10. New Developments in Electronic Memories

The versatile capabilities that have made the computer the great success of our age are due to exploitation of the high speed of electronic computation by means of stored programs. Once prepared, a program can be reused any number of times which involves remembering and recalling, for which high speed is worthwhile in the first place. Storage devices or memories must have capacities sufficient not only for intermediate results but for the input and output data and the programs.

Computers can “remember” and “recall”, and virtually unlimited is the capacity of computers to remember (to store digital information). Associated with the capacity of remembering is the capacity of recalling.

Access time is simply the time it takes to read or write at any storage location. The cycle time is the specified minimum period to complete read and write operations. The data-transfer rate is the rate at which information is transferred to or from sequential storage positions.

Random access memory is considered “random access” because you can access any memory cell directly if you know the row and column that interest at that cell. Serial access memory stores data as a series of memory cells that can only be accessed sequentially. If the data is not in the current location, each memory cell is checked until the needed data is found.

HP announced dramatic new breakthrough in molecular electronics. The bit density of the device is more than 10 times greater than today’s silicon memory chips. For the first time, they combined both memory and logic using rewritable non-volatile molecular-switch devices and fabricated the circuits using an advanced system of manufacturing called nano-imprint lithography. (14)

One of the first electronic memories was a circulating delay line a signal transmission device in which the output, properly amplified and shaped, was fed back into the input. Although it was economical it had the inherent drawback of serial access: the greater the capacity, the longer the average access time. The first random-access memories were electrostatic storage tubes.

The core memory has become the main internal computer memory and was used universally until challenged by semiconductor memories. The core memory has also been extended to very large capacities, of the order of 100 million words.

Modern computers have significantly more memory than the first PC’s of the early 1980’s, and this has had an effect on development of the PC’s architecture. With a large amount of memory, the difference in time between a register access and a memory access is very great, and this has resulted in extra layers of “cache” in the storage hierarchy.

Main memory is attached to the processor via its address and data buses. The width of the address bus dictates how many different memory locations can be accessed and the width of the data bus how much information is stored at each location. Every time a bit is added to the width of the address bus, the address range doubles.

By early 2002’s, it should be clear whether the technology can be scaled down enough to make it feasible and whether the magnetic material can be worked into traditional chipmaking processes. The technology could represent e serious threat to the various silicon-based memory chips towards 2010. (26)