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The only speed which needs to be in common is the PIO speed used for data and register access. This needs to be the lowest common denominator as determined by both the mode bit indicated and any derated cycle time indicated by either device's identify data. One can simply employ PIO mode 0 for register access and PIO data, since in most cases, 99% of the work will be done via DMA transfer. The DMA mode data transfer speed can be completely independent per device. I've not encountered any problems with data transfers using a DMA mode with any number of pairings of drives. I've not seen an instance of reasonably paired drives of similar generations having a problem running at different DMA data transfer speeds. Probably, there are some in the world which have a problem, since the world is full of misbehaving drives. Such drives are likely to have problems regardless of speed though. >This message is from the T13 list server. > > > >Regarding when you have two devices, with two different speeds, can I >use the fastest speed of the two to communicate with both of them ? > > >Stephane Cattaneo >Satellite division >STMicroelectronics -- --------------------- I make stuff go. --------------------- Larry Barras Apple Computer Inc. 1 Infinite Loop MS: 306-2TC Cupertino, CA 95014 (408) 974-3220
