Rapid advances in processor technology, illustrated by the leap from single-core
to dual-core and then to multicore processors, have made the task of picking
a processor for your system more difficult than ever. In addition, there are
different processor architectures to choose from. Understanding the differences
in these technologies can help you select the right system and processor combination
for your business.
The processor war between Intel and
AMD is the force driving this rapid advance
in technology. In the mid-to-late 1990s, it
seemed that Intel had the processor race all
locked up—until the company tried to push
the market toward its new 64-bit Itanium
processor in 2001. Intel stumbled, however,
by making the Itanium binary-incompatible
with x86 software, which opened the door
for AMD's 2003 release of the AMD Opteron,
a 64-bit, x86-compatible x64 processor. The
Opteron supplanted the Itanium in the general-purpose server market and enabled AMD
to gain significant server market share at
Intel's expense.
Following the success of the Opteron and its Direct Connect Architecture, Intel
revamped its system architecture, moving from its NetBurst microarchitecture
to the higher-performing, more power-efficient Intel Core microarchitecture,
and launched its own x64-compatible processors. Since then, the Itanium has
been relegated to serving only very high-end, processor-intensive workloads,
while x64 architecture has become the current server standard. On the surface,
AMD's and Intel's multicore, x64-compatible processors might seem the same,
but there are significant differences in how they operate that you should be
aware of before you choose between them.
Ante Up with Dual-Core
On the heels of their move to x64 architecture, both AMD and Intel jumped into
dual-core processing technologies. The ability to improve processing power simply
by boosting processor speed had reached a plateau, and both chip manufacturers
realized that the easiest path to more power was through parallelism. The ever-shrinking
size of processors made it possible to produce dual-core chips, which combine
two processors on one die. This approach had the added benefit of nearly doubling
the available CPU power while using the same power envelope (i.e., the same
wattage requirements) as a single processor.
In 2005, Intel became the first to enter
the dual-core market with the release of the
Pentium D processor, built using the Intel
NetBurst microarchitecture. In January 2006,
Intel switched to the Core microarchitecture.
Based on Intel's Pentium M mobile processors, the Core microarchitecture uses a shorter
instruction pipeline than does NetBurst, letting
processors execute substantially more instructions per clock cycle and achieve higher levels
of performance even though they run at a
lower clock frequency than earlier Intel CPUs.
AMD quickly countered Intel's move with its
own 64-bit dual-core Athlon 64 X2.
The two manufacturers' dual-core designs
use quite different architectures. Intel uses a
shared front-side bus technology that gives
each processor half the bandwidth of the frontside bus. Memory and I/O access operations
also share the bus, making the bus speed a
critical factor in overall system performance.
Intel's latest dual-core processor, the Core 2 Duo, is built using 65 nanometer
(nm) technology. The Core 2 Duo and Core 2 Extreme CPUs integrate both cores
on a single die. Each core has 64KB of dedicated L1 cache that consists of a
32KB instruction cache and 32KB data cache, and both cores share a 4MB L2 cache.
The Core 2 Duo features one-cycle throughput for 128-bit floating-point Streaming
Single-Instruction, Multiple-Data Extensions (SSE) instructions, which are used
for complex math and graphical-display processing. It also has a new power-saving
design and a front-side bus that runs at 1066MHz.
AMD uses a completely different design for
its dual-core processors. In AMD's Direct Connect Architecture, each CPU has an integrated
memory controller. The HyperTransport bus
allows an 8GBps direct connection between
the CPUs, I/O, and memory. In February 2007,
AMD released new dual-core Opterons that
offer higher clock speeds—up to 2.8GHz—and
greater power efficiency than earlier models;
the company will push its dual-core designs to
3GHz later this year.
Dual-core processors are both successful
and popular. Today, most servers and many
business desktops benefit from the speed and
power efficiency of dual-core processors.
Double Down with Quad-Core
Following the same path that led to dual-core processors, Intel and AMD have
doubled the stakes and jumped from dual-core to quadcore chip designs. With
the release of the Quad-Core Intel Xeon processor 5300 series in November 2006,
Intel is clearly ahead in the game. AMD won't have an entry until mid 2007,
when it will enter the market with a quad-core chip code-named Barcelona. Just
as with the dual-core processors, Intel and AMD offer significantly different
quad-core designs.
The Intel quad-core design combines two dual-core processors onto a single
chip. In other words, instead of being a "native" quad-core processor, Intel's
quad-core Xeon is actually a dual dual-core chip. Although this architecture
enabled Intel to get its quad-core chip to market early, the design isn't optimal.
When processors that are on separate cores exchange data, the data must be sent
over the front-side bus and through the memory controller, which isn't the most
efficient mechanism. In addition, as with previous Intel designs, this approach
makes the overall system speed dependent on the speed of the front-side bus.
Despite these drawbacks, improvements in the Intel Core microarchitecture and
the additional CPUs cumulate to make Intel's quad-core chips the fastest x64compatible
processors available today. Figure 1
shows Intel's quad-core design. You can find more details about Intel's quad-core
processors at http://www.intel.com/quad-core/index.htm?qc_tl+techresearch_promo&.
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