Amiga 68k cpu

[Promilus]

@roondar - on-board fast ram would still be tuned to on-board CPU. Once you remove it and get even faster one with turbo that "fast ram" would become PITA to handle (fast fast RAM on turbo, fast ram on board and chip ram on board). IIRC A4k design shows how messy it is. And smarter choice would be dedicated slot for turbo - but that one assumes such expansion capabilities - which were not taken into account on A500 (but it actually has side expansion which can work that way ... that's how ACA works) and absolutely impossible on A600.

[roondar]

Originally Posted by Promilus

@roondar - on-board fast ram would still be tuned to on-board CPU. Once you remove it and get even faster one with turbo that "fast ram" would become PITA to handle (fast fast RAM on turbo, fast ram on board and chip ram on board). IIRC A4k design shows how messy it is. And smarter choice would be dedicated slot for turbo - but that one assumes such expansion capabilities - which were not taken into account on A500 (but it actually has side expansion which can work that way ... that's how ACA works) and absolutely impossible on A600.

Yeah, I did think along those lines, but I'm not a HW guy so I try to be careful when I start talking about what can/can't be done easily. Thanks for the extra info

[sandruzzo]

Originally Posted by roondar

Adding a small amount of Fast RAM tot the design is something that on paper sounds like it makes a lot of sense. But despite me not being a hardware guy (so I have no idea how to make that work), it seems to me it's not actually trivial to do this and still allow a Fast RAM/CPU slot on the side of the machine as we have now.

The way I understand it you can't just randomly make an extra bus and those pins have to be connected somehow. So it sounds to me like you'd need potentially expensive bus arbitration.

Of course, I know nothing about hardware, so maybe I'm wrong

Ah, I see. I'm no HW guy, but my guess it that this wouldn't have been so easy to do back in 1983/1984. You got to remember, when the Amiga was first released, it was actually really quite fast as far as consumer hardware went. The 7MHz 68000 was a massive upgrade compared to 8 bit systems and it ran circles around the common 8088 based XT's. It competed favourably with 286 based systems (certainly in terms of GFX abilities) at a much lower cost.

My problem probably is that I just don't see the Amiga as being too slow or poorly designed when you place it in it's time frame

I remember some 68k accelerators for A500 with little fastram, doing their jobs with no problem at all.

[roondar]

Originally Posted by sandruzzo

I remember some 68k accelerators for A500 with little fastram, doing their jobs with no problem at all.

So do I. And they tended to be rather expensive for what they were and usually had incompatibilities or other limitations that limited their performance gains to far less than what you might expect. Which goes hand in hand with what I said above.

The point I made isn't to say it couldn't have been done, the point is that there's a reason it wasn't. Reading up on things like the AdSpeed shows to me that merely adding a tiny bit of Fast RAM would not have achieved much, if at all for speed, while costing quite a bit to implement in a useful way. IMHO, if you were to redesign the system to be based on Fast RAM, it would've been much better to make all RAM expansions true Fast RAM (perhaps even ditching the trap door RAM entirely or making that Chip RAM expansion space only). Sure, you'd still only get a minor speed boost, but it would have made things much better going forward.

[sandruzzo]

Originally Posted by roondar

So do I. And they tended to be rather expensive for what they were and usually had incompatibilities or other limitations that limited their performance gains to far less than what you might expect. Which goes hand in hand with what I said above.

The point I made isn't to say it couldn't have been done, the point is that there's a reason it wasn't. Reading up on things like the AdSpeed shows to me that merely adding a tiny bit of Fast RAM would not have achieved much, if at all for speed, while costing quite a bit to implement in a useful way. IMHO, if you were to redesign the system to be based on Fast RAM, it would've been much better to make all RAM expansions true Fast RAM (perhaps even ditching the trap door RAM entirely or making that Chip RAM expansion space only). Sure, you'd still only get a minor speed boost, but it would have made things much better going forward.

Things could have been done during actual Amigas' development. I mean buses were there. It seems to me that Amiga could have been better with a little more development time

[Daedalus]

Originally Posted by sandruzzo

Things could have been done during actual Amigas' development. I mean buses were there. It seems to me that Amiga could have been better with a little more development time

The A500 was designed to be as cheap as possible though, and was very long in the tooth when it was still being sold. Having extra logic for handling faster RAM and CPU was deliberately not included, instead the expansion port allowed for such logic to be easily added later on. Want an asynchronous CPU with its own optimised fast RAM? No problem, just add the necessary logic yourself. And there are many examples of expansions that do just that.