Dual processors- Why?

[PaulCsouls]

Is there a general performance enhancement with dual processor boards
or is there only an advantage with certain applications?

Paul

 

[John R Weiss]

Is there a general performance enhancement with dual processor boards
or is there only an advantage with certain applications?

There is a general enhancement.

Win 2000 and XP Pro can allocate OS tasks among the processors as well as
individual processes within applications. Also, CPU-intensive background
apps will work without interfering with foreground tasks running on the
other CPU. There will be even further enhancement with SMP-aware apps such
as Photoshop (v5.5 and later).

As a datapoint, my dual P-III/550 ran the Business Winstone twice as fast as
my single P-III/1200 laptop.

 

[JK]

A better question to ask would be whether a dual processor system
will outperform a single processor system of the same cost. That would
probably mean using a faster processor than those used in the dual
system, a 10,000 rpm hard drive in the single cpu system vs a 7,200
rpm one in the dual processor system, and perhaps a better video card
and more ram in the single processor system. A motherboard for dual
processors is also more expensive than for a single one. If one wants
to use Windows, XP professional needs to be used with dual processors,
while XP home can be used with a single processor.

 

[PaulCsouls]

Okay, I'll add some specifics.

Two Intel Xeon 2.4GHz 533MHz FSB 512 Cache for $222.00 each and a $250
Motherboard

VS

One Athlon 64 3700+ 2.4GHz 1MB Cache for $519.00 and a $75.00 Mother
board

Does 64 bits beat 2 processors?

 

[John R Weiss]

A better question to ask would be whether a dual processor system
will outperform a single processor system of the same cost.

Not necessarily...

Though you are not likely to be able to find a dual system at the same cost
as a low-end single-CPU system (except in a used machine, which I just
happen to have available...), it is likely that a person looking for
performance is willing to pay for that performance.

Whether a high-end single-CPU machine will outperform a low-end dual-CPU
machine depends on both the respective hardware as well as the use to which
the machine is put. In general, the high-end single will likely outperform
the dual in a single-app environment, while the dual will work better in a
multitasking environment. Of course, you can always "choke" any machine by
underspecifying a single component, such as RAM or HD...

 

[John R Weiss]

Okay, I'll add some specifics.

Two Intel Xeon 2.4GHz 533MHz FSB 512 Cache for $222.00 each and a $250
Motherboard

VS

One Athlon 64 3700+ 2.4GHz 1MB Cache for $519.00 and a $75.00 Mother
board

Does 64 bits beat 2 processors?

Not yet...

However, you can have both with a dual Opteron system...

 

[John McGaw]

A better question to ask would be whether a dual processor system
will outperform a single processor system of the same cost. That would
probably mean using a faster processor than those used in the dual
system, a 10,000 rpm hard drive in the single cpu system vs a 7,200
rpm one in the dual processor system, and perhaps a better video card
and more ram in the single processor system. A motherboard for dual
processors is also more expensive than for a single one. If one wants
to use Windows, XP professional needs to be used with dual processors,
while XP home can be used with a single processor.

The dual vs. single question has been tested pretty thoroughly over at Tom's
Hardware and they seem to think that the dual Xeon has some advantages over
the fastest P4. I suspect that, like most benchmarking tests, a lot depends
on which tests you care to run.

http://www.tomshardware.com/motherboard/20040514/index.html

 

[PaulCsouls]

The dual vs. single question has been tested pretty thoroughly over at Tom's
Hardware and they seem to think that the dual Xeon has some advantages over
the fastest P4. I suspect that, like most benchmarking tests, a lot depends
on which tests you care to run.

http://www.tomshardware.com/motherboard/20040514/index.html

Cool link. That pretty much answers my question. Dual processors seem
to offer little for game playing like Quake and alot for video
applications. I wonder if DOOM 3 uses hyperthreading.

Paul

 

[JK]

That is not a fair comparison, as the hard drive on a notebook is typically
much slower than the hard drive on a desktop. The graphics subsystem on
a desktop is also typically much faster than that of a notebook.

 

[John R Weiss]

As I said, it's a data point...

FWIW, the desktop has a 32 MB (dedicated) graphics system, and the laptop
has a 64 MB (shared RAM) system.

Another benchmark (SI Sandra), which separates all the subsystems, confirms
that in EVERY case the dual-CPU desktop is faster. The 2 (arithmetic and
multi-media) CPU benchmarks were each 1.35 times faster on the dual 550,
compared with the single 1.2 GHz; memory bandwidth was 3.7 x; and the file
system (HD) was 2.4 x.

So, even though the 2 CPUs were not able to process data much faster once
the data got to them, they were served up that data much faster from RAM...

 

[David Maynard]

As I said, it's a data point...

The question is whether it's a meaningful data point.

FWIW, the desktop has a 32 MB (dedicated) graphics system, and the laptop
has a 64 MB (shared RAM) system.

^^^^^^^^^^^^ BIG difference

Another benchmark (SI Sandra), which separates all the subsystems, confirms
that in EVERY case the dual-CPU desktop is faster. The 2 (arithmetic and
multi-media) CPU benchmarks were each 1.35 times faster on the dual 550,
compared with the single 1.2 GHz; memory bandwidth was 3.7 x; and the file
system (HD) was 2.4 x.

So, even though the 2 CPUs were not able to process data much faster once
the data got to them, they were served up that data much faster from RAM...

They were served faster from RAM because the video memory, shared out of
RAM, in that notebook is sucking up memory bandwidth at the display refresh
rate.

An optimistic rule of thumb is that you get about 80% of the combined speed
on a dual system so dual 550s would be roughly equivalent to an 880 of the
same processor type, all else being equal.

A more conservative estimate is getting about 50% of the 'second'
processor, which would place dual 550s around 825.

Regardless of which calculation one thinks is the best estimate it's rather
intuitive that two 550s, even summing to 1100, can't possibly be 'twice as
fast' as one 1200 of the same processor class unless something other than
the processors is at play.

 

[JK]

I expect the Athlon 64 3700+ to be much faster in most applications.
The Xeon is essentially a Pentium 4 that can be used in a dual
configuration. You might want to consider an Athlon 64 3800+
if you plan to do gaming or other high bandwith software, as it
has dual on chip memory controllers. Also keep in mind that
with a single Athlon 64 you can use Windows XP home, while a dual
Xeon system Would require Windows XP professional, so the
Athlon 64 3800+ would be more compare in price than the Athlon 64 3700+.
Even with 32 bit software, I would expect the Athlon 64 to come out
ahead with the vast majority of software. With 64 bit software, the
Athlon 64 performance would really be superb. Even with a 64 bit OS
and 32 bit software the Athlon 64 might perform much better in
many applications than its already great performance running 32
bit software with a 32 bit OS.

 

[King Lear]

It really depends on what you do with your PC. If you multitask a lot,
especially running a CPU-intensive background job while working with an
interactive application, then go with a dually. You'll get much better
overall system response.

If you run mostly background/batch jobs or a single CPU-intensive task
such as gaming then a comparable single-CPU system will perform better
and cost less.

Another plus about a dually system is that it has a built-in damage
control: a run-away process (assuming it is only single-threaded) in
general won't kill your system.

/kl

 

[PaulCsouls]

Thanks for the info. According to Tom's Hardware evaluation dual
processors are not much better at gaming applications.
I'm looking into a DOOM3 machine since I don't think my AMD K6-2
450MHz will cut it. It's still running with case, power supply and
monitor I bought with my 486, so I'm going to need the works. Anyway
Dual processors sound like a neat thing to have but I don't think it's
right for me. I'll definitely look at the Athlon 64s.

Check out the DOOM3 benchmarks.

http://www2.hardocp.com/article.html?art=NjQy

Paul

 

[JK]

That Hardcop article is a review of video cards, not processors.
Take a look at this review.

http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=2065&p=1

 

[John R Weiss]

Regardless of which calculation one thinks is the best estimate it's rather
intuitive that two 550s, even summing to 1100, can't possibly be 'twice as
fast' as one 1200 of the same processor class unless something other than
the processors is at play.

That could well be true for a system running a single app. However, once
you get into multitasking, a dual-CPU system will be much more effective. I
run database queries on my systems that hog an entire CPU for 15-60 seconds
at a stretch. On the single-CPU machine, all other processes stop cold. On
the dual, I work merrily along while the DB ferments in the background.

Also, it is difficult to compare 2 systems -- 1 single-CPU and 1 dual-CPU --
that are otherwise totally equal. Maybe I'll dust off my old 550, pull out
a CPU, and compare scores...

 

[John R Weiss]

I expect the Athlon 64 3700+ to be much faster in most applications.
The Xeon is essentially a Pentium 4 that can be used in a dual
configuration. You might want to consider an Athlon 64 3800+
if you plan to do gaming or other high bandwith software, as it
has dual on chip memory controllers.

Another option is a dual Opteron setup. The Opteron 2xx series is the
dual-capable version of the socket 939 Athlon 64.

The Athlon 64 3500+ (2.2 GHz) costs about $350 at newegg, and the 3800+ (2.4
GHz) is $640.

The Opteron 240 (1.4 GHz) can be had for about $190 each, the 244 (1.8 GHz,
at the "knee in the price curve right now) for $325 each, and the latest 250
(2.4 GHz) goes for $825.

For the gamer, the 3500+ may be the reasonable-cost answer. I like my dual
246s...

 

[PaulCsouls]

Looks like I should get a 939 socket chip that fits into my budget and
that will leave me a reasonable upgrade path for a few years.

 

[DaveW]

ONLY with applications written to take advantage of dual processors, which
are very few in number. Also the OS must be written to use dual CPU's.
Windows XP Home, for instance, is not.

 

[David Maynard]

That could well be true for a system running a single app.

It's inherently true: 1100 can't possibly be bigger than 1200, much less
'twice' as big.

However, once
you get into multitasking, a dual-CPU system will be much more effective.

The comment was about 'speed', which I presumed meant processing power.
'Effective' is another matter, depending on what you mean by it.

I
run database queries on my systems that hog an entire CPU for 15-60 seconds
at a stretch. On the single-CPU machine, all other processes stop cold.

Well, they shouldn't 'stop cold' unless you've got priorities set to
allocate CPU time exclusively to the database app.

On
the dual, I work merrily along while the DB ferments in the background.

That is easily explained by postulating that the database app runs on only
one processor so there's half of the system left 'idle' for your other apps
to run in. That would be true regardless of what the combined 'speed' is
and doesn't say anything about it.

Also, it is difficult to compare 2 systems -- 1 single-CPU and 1 dual-CPU --
that are otherwise totally equal. Maybe I'll dust off my old 550, pull out
a CPU, and compare scores...

I don't understand why you say the comparison of otherwise equal systems is
'difficult'.