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. --~--~---------~--~----~------------~-------~--~----~ 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 [email protected] To unsubscribe from this group, send email to [email protected] 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 -~----------~----~----~----~------~----~------~--~---
