Difference between Fast memory & Z3 Fast memory?

[divined]

Hello everybody

The subject title is pretty self explanatory. I ran into this while trying to install AmigaOS 3.9 on WinUAE. The fast memory option could only be set up to 8MB, while the Z3 Fast memory could go much higher!

George Papadopoulos

[Piru]

Fast memory is within 24bit memory space (the only space for 68000, 68010 and 68ec020). The area 0x200000 -> 0xa00000 is reserved for the memory in the memory map, thus maximum 8MB.

Z3 memory is mapped to 32bit memory area and thus is not limited in this way.

For WinUAE there is no difference except that the address of the memory (and that 68000, 68010 and 68ec020 can't have Z3 mem). Since it's emulation, both memory is equally fast. However, some rare apps might require memory at 0x200000 onwards, and with these you need to add some "Fast Memory", even if you have "Z3 Memory" set already.

[amigadave]

The other answer pretty much covered what I think you were looking for, but on real Classic Amigas that have accellerator cards, there is yet another type of, lets call it "Fastest" memory that is built-in on the accelerator card itself and has a faster direct bus to the CPU, eliminating the limits of the Zorro II or Zorro III buses transfer speeds.  Just a little extra info for your digestion.

[divined]

Nonetheless, I thought that the 68020 was a 32-bit CPU. Why can`t it access a 32-bit memory address space?

[patrik]

@divined:

The 68020 is a 32-bit cpu, but the cost-reduced 68ec020 variant only has 24 external address-lines, just like the 68000 and for that reason that variant only has an address-space of 16MB.


/Patrik