Reproducing old machines with newer technology

If you?re talking about switching a single resource (or fixed set of resources) among consumers, the answer doesn?t directly tie to the technical approach used but rather to the efficiency of switching among consumers. For example, a multiprogramming OS has to do a context switch. That may require one or two instructions, which may be very fast (CDC 6600 ? about 3.5 microseconds) or not so fast (VAX). Or it may take a few hundred instructions (most machines). But you may also find more limited sharing systems where the switching is so fast that it isn?t a factor in the performance. The timesharing of the PPU logic in a CDC 6600 is an example: the logic is that of a 10 MHz class machine, but the memory is 1 MHz, so 10x sharing of the logic among 10 memory banks and 10 sets of state makes sense. That approach still exists; nowadays it?s called ?hardware threads (as in the mutithreaded MIPS processors from Sibyte/Broadcom and Raza/Broadcom and others) or ?hyperthreading?. But, as with so many things, Cray did it first. paul