14 Nov
2005
14 Nov
'05
7:33 p.m.
woodelf wrote:
...
Having got a new PC ... 2 GHZ??? who knows the real
speed.
I have tried Spare time gizmos - pdp 8 emulator ( A minor bug
-- with windows how do you get the bell to sound ?).
I was running some sort of diagnostics and had the RTC displayed
and for about 10 minutes of real time, the clock advanced a hour.
That must be at least 6x faster than the real thing on this computer.
If a 2 GHz (give or take) x86 CPU emulates a pdp 8 at 6x, it means either the
code is inefficient, or the code contains a speed regulator that doesn't work
properly.
The original PDP-8 took 10 clocks at 1 MHz to execute one instruction, a 2 GHz
CPU has 20 million cycles to interpret one instruction. So at 6x realtime, the
program is using 3.2 million cycles to interpret one instruction.
Most likely speed and efficiency weren't goals of the emulator, so I bring this
up not to discredit the program's author but rather to say: don't use that data
point as anything but a lower limit on what kind of horsepower it would take to
use a micro to emulate a PDP-8. I imagine an AVR device at 20-40 MHz should be
able to emulate a PDP-8 at real time.