As we have expected, RocketRAID 1520 is really a dual-channel SerialATA150 RAID controller and RocketRAID 1540 is its four-channel counterpart. We only were not quite right about the analogy with the older models (sorry about it). Yes, RocketRAID 133 is a dual-channel ATA/133 RAID controller, and RocketRAID 404 is a four-channel one. However, we missed out one very important thing. Every channel of the parallel ATA interface allows connecting to it up to 2 HDDs, while each channel of the serial interface supports only one HDD. This way, RocketRAID 1520 controller is simply unable to support RAID 0+1 (stripe + mirror), while RocketRAID 133 does support it (RocketRAID 1540 supports RAID 0+1).

Both SerialATA controllers go with a special RocketHead100 converter:

As you can guess from the way it actually looks, it allows connecting HDDs with parallel ATA interface to SerialATA controllers. Unfortunately, we have no idea how many converters are included into the package. It seems pretty reasonable that RocketRAID 1520 should go with two of them, while RocketRAID 1540 – with 4 (corresponding to the number of HDDs they support). But, what will be in reality? Time will show...