dolf@fwi.uva.nl (Dolf Starreveld) (11/13/89)
cash@zug.csmil.umich.edu (Howard Cash) writes: > If you are considering upgrading your Mac to a IIci you may be in for > a surprise with your external hard drive. Certain manufacturers > did not exactly follow Apple's scsi guidelines and now they are being > bitten. > According to someone I spoke to at Apple DTS, at least three disk drive > manufacturers have made disks that will not automount on the IIci. There > may be others. The same source at Developer Technical Support says that > all of the manufacturers with this problem have acknowledged their errors > in this regard and will upgrade their hardware for affected customers. One of the reasons an external (non-Apple) drive may fail to automount is that the Mac IIci is one of the first machines (the Portable is the other) that checks the checksum of any driver it attempts to load against a checksum stored in the partion map entry describing that driver. All this stuff is explained in Inside Mac V pp. 580-582. A recent Technote describes that, although this checking process was already described in IM V, bugs in the ROMs of older machines prevented this check from ever being done. Now, a quick fix: (make sure you have a backup of the whole disk!!!!!!) 1) This checksum check is only performed if (among other things) the partition type of the partition containing the driver starts with the letters "MACI" (case insignificant). 2) Find a program that allows you to edit the hard disk on a block level, bypassing SCSI dvivers (MacZap tools, SUM Tools, Apple's SEdit). 3) Look in block 0. There you will find the starting block and length of the driver as it is stored on the disk. Write this down. 4) Look at the first two bytes of block 1. These should contain the letters "PM", indicating a new type partition map (IM V pp. 578-) If they don't, the checksum stuff can't be the problem, you're out of luck with this fix. 5) In this new partition map, find the entry for the driver. Each entry occupies one block. You should for an entry with a type starting with the letters "MACI" and the same starting block as you have written down for your driver. The type description starts at offset 30 (decimal) and the partition's first block number is found at offset 8. 6) If you find this entry, change the 'M' in "MACI" to anything else but an "M". Write the changed block back to disk. 7) Try if the fixed worked by rebooting from the hard disk. Good luck, Dolf Dolf Starreveld Phone: +31 20 592 5056/+31 20 592 5022, TELEX: 10262 HEF NL EMAIL: dolf@fwi.uva.nl (dolf%fwi.uva.nl@hp4nl.nluug.nl) SNAIL: Dept. of Math. and Computing Science, University of Amsterdam, Kruislaan 409, NL-1098 SJ Amsterdam, The Netherlands