Ah okay, thanks. Makes sense, you're not emulating a HD20, just serving a HFS file system.
I guess that means that it isn't possible to restore a CHD to a real Apple hard drive, or the opposite? What if some crazy person decided to use CHDman to dump an old Mac SCSI drive? Wouldn't it read 532 bytes/sector then?
Not at all. I *am* emulating an HD20 - SCSI harddisks in MAME and MESS always identify as one of the 2 model strings allowed for the HD20. And I have successfully booted raw CHDMAN dumps from several physical Macs on the emulation.
I'm not sure how to explain this better than my previous post, but I'll try again. The "system data" Apple cites is used by the microcontroller inside the drive to track where sectors are and such. There is no way for anything outside of the drive (ie, the Mac, or if you hook it up to a PC or whatever to dump it) to ever see that data or even know that it exists. The Mac sees the HDD only as however many 512 byte sectors. It cannot and will never see the system data.
Put in floppy disk terms, when you request that the OS pull sectors off the floppy you don't want the address marks and index bits and crap, you just want the data. The HDD's microcontroller enforces that: you can only ever see the data.
Last edited by R. Belmont; 10/28/09 10:50 PM.