CompuServe Messages

John, Yup…it is very expensive to have all heads write at once. Among other things…the whole logic of how a drive works and stores data would have to change. Among the changes needed, absolute syncronization of the heads is required, the amount of circuitry needed goes up by a factor of 8 or more and so forth. Error correction becomes harder as does handling defects in the media itself. As an example, we've got some commerical drives at work that use multiple heads at once. It's done by having two complete sets of heads. Reads or writes are alternated between the sets of heads…thus it's possible to do 2 reads or 2 writes at any one time. The drives hold 500 Megabytes of data and cost $25,000 apiece. Compare that with a consumer type of 500 MB drive that costs in the $1,000 price range. What more heads does for you in a consumer type drive is give you several things: 1. You can write more data without stepping the heads. Timewise, stepping the heads is a relatively expensive operation when compared with simply switching from one head to another. 2. You can store more data in the same size package…because more heads means more surfaces (platters) that can be used. 3. Economies of scale…the same basic circuitry is needed for a 2 headed drive and a 6 headed drive. All that really needs to be added are the additional platters and heads and perhaps a slight bit more switching circuitry. Don