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How Fast is My Chess
Computer's"Brain"?
By Larry Kaufman, I.M
When
purchasing a chess computer, many people want to
know how fast is its processor (a.k.a. "chip" or "C.P.U.").
Of course this is only one factor in determining
playing strength, along with RAM size, ROM size, and
program quality, but it is a legitimate question.
Unfortunately it is apt to be answered by quoting
the Megahertz, which is only a meaningful number
when comparing identical processors. A 16 MHz chip
performs 16 million clock cycles per second, but
different chips require widely differing numbers of
cycles to execute one instruction, Therefore MHz is
only useful for calculating the true speed of the
processor and is not a measure of speed by itself. I
think the reason that is widely used in advertising
is that MHz is a clearly defined, non controversial
number whereas more meaningful speed measures are
not universally accepted. Nevertheless, we must try.
I would like to introduce here the notion of "MaxMips".
The idea for this article and much of the data come
from Ron Nelson, Fidelity's hardware designer. "Mips"
stands for Million of Instructions Per Second,
while "MaxMips" refers to the highest possible value
of Mips. The point is that the Mips value for a
processor depends greatly on the nature of the
program. Ideally we should quote average Mips, but
this is a poorly defined quantity. MaxMip should be
simple to calculate, dividing the MHz by the minimum
number of clock cycles per instruction, although for
the more expensive processors there are
complications that make this calculation a bit
fuzzy. Bear in mind that some processors, may come
much closer to MaxMips on average than others, so
Maxchips is only a guide, but at least, unlike MHz,
it is a useful number to consider.
Let's
start with the 6502 chip, used in most of the models
over $100.00 until recently. It takes two cycles to
do anything, so a 5 MHz model like Fidelity Chesster,
Saitek Corona, or Mephisto Milano would have a
maximum speed of 2.5 Mips. A 6 MHz model like Novag
Super Expert C or Fidelity Designer 2100 display
would do 3 MaxMips. A Polgar 10 MHz would do 5.
Fidelity´s "Little Chesster", which uses a "single
chip" version of the 6502, does 1 MaxMip. For the
h-8 chip, the situation is similar - divide by 2.
The 10 MHz chip used in Fidelity Travel Master and
Saitek Blitz and Prisma does 5 MaxMips. Actually it
is considered to be slightly slower than the 6502 on
average, but not enough to worry about. Thus it can
be seen that it is only the limited memory in these
models that prevents them from achieving master
status.
A
popular chip for models in the $100 ballpark is the
single chip 6301. It takes 4 cycles to accomplish
anything, so the MHz must be divided by 4. Thus, the
8 MHz Novag Primo, Mephisto Marco Polo, and Fidelity
"USCF Academy" do 2 MaxMips, the Novag Super VI.P.
(9.8 MHz) does 2.45, and the Novag Beluga and Super
Novag (each 16 MHz) do 4. These numbers somewhat
overstate the true speed of the chip, the difference
between average and MaxMips being unusually large in
this case. As with the H-8, the small memory in some
of these models limits the strength more than the
processor speed.
Some examples of
MaxMips in low priced models are: Fidelity EI Dorado
0.4, fidelity Microchess 0.5, Novag Uno 0.53, and
Fidelity Marauder 1 MaxMip. They use a variety of
single chip processors. Now we come to the Motorola
68000 family. For the 68000, no less than 5 cycles
are required per instruction. so a 12 MHz machine
like the Mephisto 16 Bit Lyon or Vancouver does only
2.4 MaxMips, about the same as the much cheaper 8
bit models like Chesster, Corona, and Milano. Its
superiority is due to using 16 bit instruction, to
its larger ROM, to superior programming, and
especially to its vastly greater RAM, which permits
hash tables. Even the 16 MHz Fidelity Elite (version
2 or the new Premiere) and Fidelity Mach III only do
3.2 MaxMips, only marginally more than the Fidelity
Designer 2100 Display, but again the larger memory
and the 16 bit instructions make the difference. As
for the 68020, 3 cycles is the minimum, so the
Mephisto Vancouver 32 bit 12 MHz does 4 MaxMips and
the Fidelity Designer 2325 at 20 MHz does 6.67. For
the 68030 and 68040 the situation is rather
complicated, but the effective minimum seems to be
2.5 and 1.25 cydes respectively, 50 the Mephisto
Vancouver 68030 36 MHz does 14.4 MaxMips and the
Fidelity Version 10 (68040/25 MHz) does 20. Finally,
for RISC processors the minimum is normally 1 cycle
per instruction, so the "ChessMachine" at 15 Mhz
should be rated at 15 MaxMips, though in practice I
don't believe it is really as fast as the 68030 at
36 MHz, perhaps because RISC chips sometimes require
more than one instruction to do what a CISC (Le.
standard) chip can do in one. When comparing 8 bit
and 16 bit chips, it is very difficult to say how
much the ability to use 16 bit instructions is
worth, but I think you won't be too far off the mark
if you multiply the MaxMips of 16 and 32 bit chips
by 1.5 when comparing to 8 b Thus, the Elite
Premiere and the Travel Master processors are of
about equal power, with the 200+ point strength
difference being attributable primarily to the huge
difference in RAM and ROM, since each has the
world's best program for its hardware.
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