Design and discuss the Stored program organization in computer system. Discuss the significance of mode bit w.r.t. to direct and indirect addressing. How many address bits a computer system with memory capacity of 4096 words with 16 bit instruction in each word takes. Draw the corresponding instruction format.
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Answer:
STORED PROGRAM ORGANIZATION: The simplest way to organize a computer is to have one processor register and instruction code format with two parts. The first part specifies the operation to be performed and the second specifies an address. The memory address tells the control where to find an operand in memory. This operand is read from memory and used as the data to be operated on together with the data stored in the processor register.
Instructions are stored in one section of memory and data in another. For a memory unit with 4096 words we need 12 bits to specify an address since 212 = 4096. If we store each instruction code in one 16-bit memory word, we have available four bits for the operation code (abbreviated op code) to specify one out of 16 possible operations, and 12 bits to specify the address of an operand. The control reads a 16-bit instruction from the program portion of memory. It uses the 12-bit address part of the instruction to read a 16-bit operand from the data portion of memory. It then executes the operation specified by the operation code.
