Static RAM (SRAM)

word, it would take two 4K by 16 chips to provide 4,096 addresses of 32 bits each. To illustrate the random access nature of RAM, the number of words or addresses, and bits per word, we offer a simple illustration. Figure 6-26 shows the organization of a 64-bit memory. The 64 squares (mostly blank) in the figure represent the 64 positions that can be filled with data. Notice that the 64 bits are organized into 16 groups called words. Each word contains four bits of information. This memory is said to be organized as a 16 × 4 memory. That is, it contains 16 words, and each word is 4 bits long. The total number and capabilities (16 by 4 and so forth) of these individual circuits will define the total memory capacities of the respective computer. In our example, the total number of memory cells is 64. There are many variations in the ways a 64-bit memory could be organized: 64 × 1, 32 × 2, or 8 × 8. The memory in figure 6-26 looks very much like a truth table on a scratch pad. On the table afterword 3, you’ll notice the contents of word 3 is (0110). We say we have stored, or written, a word into the memory; this is the write operation. To look at the contents of word 3, we simply read the contents of word 3 using the read operation. What is also important about RAM memory is that we can read or write into any word on the table and in any order, that is why it is called random access. Figure 6-26.—Organization of a 64-bit memory. Static RAM (SRAM) Static random access memories (SRAMs) are semiconductor integrated circuits that use a flip-flop application for each storage cell. Figure 6-27 illustrates Figure 6-27.—SRAM cell and associated circuitry. 6-22