Basic Properties of RAMs (Random Access Memories)

Abstract

As of 1988 there were fourteen generically different kinds of digital electronic memories in use (Fig. 2.1a). These ranged from the slow but cheap and highdensity disks for archival storage, to the fast Static RAMs (SRAMs). It was anticipated [53] that the memory market would simplify greatly over the years 1988–98 by the introduction of ferroelectric NonVolatile (NV) RAMs, eliminating core, magnetic bubble memory, and other devices (Fig. 2.1b). The aim of this chapter is to review that development and its present status. In the 1980s much of the motivation (and funding) for the development of ferroelectric NV-RAMs came from the US military. The reasons are illustrated rather graphically in Fig. 2.2. As shown, a typical military aircraft has 96 kbit of EEPROM in its embedded radar warning receivers, 8 Mbit of EEPROM or bubble memory in its removable cockpit recorder, 96 kbit of EEPROM in its electronic counter-measures (and counter-counter measures) receivers, 36 Mbit of SRAM or EEPROM in its main mission computer, 48 kbit in its EEPROM missile memory, and another 200 Mbit of bubble memory or EEPROM for its flight incident recorder and secondary memory. However, by 1999, this impetus has decreased dramatically. The US military has ‘no enemies’ with radiation-producing weapons requiring radiation-hard memories in its military aircraft; and the interest in ferroelectric RAMs has shifted strongly to the commercial sector (including commercial satellites).