DYNAMIC RANDOM ACCESS MEMORY

Figure 6-38.—Example of a MOS UV EPROM: A. Block diagram; B. Pin arrangement location are transmitted from the requestor (CPU or I/O sections) to the memory section. The computer’s internal bus system transmits the memory request or selection and location to the memory section. READ/WRITE MEMORY— In read/write memories, the data can be retrieved from memory, altered, and written back into memory. Read/write memories are random access memories. They are categorized according to the materials they are constructed from and not their basic operation. CORE MEMORY— Magnetic core storage is composed of hundreds of thousands of very small doughnut-shaped ferrite cores. The ferrite cores are strung together on grids of very thin wires known as core planes. Each core can store one binary bit 0 or 1) of data. A core is magnetized by current flow through the wires on which the core is strung. A core magnetized in one direction represents a binary zero, and when magnetized in the opposite direction, a binary one. The direction the core is magnetized is dependent on the direction of current flow through the wires on which it is strung. FILM MEMORY— Magnetic film storage is composed of hundreds of thousands of very small “I”- shaped magnetic thin film spots. Two paired thin film spots are used for each bit position. A film spot is magnetized by current flow through the word line or sense/digit line. A film spot magnetized in one direction represents a binary zero, and when magnetized in the opposite direction represents a binary one. SEMICONDUCTOR MEMORY— Semicon- ductor RAM refers to semiconductor IC memories that can be used in a read mode as well as a write mode. Semiconductor memories are normally nondestructive readout and volatile memories. RAM CHIP— RAM chips make up semiconductor RAM. They contain large numbers of memory cells and the logic to support them. Each memory cell is an electronic circuit that has a least two stable states. Each of the two-state memory cell circuits can store one bit (0 or 1). STATIC RANDOM ACCESS MEMORY (SRAM)— Static random access memories (SRAMs) are semiconductor integrated circuits that use a flip-flop application for each storage cell. The flip-flops are made of either bipolar or MOS transistors. DYNAMIC RANDOM ACCESS MEMORY (DRAM)— Dynamic random access memories (DRAMs) are semiconductor integrated circuits (ICs) 6-31