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Extended hyper-pipeline

In keeping with its history of regularly increasing processor frequencies, Intel extended the hyper-

pipeline queue from 20 (in the earlier Pentium 4 design) to 31 stages. The biggest drawback to this

approach is that, as the pipe gets longer, interruptions (stalls) to the regular flow of instructions in the

pipe become progressively more costly in terms of performance. To mitigate such stalls, Intel improved

the branch-prediction algorithm sufficiently to prevent this deeper pipeline from causing performance

degradation.

SSE3 instructions

The Prescott design added Streaming Single-Instruction-Multiple-Data (SIMD) Extensions 3, or Prescott

New Instructions. As they did in earlier processors, SIMD instructions provide the potential for

improved performance because each instruction permits operation on multiple data items at the same

time. Prescott processors had newer versions of arithmetic, graphics, and HT synchronization

instructions.

The arithmetic group consists of one new instruction for converting x87 data into integer format, and

five instructions that simplify the process of performing complex arithmetic. Complex numbers actually

consist of two numbers: a real and an imaginary component. The additional instructions facilitate

complex operations because they are designed to operate on both parts of these complex pairs of

numbers at the same time. Using these instructions also simplifies coding complex arithmetic

operations because fewer instructions are needed to accomplish the goal.

The graphics group contains one instruction for video encoding and four that are specific to graphics

operations. Finally, two instructions facilitate HT operation, for example, by allowing one operational

thread to be moved to a higher priority than another.

64-bit extensions —Intel 64

In response to market demands, Intel added 64-bit extensions to the x86 architecture of the Xeon,

Xeon MP, and Pentium 4 processors. The key advantage of 64-bit processing is that the system can

address a much larger flat memory space (up to 16 exabytes). Even though the 32-bit architecture

can actually access up to 64 GB of memory, access above the standard 4 GB limit must go through a

slow and cumbersome windowing facility such as Physical Address Extension (PAE). Due to the

complexities of this process, most 32-bit applications have not made use of the higher address space.

Today, few applications require more than 1 or 2 GB of memory; however, this will eventually

change. By adding 64-bit extensions to its x86 processors, Intel has provided users with the same 64-

bit addressing benefit at a much lower cost than if users were forced to replace both the hardware

and software.

Even though the larger memory addressing capability is the primary advantage of 64-bit extensions, it

is not the only one. The 64-bit extensions also provide a larger register set with eight additional

general purpose registers (GPR) and 64-bit versions of the existing registers. With a total of 16 GPRs,

64-bit extensions provide additional resources that compilers can use to increase performance.

64-bit Extensions

AMD was first to release 64-bit extensions―called AMD64―with its Opteron

processor in early 2003. Within a year, Intel responded with its own plans to

deliver a similar solution called Extended Memory 64 Technology, or EM64T,

which is broadly compatible with AMD64. In late 2006, Intel began using the

name Intel 64 for its implementation. Intel 64 and AMD64 use the same register

sets and definitions, and the 64-bit instructions are nearly identical. HP expects

that any minor differences will be handled by the OS and compiler, so that the

average application writer or customer should see no differences. New operating

systems are required to make use of 64-bit extensions. Red Hat, SUSE, and

Microsoft provide AMD64 support and Intel 64 support.