
Modern computer use multiple kinds of memory.

There is CPU registers, CPU cash , intern memory and extern memory.

If the CPU wants to read/write to memory.
It have to do it whit different speed to different kinds of memory.

CPU registers are fast.
and extern memory is slowest.

Data moves between this kinds of memory as blocks of data.

Between CPU registers and CPU cash in 16,32 or 64 bit blocks.

Between CPU cash and intern memory in 16,32 or 64 bit blocks.

Between intern memory and extern memory in memory pages (4096 bytes) blocks.

Given this a strategy for optimisation could be that we try to minimise 
the number of times a block get moved from one kind of memory to another.

To demonstrate and to test optimisers I have made the following 3 programs.

The all solve the same problem but are using memory on 3 different ways.
So a good optimiser should make them all run equal fast.

The problem is to take a big array of numbers and then accumulate 4 numbers
min, max, sum and product.

testA is the fast version.
It accumulate all values in one parse.

testB is slower
It accumulate all values in 4 parses.

testC is slowest.
It also accumulate the values in 4 parses.
But it don't start at element 0 and go to element n-1 but it jumps around 
in the array.