sysop@pro-generic.cts.com (Matthew Montano) (05/16/89)
stein@uconnvm.bitnet was talking about the task of getting the extra 1.x meg out of a 40 meg hard drive that was capable of 41.X megabytes. Apple discovered something very interesting in the process of writing the SCSI installer program on the Macintosh. In the early versions of HDInstall the program used SCSI calls to determine the largest size possible on it. As a result, some '20' meg harddrives were capable of holding sometimes upto 22 megabytes of data. Then some people were discovering that they could no longer restore their harddrive when they change computers. Some people had owned a Mac Plus with an external 20 meg drive and wanted to upgrade to a Mac SE with a 20 meg drive. The crunch came here in that Apple has changed the actual mechanism inside their 20 meg drives quite a few times and so that the Mac SE 20 meg harddrive might only be 20.2 meg, while the external was 21.9. The data to be restored couldn't be restored to the drive! (Back in the days of lousy backup/restore programs) so the data was lost. With multiple drive manufacturers out there, they came to a unique solution. The HDInstall program from Apple would format the drive to 20 megabytes, EXACTLY, no if's and's and but's about it. A 41.2 meg drive would be formated to EXACTLY 40 megs, likewise with larger sized drives. I'd assume that is what GS/OS and other HD format programs are doing, trying to follow this protocol to allow easy use of backups and restores. CMS and others take a different approach all together, in that the HD controller card only allows certain specific sizes and no matter what drive mechanism you connect to it, the card 'rounds' off sizes. Hope this helps "stein@uconnvm.bitnet" figure out why he couldn't get the extra meg or so on his harddrive. Matthew Montano ProLINE: root@pro-generic | UseNet: root@pro-generic.cts.com DDN: root@pro-generic%nosc.mil | UUCP: ...crash!pnet01!pro-generic!root pro-generic - Toronto, Ontario, CANADA - 416-237-0308, 3/12/24/9600 - PUBLIC ============================================================================== ProLine: sysop@pro-generic |DDN :crash!pnet01!pro-generic!sysop InterNet:sysop@pro-generic.cts.com|UUCP: hplabs!crash!pnet01!pro-generic!root ==============================================================================