IA-64 was Intel’s first attempt at 64-bit processing. It was first used in the Itanium processor, released in June 2001. Like EM64T, it is supposed to be a fairly straightforward extension of IA-32/x86 technology to 64 bits. It differs from EM64T, however, in the following ways:
- It runs 32-bit code very poorly. On average, it processes 32-bit code at 1/8 the speed of an equivalent x86 processor.
- It is propriety. Only Intel was able to use the technology; AMD could not.
The standard was in general a failure. Production delays meant that the first chips that implemented the standard were released two years behind schedule. The chip provided very marginal improvements when operating in 64-bit mode, and the lack of backwards compatability (except when running at extremely slow speeds) was a significant drawback.
Microsoft has announced that Windows Vista will not support fully the Itanium processor, and Intel has largely abandoned the design, and reverted back to the Xeon chips that Itanium had originally been slated to be replaced.