Two-core technology
Single-core processors that run multi-threaded applications become less cost effective with each
increase in frequency. This is because the multiple threads compete for available compute resources,
which limits the increase in performance at higher frequencies. Increasing the CPU core frequency not
only delivers lower incremental performance gains, but also increases power requirements and heat
generation. These factors create significant barriers for single-core architectures to keep pace with the
growing needs of data centers.
To address the performance, power, and cooling complexities, Intel announced its first two-core
processor architecture in 2005. A two-core processor is a single physical package that contains two,
full processor cores per socket. The two cores have their own functional execution units and cache
hierarchy (L1 and L2); however, the OS recognizes each execution core as an independent
processor.
Figure 6 illustrates the difference between single-core and two-core processors with HT Technology. In
the case of the single-core processor, HT Technology allows the OS to schedule two threads on the
core by treating it as two separate "logical" processors with a shared 2-MB L2 cache. The two-core
processor builds on HT Technology with two execution cores. Each core has its own 2-MB L2 cache
and separate interface to an 800-MHz front side bus. The two-core architecture runs two threads on
each execution core, allowing the processor to run up to four threads simultaneously. The second
core's additional capacity reduces competition for processor resources and increases processor
utilization. Thus, the performance improvement of a two-core processor is in addition to the
improvement due to HT Technology.
A two-core processor has better performance-per-watt than a single-core processor running at a higher
frequency. This is analogous to the way a wide pipe, by virtue of its volume, can carry more water
than a smaller pipe with a higher flow rate. Likewise, the two-core architecture is designed to make
processors perform more efficiently at lower frequencies (and lower power consumption levels). The
two-core processor allows a better balance between performance and power requirements. It was the
first step in multi-core processor technology.
Figure 6. Implementation of Hyper-Threading Technology on single processor core (left) and two-core processor
(right)
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