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Multi-core Processors By Brian K. Lewis, Ph.D.,
member of the Sarasota PCUG, Florida
February
2006 issue of the
Sarasota PC Monitor www.spcug.org
When I first started researching central
processing units (CPUs) my idea
was to try to make some sense out of the naming/numbering schemes
currently
being used by Intel and AMD. This turned out to be an almost impossible
task.
Did you realize that Intel has more than 50 different Pentium 4 CPU
models?
That in each speed range there can be a dozen different models. They
vary by
cache size, socket size, hyper-threading or not, 64 bit or not, voltage
and
other parameters. As just one example, Intel's 3.2 GHz processor has 12
different models. AMD is just about as bad when you try to analyze
their
nomenclature. So, for the moment, I have given up on trying to find a
simple
way to categorize the currently available CPUs. Maybe next month.
Since the upper end of the CPU production
now seems to be aimed at
producing processors with more than one central core, I decided to look
at that
topic. So what does it mean that a CPU has more than one core? You can
think of
it as a single chip containing two or more central processors. It is
like
having two (or more) computers in one box. That said, I have to admit
that it
doesn't double your processing speed. At least, not yet.
Servers and workstations used in business
have had multiple processors
for a number of years. Mainframe computers with multiple processors
have also
been around for years. In order to take advantage of multiple
processing your
operating system must be capable of recognizing and using multiple
processors.
Windows has had that capability since Windows NT/2000 and it is
included in
Windows XP. Intel introduced Hyper-threading technology in 2002. That
allowed
two different “threads” to be processed almost simultaneously. Going
the next
step and putting multiple processors on one single chip is the idea
behind
multi-core processors. The AMD64 chip
was originally designed to have a second core added at a later date.
This
became the current Athlon 64 X2 dual-core processor. Intel's Pentium D
is also
a dual-core processor. In any multi-core
processor each core is seen by the operating system as being a discrete
processor as if the motherboard had two or more separate CPUs. Ideally
this
allows the computer to process more work within a given clock cycle.
The question is why would Intel and AMD
want to complicate CPU design by
putting these processors onto a single chip? The design is more
expensive to
produce. The primary answer to the questions is heat. In the fall of
2002 Intel
indicated that it had a 4.0 GHz processor in production. That processor
never
reached the market. There was also talk about processors reaching 10
GHz. That
has all changed and primarily due to the difficulty of reducing the
heat output
of these processors. When you have 125 million transistors in a very
small
space, as in Intel's Prescott processor series, there is a lot of heat
produced. In fact, it takes special cooling to keep the processor from
overheating and essentially burning itself up. I have a 3.0 GHz Intel
“Prescott” processor in my computer and it runs at a consistent 400
Celsius (1040 F). That's only because I have an over sized
copper
heat sink and very large CPU fan. Ideally it should be running in the
low 30's
which would be about 50% of the maximum temperature.
Another problem is current or electron
leakage. As the processor die
size decreases and the number of transistors increases, there is a
greater
problem with leakage. Electron leakage from one pathway to another can
result
in data corruption. Die sizes are currently 90 nm and are anticipated
to drop
to 65 nm this year. Finally the power requirements increase with the
increase
in transistors. The increase in power is another component in the
increasing
amount of heat produced by the CPU.
Dual core processors are designed to run
at lower clock speeds than the
fastest of the single core processors. This reduces the heat output
even though
the dual core processors currently have 230 million transistors in a
smaller
space. Intel has also announced another dual core processor to be on
the market
this summer that will have 1.7 billion transistors! Their literature
says they
anticipate that by the end of 2006, 70% of their desktop and mobile
processors
will be dual-core. By the end of 2007 fully 90% of Intel's processors
will be
at least dual-core. AMD is moving just as fast in producing dual core
processors. As the number of cores increase on a single die there will
definitely be increases in heat output. Cooling requirements for these
CPUs
will definitely increase. The future of CPU cooling would seem to be
water-cooled systems even for the home desktop market. Unless there is
some
technological break-through that will reduce the heat problem.
There are other bottlenecks that will
become more important in
multi-core systems. One is the bus that transmits information from the
core to
other components. With two or more cores sending information over the
bus, both
speed and bandwidth will have to increase to handle the increased load.
The CPU
depends on the computer RAM for the source of its data and
instructions.
Therefore memory speed is also important and will need to be increased.
Finally, information is read from and written to the hard disk. Even
with the
increased speed and bandwidth associated with SATA drives, this can be
the
largest bottleneck in the system. So these problems can prevent the
user from
gaining the maximum advantage provided by a multi-core system. All that
said, I
have to admit that there will be some definite gains in processing
speed with
the multi-core systems. This has already been demonstrated by a number
of
third-party testers. However, it will be some time before a dual-core
system
will function at twice the speed of a single core system.
I keep talking about “threads” without
really giving you any explanation
of them. I don't think you really want to go into the programming
background
for this, so I will try to give you the simple explanation. A thread is
a
series of sequential programming steps or operations. In some
instances,
programming steps can be executed simultaneously. However, the program
must be
designed to allow this to happen. There are also problems associated
with
multi-threading that can slow down the overall operation. One problem
is called
“deadlock”. This is when two threads are each waiting for the other to
complete
its operations. This can result in neither thread reaching completion.
For
software developers, multi-threaded applications have much higher
development
costs than the current single-threaded applications. Although Intel's
Hyper-threading CPU's have been around for several years, very little
software
has been written to take advantage of the dual-thread processing. Both
Intel
and AMD are working with software developers to produce more
multi-threaded
software applications. But it may be some time before the majority of
software
applications can take advantage of multi-core processors.
Intel has another technology it has
developed for use in its multi-core
chips. This is called “Foxton”. This allows a processor to adjust its
speed and
power requirements based on its processing load. Each process will have
a base
or minimum clock speed and a maximum speed. When the load is low, the
processor
can raise its clock speed up to a maximum level. This gives the
processor more power
for faster computing. If the load or the power requirement rises too
high, the
processor slows. All of this is more technology to simply reduce the
system
heat to manageable levels.
As I was writing this, Steve Jobs, at MAC
World in San Francisco, announced
the introduction of Intel based Macintosh computers using the Intel
Core Duo
processor. This processor was developed for the mobile computer market.
It uses
clock speeds from 1.6 GHz to 2.1 GHz. Although it has a lower clock
speed, the
dual processor will provide some performance gain. There will also be a
lower
drain on the battery. Several other companies have produced Windows
based
laptops using this same processor.
So how will multi-core computers affect
the individual computer user? It
should improve the efficiency of your computer by improving its
multi-tasking
ability. Since each core is essentially a separate processor, at least
two
applications can be run simultaneously. If the dual core also supports
hyper-threading, as some of the Intel Pentium D CPUs do, then it could
handle
four applications or four threads in multi-threaded applications. Now
you may
think you really don't do any multi-tasking. However, it you are
running an
anti-virus program, a firewall, or any other application in the
background
while you also do word processing or emailing, then you are
multi-tasking. A
dual core CPU would permit this to happen more efficiently, if not more
quickly. Frequently, I am writing, checking a spreadsheet and pulling
data off
the web. This is also multi-tasking.
I suspect
that if you plan
to replace your computer within the next year (or two), you will have a
dual-core 64-bit processor in your system. With a couple of Gigabytes
of RAM,
you'll be all set to run Windows Vista as a 64-bit operating system.
Dr. Lewis
is a former
university & medical school professor. He has been working with
personal
computers for more than thirty years. He can be reached via e-mail at
bwsail(at)yahoo.com.
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