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Unformatted text preview: ill have no more than a few megabytes of SRAM, but hundreds or thousands of megabytes of DRAM. Static RAM
SRAM stores each bit in a bistable memory cell. Each cell is implemented with a six-transistor circuit. This circuit has the property that it can stay indeﬁnitely in either of two different voltage conﬁgurations, or states. Any other state will be unstable—starting from there, the circuit will quickly move toward one of the stable states. Such a memory cell is analogous to the inverted pendulum illustrated in Figure 6.1. Unstable Stable Left . . Stable Right Figure 6.1: Inverted pendulum. Like an SRAM cell, the pendulum has only two stable conﬁgurations, or states. The pendulum is stable when it is tilted either all the way to the left, or all the way to the right. From any other position, the pendulum will fall to one side or the other. In principle, the pendulum could also remain balanced in a vertical position indeﬁnitely, but this state is metastable—the smallest disturbance would make it start to fal...
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- Spring '10
- The American