read Rainbow or Hot COCO so if anyone does or knows of a bug with file allocation could they please tell us about it? Could it be a problem with the SAVEM command? The file was of the default type .BIN, and I would assume James O's program was too, not that one has anything to do with the other. Speaking of OS9 and CRC's, these are only present in LOADable files (executable and device descriptors), not in text files. I think the only reason they are there is for the mentioned software in silicon concept in order to absolutely distinguish a random bit pattern from a module at boot time. You might see the header in RAM but the odds of the CRC being right is about the same as a snowball's chance in.... BTW, I have gotten "read error"s but never a "bad CRC" message when trying to execute an OS9 program (except when I had edited some of its bytes and forgotten to "verify -u" it to fix the CRC). File level CRC will detect file corruption as in paragraph 1, but only for LOADable files. I sure wish the time necessary for CRC verification was insignificant! Neal Sedell ...!tektronix!neals