It seems that the concensus here is that it is better to guess than to ask, so let me try

I have actually two MCU cores at home; the classic 8051 itself and the 8031 with is a romless one.
language lesson: they are Identical "cores" but different "derivatives". For these 2 chips you need do nothing different.

I did not metion what chip I want to use because I don't only want to decoder the memory addresses for only the 8051 chip but with either the Microcontroller or Microprocessor chip.
question: does "Microcontroller or Microprocessor" refer to the two above?

When we connect at least two EEPROMs or ROMs to a processor we need to select either that ROM or RAM chips without working with the other ROM or RAM chip(let say I want a memory map of 8k x 16 but I have on hand only 2k x 8 of chip memory RAM or ROM, now how to configure the hardware to choose to range on either the first two RAM or ROM chip or the last one?)
if we are talking about 8051 or 8031 there is no need to "select either the ROM or RAM" that is done by !RD and !PSEN

To use chips of identical size such as "only 2k x 8" you need an 1 of x decoder, such as a 1 of 4 decoder or 1 of 16 decoder, both are avilable as standard 74xx chips. Anyhow, why even do that, you can buy a 128*8 RAM for $3 and wiring up a lot of 2k RAMs will cost you way more.

Erik