4.4 Memory Devices and Systems
Random-access memories can be both read and written. They are called random access because, unlike magnetic disks, addresses can be read in any order. Most bulk memory in modern systems is dynamic RAM (DRAM). DRAM is very dense; it does, however, require that its values be refreshed periodically because the values inside the memory cells decay over time.
Basic DRAM organization
Although the basic organization of memories is simple, a number of variations exist that provide different trade-offs [Cup01]. As shown in Figure 4.17, a simple memory is organized as a two-dimensional array. Assume for the moment that the memory is accessed one bit at a time. The address for that bit is split into two sections: row and ...