Hello PeterH! On Monday, 20th of July 2009, PeterH wrote: > On Jul 19, 2009, at 2:51 PM, Mac User #330250 wrote: > > Anyway, I used this script (to make things more easy): > > http://4thcode.blogspot.com/2007/12/using-128-gib-or-larger-ata- > > hard-drives.html > > From which I quote: > > > "Finally IOATAController::issueCommand in IOATAFamily-173.3.1/ > IOATAController.cpp splits an Extended LBA into two halves and sends > them one after the other. This shows that 48-bit addressing is just a > protocol extension designed to be compatible with older hardware". > > > Perhaps an oversimplification. > > A large drive EXPECTS two CDBs (command data buffers, logically a > "command control block" or data structure), but should it receive > just one, then it assumes the high order bits are all zeros, and then > the drive defaults the command to the first 131,072 MB. > > However, the drive also ACCEPTS two CDBs, in which case the first > provides the lower-order 24 bits while the second provides the higher- > order 24 bits. > > This is really an issue between the old, unmodified O.F., which can > only provide the first CDB and the new, modified O.F., which provides > both CDBs. > > The fact that the drives all seem to accept a single CDB, the first > one, and then to default to LBA24 mode, is indeed fortuitous. > > However, there is really no reason to artificially limit one's self > to LBA24 as the LBA48 properties can be added persistently (that is, > permanently, until the next "reset-nvram" O.F. command has been issued). > > For, if you NEVER issue the "reset-nvram" O.F. command, then your pre- > QS 2002 machine will ALWAYS have LBA48 enabled.
Quite right. Once the nvram has been altered the change is permanent, until you reset the non-volatile memory. The only issue I don't quite get is that the Mac OS X kernel extension doesn't overcome this limitation all by itself. The driver must know that this is only a device property problem and could therefor change it accordingly. Anyway, thanks for all the facts about this. I really appreciate it. And I'm happy that my pre-QS2002 now features LBA48 support and therefor drives >128 GB. I googled a lot and didn't find this workaround very easily. I'm not sure if that much people know about it. At least I found a lot of QS2002 related items on eBay that are advertised with >128 GB hard drive support. If you don't know why you will end up paying more without it really being necessary. A QS2001 would do as well and will be cheaper. Thanks, Mac User #330250 aka Andreas --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed Low End Mac's G3-5 List, a group for those using G3, G4, and G5 desktop Macs - with a particular focus on Power Macs. The list FAQ is at http://lowendmac.com/lists/g-list.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to g3-5-list@googlegroups.com To unsubscribe from this group, send email to g3-5-list-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/g3-5-list?hl=en Low End Mac RSS feed at feed://lowendmac.com/feed.xml -~----------~----~----~----~------~----~------~--~---
