English Amiga Board - View Single Post - 68020 performance on an A500 and bad magazine articles

AestheticDebris · 12 February 2024, 23:32

I suspect the author just didn't understand 680x0 architecture. He's assuming (incorrectly) the the 68000 was entirely 16-bit and thus optimal when hooked up to a 16-bit bus, whereas the 020 is 32-bit and must therefore be having to double access memory each time it reads because of the 16-bit bus.

This might be true on some architectures, but 680x0 doesn't really work like that. Logically it's designed like a 32-bit CPU, it just accesses things in 8, 16 or 32 bit chunks depending on the bus size available. Now it's certainly true to say a 68020 isn't running at full speed when accessing 16-bit memory, but that doesn't make it slower than a 68000, just slower than a 68020 with a 32-bit bus.

12 February 2024, 23:32	#6
AestheticDebris Registered User Join Date: May 2023 Location: Norwich Posts: 412	I suspect the author just didn't understand 680x0 architecture. He's assuming (incorrectly) the the 68000 was entirely 16-bit and thus optimal when hooked up to a 16-bit bus, whereas the 020 is 32-bit and must therefore be having to double access memory each time it reads because of the 16-bit bus. This might be true on some architectures, but 680x0 doesn't really work like that. Logically it's designed like a 32-bit CPU, it just accesses things in 8, 16 or 32 bit chunks depending on the bus size available. Now it's certainly true to say a 68020 isn't running at full speed when accessing 16-bit memory, but that doesn't make it slower than a 68000, just slower than a 68020 with a 32-bit bus.