3 ms·
Yes, also no contention for video memory access on the BBC.
by jlarcombe 6y ago
Yes, also no contention for video memory access on the BBC.
- beagle3 6y agoThe spectrum also had contention for video memory access; The memory map was: 0->16K: ROM 16K->32K: "Slower" RAM (ULA/Video has preference so may delay CPU) 32K->64K: "Faster" RAM (Same RAM, but nothing other than CPU accesses it)
- jlarcombe 6y agoYes - that's what I meant - sorry if not clear. BBC ran at full speed all the time (except when interfacing with 1Mhz peripherals). Spectrum clock speed higher but contention for video RAM. Also traditionally the 6502 is regarded as having greater throughout for same clock speed (something to do with the width of the ALU and the complexity of instruction decoding?)
- beagle3 6y agoFrom my experience (lost of Z80, much lesser 6502, but still some), it's mostly the indirect addressing modes - The Z80 had lousy IX/IY indexed access, and direct HL/DE/BC access. The 6502 had great indirect access through X and Y. So when manipulating memory (which is .. most of the time), The Z80 often needed 3-4 instructions for what the 6502 could do in one. The z80 had more registers and some 16-bit arithmetic.