Advanced Dynamic Execution
Intel describes the Advanced Dynamic Execution being an out of order speculative
execution engine. This Engine keeps the execution units executing instructions.
This is accomplished by providing a large window of instructions from which
the execution units can choose. The large out of order instruction window
allows the processor to avoid stalls that might occur while instructions are
waiting for dependencies to resolve. Intel’s previous P6 architecture featured
a small window with 42 instructions, compared to the NetBurst architecture
that can have up to 126 instructions in this window (in flight).
This technology at the same time features an improved branch prediction capability.
The Pentium 4 is estimated to reduce branch miss-predictions by around 33%
compared to the P6 architecture’s branch prediction capability. This is achieved
by implanting a 4K branch target buffer that is used to store more detail
on the history of past branches and as well as by implementing a more advanced
branch prediction algorithm.
Rapid Execution Engine
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The
new architecture permitted the Pentium 4 to run the Arithmetic Logic Units
(ALUs) two times the frequency of the Processor’s core it self. This means
that the Arithmetic Logic Units on a Pentium 4 running at 1.5 are operating
at 3GHz with a latency that is half the duration of the core clock. This can
be directly translated in higher through and reduced latency of execution.
400MHz
Front Side Bus
One of the most talked features of the Pentium 4 is its 400MHz BUS. The Pentium
III Processor’s 133MHz bus, which is 64-bit Wide, is capable of delivering
1.06GB/S of data. The Architecture of the Pentium 4 is somewhat different.
The Pentium 4’s bus is clocked at only 100MHz at also 64-bit Wide, what differs
here is that the 100MHz is quad pumped and is capable of achieving a whooping
3.2GB/s peak.
Advanced Transfer Cache
Intel’s Pentium III features 8KB of L1 data
cache. This is half the size of what the Pentium III features. This may seem
a bit confusing at first, but smaller caches have lower latencies. This was
done in order to decrease the latency of the L1 memory, this should result
in an improved transfer rate but at the same time, the little size (8K) might
not be enough for some specific tasks.
This is where the L2 memory comes in mind. The Pentium 4, like the Pentium
III (Coppermine), spots 256k of on-die-cache on a 256-bit bus. However, there
is a difference between both. The new architecture of the Pentium 4 permits
to transfer data on each clock, compared to the Pentium III (Coppermine) that
is transferring data on every other Cycle.
Execution Trace Cache
This technology caches decoded x86 instructions (micro-ops), thus removing
the latency associated with the instruction decoder from the execution loop.
The Execution Trace Cache stores the micro-ops in the path of program execution
flow, where the results of branches in the code are integrated into the same
cache line.
Execution Trace Cache is another handy technique Intel implemented in its
new Architecture to ease the penalty of miss-Predicted Branch instructions.
On older Intel processors, based on previous architectures, if the branch
instruction was miss-predicted, the processor needed to start the process
from the beginning. The NetBurst architectures permits to go directly through
the Execution Trace Cache Technology to retrieve the micro-op and then send
it through execution pipeline without having to restart the process from the
first phase.
Streaming SIMD Extensions 2 (SSE2)
Intel’s Pentium 4 architecture features 144 new instructions capable
of delivering 128-bit SIMD integer arithmetic operation and 128-Bit SIMD Double
Precision Floating Point. In order to take benefit of these new features,
current software-games will need to be re-compiled; otherwise, there will
be no benefit. As with SSE, Game/Software developers should be incorporating
SSE2 features in their code with no delays. These instructions can reduce
the overall number of instructions required to execute a specific task and
at the same time can result in a performance increase.
