In the previous section, the, recent innovations relating to the processing aspects of computer technology were discussed briefly. In considering some of the advances in devices for digital information storage, it may be stated that most of the primary storage incomputers is now supplied by semi-conductor circuits. There have been significant developments in memory technology affecting three areas of performance spectrum; the high speed, high performance; the midrange and the low speed bulk memory systems. It is now possible that even a small computer system might have cache memory, a small associative memory retaining most recently referenced information and in a readily available place.
In some cases, cache memory may be at the top of a hierarchy of memories having a wide variety of characteristics. Memory management, dynamic memory allocation, and virtual memory schemes, generally found in large computer systems, are now appearing on computers which are small and less costly.
The development of charge coupled devices (CCDs) and bubble memories has filled the gap which previously existed in the continuum of memory devices such as fixed-head magnetic disks and these are slower than other semi-conductor memories. These memories have advantage over magnetic disks in that they contain' no mechanical parts and could be used to store significant amount of information and can be treated as a structured file system.