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To: John Biddle who wrote (7366)	2/17/1998 11:46:00 PM
From: Stitch	Read Replies (1) \| Respond to of 9124

John, I am presuming, from IBM's and Fujitsu's predictions of second actuator models in two years, that there is only so much that can be done to speed up data transfer rates. For sure Ultra SCSI, 1394, and Fibre Channel along with higher rotational speeds, represent vast improvements but a second actuator goes a long way to improving rotational latency (presumably cutting it in half at least), greatly improving seek time. My question is whether or not those predictions include a second read/write channel in the drive or will both actuators seek from the same signal source? In any case, the drift of all this is to take advantage of greater bandwidth communications and a clear trend to more and more mission critical applications. Its a netcentric view, which IMO is a clear trend, that I happen to believe will be good for disk drive makers. Best, Stitch.

To: John Biddle who wrote (7366)	2/18/1998 8:43:00 AM
From: UpwardBound	Respond to of 9124

Re: dual actuators in disk drives John, In the case where an application needs double the throughput, there is such a thing as synchronized spindles. This had been applied for years at Seagate. I'm not sure if they are still doing it. What happens is two drives are synchronized and then the data is interleaved between the two, doubling the burst transfer rate. This of course requires a much modified controller, but at least the drives are basically off the shelf units (sync spindle is fairly simple to do) and there's no redundant hardware. If an application needs blazingly high speed, they have also built drives that have parallel read channels where they read from multiple heads simultaneously. Again, Seagate has also done this, but I can't say if it's still going on. At one point they were shipping an 8" product that offered 2 heads parallel and another version of that with 9 heads parallel (8 data bits with one parity). The 9 head parallel was a specialty product developed jointly with supercomputer manufacturer Cray. Very early in the disk drive industry I heard that IBM(?) had built a 14" product that had dual actuators but that did not last long. Also going way back, IBM also manufactured a 14" product (MMD) that had a large number of fixed heads on one side of a disk. (I think this product ended up being transferred to Control Data as part of the settlement of some sort of lawsuit.) This product had a PCB with something like 50 heads mounted on it and then a rotating disk that just sat on top. TPI was very low back then and thermal expansion was never an issue like it is today. That's why we have embedded servo. Probably more than you wanted to know. Anyway, since the things you are suggesting have been implemented in the past, you should be pleased to know that your ideas have merit. Take Care, --UpwardBound