stepping machanism of Apple Disk ][ drive (was Re: Heatkit 51/4 floppies)

From: Allison J Parent <allisonp_at_world.std.com>
Date: Sun Apr 11 13:37:23 1999

<> The point was apparently missed. Of course I can take a cmos z80 and
<blow
<> that out of the water using a 6 or 8 mhz clock.
<
<But because of the way the phases are used, a 2MHz 6502/65C02 is running a
<roughly the same rate (for comparable operations) as a 4MHz Z80.

Yes, the 6502 overlaps the instuction fetch and execute (mini pipeline).
The z80 is more classic multi-state machine. In the end the two parts are
roughly the same speed for their generation. IE: a 4mhz z80 does basic
operations in 1uS and 6502 at 2mhz is about the same. the difference is
any is when complex indexing or other tassks are discussed where the z80
has a better instuction set (though slower...more states) the 6502 uses
more small instructions(fast but many). In the end they do the same task
just different.

That supports the only logical conclusion... clock speeds dont count.
The full measure is instruction execution time. Which is why I used the
PDP-8 example as that machine used 1.4uS core yet it had a fairly high
effective speed.

Now to extend this to other older cpus there are some out there that were
just plain slow or due to their instruction set so awkward as to end up
being slow.


Allison
Received on Sun Apr 11 1999 - 13:37:23 BST