Hardware Reference
In-Depth Information
to the speed of the motherboard, whereas the back-side or L2 cache bus is coupled to the speed of the
processor core. As the frequency of processors increases, so does the speed of the L2 cache.
DIB also enables the system bus to perform multiple simultaneous transactions (instead of singular
sequential transactions), accelerating the flow of information within the system and boosting
performance. Overall, DIB architecture offers up to three times the bandwidth performance over a
single-bus architecture processor.
HT Technology
Intel's HT Technology allows a single processor or processor core to handle two independent sets of
instructions at the same time. In essence, HT Technology converts a single physical processor core
into two virtual processors.
HT Technology was introduced on Xeon workstation-class processors with a 533MHz system bus in
March 2002. It found its way into standard desktop PC processors starting with the Pentium 4
3.06GHz processor in November 2002. HT Technology predates multicore processors, so processors
that have multiple physical cores, such as the Core 2 and Core i Series, may or may not support this
technology depending on the specific processor version. A quad-core processor that supports HT
Technology (like the Core i Series) would appear as an 8-core processor to the OS; Intel's Core i7-
3970x has six cores and supports up to 12 threads. Internally, an HT-enabled processor has two sets
of general-purpose registers, control registers, and other architecture components for each core, but
both logical processors share the same cache, execution units, and buses. During operations, each
logical processor handles a single thread (see
Figure 3.4
).
Figure 3.4. A processor with HT Technology enabled can fill otherwise-idle time with a second
process for each core, improving multitasking and performance of multithreading single
applications.
Although the sharing of some processor components means that the overall speed of an HT-enabled
system isn't as high as a processor with as many physical cores would be, speed increases of 25% or
more are possible when multiple applications or multithreaded applications are being run.
