instructions from the next. It is done by holding machine instructions 'in different memory locations. The memory address and its contents are totally different the address is a particular location in memory and it contents an application, system program or it may be data.The computer's memory, both RAM and ROM are regarded as a contiguous list of locations. Each location is identified by its unique memory address. In fact, the memory is organised as a matrix of storage cells. For simplicity, we will take as an example of a matrix, 16 rows and 16 columns, providing 256 addressable locations or cells. Specifying its row and column co-ordinates can access any cell in the matrix. The memory chip circuitry has to translate any memory address into the corresponding co-ordinates.For example, the CPU requests access to address 227 (i.e. 11100011 in binary. This binary pattern is placed on the address bus. The four least significant bits (0011) are used by the column decoder to determine the column co-ordinate, known as the Column Address Select (CAS) line. The four most significant bits (1110) are used by the row decoder to determine the row co-ordinate, known as the Row Address Select (RAS) line. The row and column address lines then access only the single unique cell, which corresponds to the address supplied. Note that the convention is to number address bus lines and data bus lines commencing with line 0. So, a 16-bit address bus would number its lines from AO to A15 and an 8-bit data bus would number from DO to D7. As can be seen, any cell in the matrix can be individually accessed. Hence the description as a random access device. The cells accessed may contain a program instruction or program data. The circuitry can't distinguish between instructions and data and the programmer has to ensure that the correct addresses are being accessed.The term Memory Access Speed means that how long it takes the memory in nano-seconds to retriev...
