14 Nov
2005
14 Nov
'05
8:01 p.m.
Doing some math, 2GHz/100KHz is 2000MHz/0.1MHz or 20,000. At 6X the
cycle count is then 20K/6 = 3333 (not 3.3M).
One would think it takes well less than 3000 X86 instructions to emulate
a PDP-8 instruction (assuming one instr per clock).
Jim Battle wrote:
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.