TABLE OF CONTENTS Memory can be classified into two types: read only memory and random access memory. Read only memory was discussed in chapter 9. Random Access Memory (RAM), or read/write memory, can be read and written at any time. There are no restrictions for writing the data into RAM. The two types of RAM are described below.
SRAM consists mostly of flip flops that store the binary information. The stored information remains valid as long as power is applied to the unit.
When compared with dynamic RAM (see section 10.2), SRAM is easier to use. It has shorter read and write cycles, can be constructed both in TTL and MOSFET technologies, and uses conventional storage devices like flip flops, whereas dynamic RAM requires charging or discharging capacitances.
This type of RAM uses unconventional memory storage devices. Logic levels are preserved as a charge, or an absence thereof, on capacitances. The primary advantage of this technology is that more data can be stored in a small area. Another advantage is that it consumes less power than SRAM. The drawback to dynamic RAM is that the circuitry weakens over time and will lose its charge. Therefore, it must be refreshed periodically. Dynamic RAM is available only in MOSFET circuits.
A CCD is a type of dynamic memory in which packets of charge are continuously transferred from one MOS device to another. CCD memory is inherently serial. In practice, memories are constructed...
