On Jun 17, 2009, at 10:14 AM, irrational john wrote:
> I'm basing that on what I read in this Wikipedia article which sounds > credible to me. > http://en.wikipedia.org/wiki/AT_Attachment#Cable_select As usual Wiki is Wiki. Take it or leave it, as you choose. The background for the CS, first, during device initialization, and M/ S, second, during normal device operations, as employed by Apple in the B&W and all later models, is ... US Patent 5761460 - Reconfigurable dual master IDE interface ... which patent "teaches" how an IDE interface may be utilized in a new and inventive way to: 1) determine if a cable is attached at all, 2) if a cable is attached, to determine which of 40-wire/40-pin or 80- wire/40-pin cable it is, 3) if a master device exists, to determine the fastest it is capable of being operated, 4) if a slave device exists, to determine the fastest it is capable of being operated, and, finally 5) given all of the above, the possible two semi-independent channels (on the one single bus) may be appropriately programmed for the best device utilization. Implicit in the above objectives, the devices themselves may interrogate the connector and its cable to determine how best to communicate with the host. In all of these discussions, the computer itself is the initiator (host), and the attached devices are responders (dependents whether master or slave doesn't matter as masters and slaves are actually "peers" of each other). For the particular case of modern optical drives, such as fast DVD burners, the burner needs to know if it can depend upon the host to ship data with high data integrity, and at a rate which will not cause the device to under-run (implicitly, a device cannot be over- run as the host is programmed to ensure this). So, the burners specifically look for the differences between the 40- wire/40-pin and the 80-wire/40-pin cable, and it limits the burn rate to 8X or less for the 40-wire/40-pin case, and possibly 20X or more (but surely more than 8X) for the 80-wire/40-pin case. From the patent text (abbreviated): ... SUMMARY OF THE INVENTION A dual-master data storage interface is disclosed which flexibly configures and connects data storage drives in the portable computer to optimize performance when the portable computer is operating in a stand-alone mode. The invention further optimizes accessibility to additional data storage drives when the portable computer is docked to an expansion unit. The interface has first and second channels adapted to control first and second data storage drives and registers for configuring each drive as a master drive or a slave drive. When the portable computer operates as a stand-alone unit (i.e., not docked to the expansion unit), each drive on the portable is configured to operate as a master drive which is separately connected to a channel to optimize performance. ... Upon separation, each drive on the portable computer is configured and remapped as a master on a separate channel for maximizing data transfer performance. Thus, by allowing for flexibility in changing the drive configuration and channel connection, the invention ensures compatibility with the standard BIOS when the portable computer is docked with the expansion unit. Further, the present invention optimizes data transfer performance from the drives when the portable computer is separated from the expansion unit. ... --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
