On 27 Aug 2001, Christopher Mellen <cmellenat_private> wrote: > If I understand it correctly the CRC at the end of the data area of a > sector is generated when a sector is written to. Two CRCs, actually: one for the data, and another for the address markers. > Subsequently, the CRC is checked when the sector is read - if the CRC > value doesn't match then it's flagged as bad and some type of error > should occur. Right. If it's the DataCRC, then you get a "Data error reading drive <x>" message; if an address CRC, you get a "Sector not found", at least under DOS. Other OSes no doubt have their own error messages. > So my question, if I use a disk utility such as diskedit and change > the data area (i.e. add a line of text to a document) in a sector. > Why then does the sector CRC not report an error when accessing the > file normally at a later time? Because the BIOS is smarter than to screw up the data. :-) > or is this done with an ECC and it's correcting it on the fly as > there would be no physical issues with the sector...? Using a WriteSectorLong call will allow changing the actual data while setting whatever ECC code is specified. As for monkeying with the Address fields and associated CRC, that's a segue into LLFs. > thanks Sure. -BPB University of Michigan AntiVirus Team Leader University of Michigan Data Recovery Team Leader PGP 2.6.2 key fingerprint: 0D A5 98 3C 91 DA E0 DD 9C 6D FA 8F 4D 34 95 ED ----------------------------------------------------------------- This list is provided by the SecurityFocus ARIS analyzer service. For more information on this free incident handling, management and tracking system please see: http://aris.securityfocus.com
This archive was generated by hypermail 2b30 : Mon Aug 27 2001 - 12:25:58 PDT