Modern CPUs have hundreds of megabytes of cache. That's more than the entire hard disk space required by Windows in the 1990s.
You could install an entire Windows system, emulated in cache of a modern CPU, including the hard disk, and modern computers are still slow, partly because the CPU does nothing while waiting for RAM to fetch data, and partly because decades of people prioritizing abstractions over efficient coding have made software totally inefficient.
You could install an entire Windows system, emulated in cache of a modern CPU, including the hard disk, and modern computers are still slow, partly because the CPU does nothing while waiting for RAM to fetch data, and partly because decades of people prioritizing abstractions over efficient coding have made software totally inefficient.