IA-64

What is IA-64 (Intel Architecture 64)?

IA-64 or Intel Architecture 64 refers to the 64-bit processor architecture. It is developed by Intel and Hewlett-Packard and features the Itanium series of processors that are specifically designed to be used in server processing.

Technically, this specific architecture is built on explicit parallelism at the instruction level where it is the compiler that decides which particular instructions are to be carried out in parallel, as opposed to the superscalar architecture.

Understanding IA-64 (Intel Architecture 64)

Understanding IA-64 (Intel Architecture 64)

IA-64 is often referred to as Intel Itanium architecture because this specific ISA or Instruction Set Architecture features in the Itanium family of 64-bit Intel CPUs.

However, the fundamental specs of the ISA were initiated at HP but were then employed by Intel in collaboration with them.

It was in 2001 when the first Itanium processor was released by Intel under the codename Merced.

This particular architecture relies on explicit instruction-level parallelism. The instructions that are to be executed in parallel are typically determined by the compiler.

This is actually to the contrary of the superscalar architectures that typically relies on the processor to deal with the instruction dependencies during runtime.

Some of the useful features included in the design of the IA-64 architecture are:

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Another useful and unique feature of the IA-64 is that it employs ‘predication’ which allows it to predict the future. This helps it and the processor to take the full advantage of the superior pipeline architecture.

With such useful features of the IA-64 architecture, the cores of all Itanium processors, including Tukwila can perform up to six instructions in one clock cycle.

The key to such potential in this specific architecture is the capability to run processor optimized codes.

Moreover, since the compiler plays a significant role, its technology is far more improved so that it matches easily with the specs of this architecture.

It is due to this improved compiler that codes are explicitly parallelized and allows much improved utilization of the CPU.

A branch instruction following a compare is carried out in parallel from both sides.

When a particular branch is determined to be correct, the result of the other branch is gotten rid of because it is of no use anymore.

The compilers of the IA-64 set up this prediction by interleaving the instructions and adding codes.

This tells the processor how exactly it should execute it in parallel.

However, when there is no such prediction set up, the processor performs an easier prediction.

Here, it does not execute both sides of the branch but only that side of it in parallel, which it assumes to be the outcome.

It may not always be right with its prediction, and when the guessing is wrong, the parallelism is lost along with a few nanoseconds.

The compiler for the IA-64 uses inter-procedural compilation. There are significant benefits to it that ensure a much higher performance level.

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Apart from that, the compiler also tries to initiate loads earlier than the schedule. This allows the data to take more time to arrive and therefore it does not need stalling the processor.

The IA-64 architecture also allows running the legacy code successfully and for that you do not need to make any modifications.

However, the performance may not be very good.

Moreover, though applications and programs written for x86 computers run quite well on the IA-64 computers through translation layers, some recompilation is, however, needed.

This will help in taking the full advantage of IA-64.

IA-64 Vs x64

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What is Windows IA-64?

Windows IA-64 refers to the Intel Itanium 64-bit processors that come with more advanced compiler capabilities.

It is the 64-bit Intel architecture that does not support running those 32 bit applications as in the x64 processors.

You will typically need a special edition of Windows to run them on these CPUs.

Is IA-64 RISC or CISC?

Ideally, the IA-64 is a lot different from both the Reduced Instruction Set Computer or RISC and the Complex Instruction Set Computer or CISC because it uses Very Long Instruction Word or VLIW architecture.

However, the fact that it attempts to shift complication from the hardware to its compiler, makes it more of a RISC than a CISC.

Conclusion

IA-64 is the particular ISA of Intel that features in their Itanium 64-bit CPUs. It supports explicit parallelism at the instruction level.

The compiler in this specific architecture plays a significant role in handling and resolving the dependencies between instructions by deciding which of those should be executed in parallel.