Final answer:
A 1 GHz microprocessor can execute a maximum of 20 million instructions per second when main memory has an access time of 50 ns and there is no cache, as each instruction takes 50 ns to be fetched and executed.
Step-by-step explanation:
To calculate the maximum number of instructions that can be processed in one second by a microprocessor with a clock speed of 1 GHz, we first need to understand that 1 GHz (gigahertz) means that the processor has a cycle rate of 1 billion cycles per second. Each cycle potentially represents one instruction execution. However, if main memory has an access time of 50 nanoseconds (ns), this means that each instruction requires 50 ns to be fetched from memory. Since there are 1,000,000,000 ns in one second, the processor is initially capable of executing 1,000,000,000 instructions per second at 1 GHz. But taking the memory access time into account, only 1 instruction can be executed every 50 ns.
Therefore, to find out how many instructions can be processed in one second when each instruction takes 50 ns, we perform the following calculation: 1,000,000,000 ns / 50 ns per instruction = 20 million instructions per second. This is the maximum number of instructions that can be processed in one second for the microprocessor.