Mr Macaw wrote:
On Tue, 31 May 2016 21:12:37 +0100, wrote:

On Tue, 31 May 2016 19:10:05 +0100, "Mr Macaw" wrote:

The CPU itself has 4 or more seperate cores independent of one
another.

You also have to look at data paths, access to DASD, access to RAM
and how the firmware/software is written.

The point is two or more things can easily be happening
simultaneously. One CPU core is doing a calculation, while the other
is loading from memory. Same is true of the brain.
If what you said was true, then I couldn't run 4 programs at the same
time maxing out all 4 cores, with all of them running the same speed
as if they were run individually.

Time was - maybe still - there were instructions to enable/disable
interrupts. A CPU can only do one thing; it can SEEM to do multiple things
because it pauses what it is doing (interrupts) to go do something else.
That is totally transparent to the user because of the speed at which things
are done. Even 45 years ago when CPU speed was around 1/1000 of the current
speeds, the CPU was processing 100,000 instructions per second.

It was sometimes necessary to disable interrupts; one I recall was for
floppy disc read/write.