[OT?] MHz vs. MIPS in processors

[Chaos Master]

Hello people.

Reading some stuff about workstations, I find that the workstation speeds were
measured in MIPS (Million Instructions per Second).

Q: For someone new in the area, what is the biggest difference between telling
processor speeds in MIPS and in MHz?

[]s
--
© Chaos Master. | "I've tried so hard to tell
My Evanescence HP is at: | myself that you're gone
http://marreka.no-ip.com | And thought you were still
(most often offline... ) | with me..."
------------------------- -- Evanescence, "My Immortal"

 

[Norm Dresner]

Hello people.

Reading some stuff about workstations, I find that the workstation speeds were
measured in MIPS (Million Instructions per Second).

Q: For someone new in the area, what is the biggest difference between telling
processor speeds in MIPS and in MHz?

Megahertz (MHz) is just a measure of the frequency of the clocking signal
that goes to the CPU. Because of architectural differences, there's no
simple relationship that determines how many clock cycles it takes to
execute even a single instruction -- and in most CPU's the number of clock
cycles required to execute an instruction depends on xeveral things,
including the which instriction it is. Therefore MHz really doesn't work as
a way of comparing architecturally different CPUs. Therefore the concept of
measuring how many instructions per second a CPU could execute was developed
that that's the genesis of the Million Instructions per Second (MIPS)
measure. Even this isn't adequate and there are several "standardized"
benchmark programs that are sometimes used and the time it takes to run one
of these programs is a better way to compare different CPUs. Even then
there are ways to cheat and, ultimately, there is no absolutely perfect way
to compare the speeds of architecturally diverse CPUs.

Norm

 

[Dennis Clark]

: Hello people.

: Reading some stuff about workstations, I find that the workstation speeds were
: measured in MIPS (Million Instructions per Second).

: Q: For someone new in the area, what is the biggest difference between telling
: processor speeds in MIPS and in MHz?

The biggest difference is that MHz is a real quantifiable value of clock
speed, MIPS is a highly subjective marketing fluff word of little value.

DLC

: []s
: --
: ? Chaos Master. | "I've tried so hard to tell
: My Evanescence HP is at: | myself that you're gone
: http://marreka.no-ip.com | And thought you were still
: (most often offline... ) | with me..."
: ------------------------- -- Evanescence, "My Immortal"

 

[Daniel Watman]

: Hello people.

: Reading some stuff about workstations, I find that the workstation speeds were
: measured in MIPS (Million Instructions per Second).

: Q: For someone new in the area, what is the biggest difference between telling
: processor speeds in MIPS and in MHz?

The biggest difference is that MHz is a real quantifiable value of clock
speed, MIPS is a highly subjective marketing fluff word of little value.

DLC

So when you are choosing a microcontroller you choose the one with the
highest MHz do you? Doesnt matter that some types (eg PICs) divide the clock
by 4 internally while others run at the full speed (eg AVRs)?

MIPS will vary depending on the instructions you are executing, but it still
gives a much better idea of processing speed than MHz.

-Daniel

 

[John Miller]

Daniel Watman wrote to Dennis:

So when you are choosing a microcontroller you choose the one with the
highest MHz do you? Doesnt matter that some types (eg PICs) divide the
clock by 4 internally while others run at the full speed (eg AVRs)?

MIPS will vary depending on the instructions you are executing, but it
still gives a much better idea of processing speed than MHz.

Problem is, all MIPS aren't created equal. MIPS numbers between different
processor architectures/families may not be remotely comparable. That's
not to say that comparing clock speeds gives a better comparison; it
doesn't. For comparison, better to rely on a benchmark, e.g., 'stones or
flops.

 

[Chaos Master]

Norm Dresner ([email protected]) said those last words:

[snip. MHz vs. MIPS, the war]

Therefore MHz really doesn't work as
a way of comparing architecturally different CPUs. Therefore the concept of
measuring how many instructions per second a CPU could execute was developed
that that's the genesis of the Million Instructions per Second (MIPS)
measure. Even this isn't adequate and there are several "standardized"
benchmark programs that are sometimes used and the time it takes to run one
of these programs is a better way to compare different CPUs. Even then
there are ways to cheat and, ultimately, there is no absolutely perfect way
to compare the speeds of architecturally diverse CPUs.

I understand it now. Thanks.

[]s
--
© Chaos Master. | "I've tried so hard to tell
My Evanescence HP is at: | myself that you're gone
http://marreka.no-ip.com | And thought you were still
(most often offline... ) | with me..."
------------------------- -- Evanescence, "My Immortal"

 

[Chaos Master]

Dennis Clark ([email protected]) said those last words:

: Hello people.

: Reading some stuff about workstations, I find that the workstation speeds were
: measured in MIPS (Million Instructions per Second).

: Q: For someone new in the area, what is the biggest difference between telling
: processor speeds in MIPS and in MHz?

The biggest difference is that MHz is a real quantifiable value of clock
speed, MIPS is a highly subjective marketing fluff word of little value.

I always thought that MIPS = MHz or something like, so I sometimes said that a
1GHz Pentium III processor was 1000 MIPS. Now things make more sense

[]s
--
© Chaos Master. | "I've tried so hard to tell
My Evanescence HP is at: | myself that you're gone
http://marreka.no-ip.com | And thought you were still
(most often offline... ) | with me..."
------------------------- -- Evanescence, "My Immortal"

 

[Bob Myers]

I always thought that MIPS = MHz or something like, so I sometimes said that a
1GHz Pentium III processor was 1000 MIPS. Now things make more sense

Only if the processor in question executes, on average, one
instruction per clock cycle. That's not the norm, and in fact there
is no fixed number of clock cycles required per instruction that
applies to all processor architectures - so there's no equating
MIPS and MHz.

Having said that, though, the notion that "MHz is a real quantifiable
value of clock speed," as if that alone told you something about the
relative performance of various processors, is equally nonsensical.
You can compare performance by looking at clock speeds alone
ONLY if the processors in question have basically identical
architectures - but not in general. For instance, suppose we have
one processor which on average requires four clock cycles to
complete an instruction, while another requires only two. Further
assuming that the instruction sets of the two are comparable (in
simple terms, you "get as much done" per instruction, on average,
between the two), then the second processor at 2 GHz will outperform
the first at 3 GHz. So...it ain't that simple. And you definitely don't
have anything to brag about if you look at clock rates alone.

This whole situation is what leads to performance benchmark
testing, in which programs are written to simulate the sort of real-
world tasks that the processor will be called upon to do. You
run these benchmarks on the processors you want to compare,
and the one which finishes the job first is the higher-performance
processor. Simple, and not as subject to marketing spin as the
more-simplistic MIPS or MHz numbers alone.

Bob M.

 

[Ian Bell]

: Hello people.

: Reading some stuff about workstations, I find that the workstation
: speeds were measured in MIPS (Million Instructions per Second).

: Q: For someone new in the area, what is the biggest difference between
: telling processor speeds in MIPS and in MHz?

The biggest difference is that MHz is a real quantifiable value of clock
speed, MIPS is a highly subjective marketing fluff word of little value.

Personally I would have said it was the other way round. I know many chips
that used a higher frequency oscillator and internally divided it. Quoting
the oscillator frequency of these is quite misleading. MIPS on the other
hand is clearly quantifiable no matter what the clock speed. OTOH 10 MIPS
of crap instructions may be no better than 5MIPS of a highly optimised
instruction set.

Ian