Logic per Track Devices

Publisher Summary In the past five years, the cost of a small solid-state signal switch has gone down by more than a factor of 10, while the mean time among failures has gone up at least by the same amount. A few innovations in computing systems have, however, resulted. This chapter describes a system that could not exist and would not even be worth thinking about (because many are needed) in the absence of cheap highly reliable electronic parts. Head per track disks are now state-of-the-art. The available units have a preamplifier associated with each head and share postamplifiers to a greater or lesser degree for two reasons: they are expensive and there is no need in most systems for transfer rates beyond those that can be achieved with a small number of postamplifiers. The cost of random access memory (primary computer storage) has not been going down as rapidly as most buyers would wish, and there is within sight no technique for making a primary memory that would achieve an order of magnitude cost reduction. Speeds are increasing (thin films and semiconductors), but applications that require the quantity of storage still suffer in performance as a result of the necessity for frequent transfer between primary and secondary storage. Therefore, it makes sense to consider systems that achieve high performance on file-oriented problems by combining the cheap high-capacity storage provided by rotating devices linked appropriately to a significant number of small signal switches. This chapter describes a system that associates with every track or pair of tracks on a disk between one hundred and a few thousand transistors.