Step 17: Chip mem / fast mem

On Amiga, the memory is divided into different type.

Chip ram memory

This is the most common memory type. The memory is shared by CPU and chipset. If you want to setup a copperlist, then it must be in CHIP ram. If you want to do a blitter transfer, datas need to be in chip ram. If you want to play audio then data need to be in chip ram.
On original A500 OCS (Original ChipSets), there is 512MB of chipram. This is the total memory you have when you buy an Amiga 500. This quantity vary on others amiga model, but for now let’s focus on A500. (we will see later A600 and A1200).

Here are the chips of RAM memory (on left)

Fast ram

On A500 you can add some « Fast ram ». Usually it is an extension of 512KB of fast ram. Most of the A500 were equiped with this kind of extension. Games were running fine with 512MB but some have more feature when 1MB in total was detected.
Fast ram is only accessible by the CPU. The access are not slowed down if chip ram is also access in the same time. That’s why it is called « Fast ram » but the speed is the same as chip ram (so it is also called « pseudo fast ram » or « fake fast ram »). All the code, tables should be stored in there.

You can find these as small extension that you plug under you Amiga, using the trap made for this (the ram can also be called « trap-door RAM »)

Links:
https://en.wikipedia.org/wiki/Amiga_Chip_RAM

Demo of that time

megademo 8 by Kefrens

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