CompuServe Messages

Chris, to understand this you have to understand something about the way the Amiga uses its memory chips. A part of the system is designated as Chip RAM and a part as Fast RAM. The Chip RAM is accessible to the CPU as well as the custom chips that give the Amiga its speedy graphics, sound, etc. The CPU and the custom chips split the amount of time that each has access to this bank of memory, with the CPU having one half the clock cycles and the custom chips the other half. Unless something comes along that requires heavy duty cycles for the custom chips, they can lock the CPU out if they need to, this is the rule. With Fast RAM, the custom chips can't touch it, so the CPU has access to it 100% of the time, unlike Chip RAM which it has only 50% of the time, or less. Now, let us say you add an accelerator that doesn't have any RAM of its own. True, you will get some measure of speed up due to the CPU have an instruction and data cache, but it will on be marginal at best. The CPU is still limited to the speed by which it access the Fast RAM and Chip RAM on the motherboard, which is not very fast at all. Basically, the CPU spends much of its time waiting around for the memory to get back to it with the information it needs, either instructions or data, to continue the task it is running. I'd guess about a 50% speed up when comparing an '030 to a 68000 and much less when comparing an '030 to an '020 (the main difference is that the '030 has a data cache), which probably won't be noticed by most users. On the other hand, if you add 32 bit high speed Fast RAM to the equation, things change markedly. Since the memory is operating at a much higher speed that either the Fast RAM or Chip RAM on the motherboard, it can do a better job of keeping the CPU in instructions and/or data since it is operating closer to the actual information requirements of the CPU. So, without the "Faster" RAM, you won't notice much if any improvement. Brian bjbart@watserv.ucr.edu