Posted By
JamesD
on 2016-09-22
15:20:08
|  Re: What would I do differently in the Plus/4
gerliczer is correct on the Z80.
There can be up to 4 t-states per memory access.
Part of the reason earlier Z-80 machines only run at 1.5-2 MHz is due to the RAM speed of the day.
The TRS-80 Model I can easily be sped up if you drop in faster DRAMs. The later Model III came from the factory running at the higher speed.
The MSX hardware created additional wait states so it could use cheap DRAMs.
The BBC Micro ran at 2MHz. They added coprocessor boards later with their own RAM at higher speeds, but it's not the same as the main CPU being clocked faster.
The Apple IIc Plus had a higher clock speed, but it achieved it with SRAM cache. Main memory was still slow. And that machine came out in 1988!
*edit*
SRAM doesn't require cycles to be used for refresh, so they are faster that way. I don't know about faster SRAMs coming out before DRAMs though.
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