The following question has been asked in the last three papers for 6 points:
"One might think that given the performance advantages of RISC technology, RISC machines would have eliminated CISC machines in the marketplace. Why has this not happened?"
Now, my answer would reference Stallings p.478 and be:
"There is a definite realization that both RISC and CISC designs can benefit from each other by incorporating each others features". Then, my understand is that RISC will never eliminate CISC, instead it might be the case that a new design which merge the better features of both will replace both CISC and RISC.
Please validate my answer for this question or tell me that I am missing the plot. Is this worth 6 points?
Another answer I got for an solution, don't know from where, probably WikiStudent, are:
Problem of backward compatibility.
Companies have invested billions of dolloars in software so this would be lost.
Intel has been able to employ the same ideas even in CICS architecture. Starting with the 486, the Intel's CPUs contain a RISC core that executes the simples (and typically most common) instructions in a single data path cycle, while interpreting the more complicated instructions in the usual CISC way. The net result is that common instructions are fast and less common instructions are slow. While this hybrid approach is not as fast as pure RISC design, it gives competitive overall performance while sill allowing old software to run unmodified.