Accelerator without ram performance.

[CBH]

Cache is effectively fastram wired directly to the CPU. They can work both as fast as each other.

If you have sidecar fastram and a cpu socket turbo board, the cpu must talk to the fastram through the Amiga500 bus, which is working at a much slower speed. So performance chokes.

It's like if you have 10 lane 70mph highway and then make it all go over a one-lane stone arch bridge with traffic lights. Big bottleneck.

[CBH]

I know, but why Supra is that much faster? I t doesn't have ram, ram is in sidecar and CPU is 68000, biggest difference to Terrible Fire 520 is tiny 16kb data cache.

I literally just told you why, right in the very first sentence.

Cache is ram. More importantly, it is ram which is directly connected to the CPU, there's no motherboard bus bottleneck between the two.

So obviously performance is better because it has direct access to 16kb of high speed ram here. 16kb is a very respectable size cache for a late 80s system.

This is the whole point of cache. Every system where CPU's access to main ram is slow uses cache for this. Including your modern day PC.

[CBH]

Yes you did. Sorry. Cache seems to make huge difference even if ram is in side car. Wich is somewhat weird.

it's not weird at all.

every time your 020 board communicates with sidecar ram, it must do so over the Amiga 500 motherboard CPU bus, which is working only at the speed a 7mhz 68000 expects.

You can have a 200mph Ferrari, but if the speed limit on the road is 20mph, you won't get to the supermarket any faster than a lada.

Cache is a private race track for your Ferrari, you can go as fast as you want there.