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Intel Copied AMD's 64-bit Chip Designs: Report

Despite the trash talking between Intel and AMD about their 64-bit x86 processor architectures, the chips are "almost, but not quite, identical," according to a new research report.

An independent analysis released last week by In-Stat/MDR even discovered a few differences that even AMD and Intel were unaware of. The report shows that near-100 percent software compatibility is possible, but in some cases, programs written for one 64-bit architecture may not run properly on the other 64-bit architecture.

"Despite the differences, Intel clearly derived its 64-bit architecture by reading AMD's pre-release documentation for AMD64 and by testing AMD64 processors," Tom Halfhill, a senior editor with In-Stat/MDR's Microprocessor Report said in a statement.

Memory-addressing schemes and many other architectural features, such as data-addressing modes, context-switching behavior, interrupt handling, and support for existing 16- and 32-bit x86 execution modes were also compared. In every case, Intel had patterned its 64-bit x86 architecture after AMD64 in almost every detail.

Representatives with Intel and AMD were not immediately available for comment.

"We found nothing to contradict Intel's promise that its 64-bit x86 processors will run the 64-bit operating systems developed for AMD64," Halfhill said. "At the same time, Intel's reluctance to make a blanket guarantee about mutual 64-bit software compatibility is justified by the minor differences we discovered. Of course, that's always the case when Intel or AMD introduces new x86 extensions-such as Intel's SSE3 media extensions, which aren't yet supported by AMD."

While both Silicon Valley-based companies compete head-to-head in the 32-bit space, it wasn't until Intel revealed that it would produce 64-bit software extensions for its Pentium and Xeon processor family that 64-bit really turned into a real horse race.

Whereas AMD had released its 64-bit Opteron and Athlon64 products back in 2003, Intel publicly remained firm on its 64-bit EPIC architecture Itanium platform. During the announcement in January, Intel CEO Craig Barrett said overall, software should be able to run on either x86-based architecture.

"The software will run on both systems for the most part. There will be some different things that our chips will have, but we'll make sure that people can write for it," Barrett told attendees at Intel's Developer Forum at the time.

Some of the differences could be resolved in future 64-bit x86 processors, or even in future steppings of the x86 processors already on the market, Halfhill said. In other cases, software could easily adapt to the differences by executing slightly different code, after first probing the CPU to learn which 64-bit extensions it supports.

"Intel's reverse-engineering of AMD64 marks a major turning point in the historical relationship between the companies," says Halfhill. "Although AMD has in the past introduced some innovations to the x86 architecture -- the 3DNow multimedia extensions being a prime example -- this is the first time AMD has truly steered the direction of the world's most important microprocessor architecture, which Intel invented in 1978 and has closely guarded for 26 years."

AMD was first to jump on this by marketing AMD64 as its version of x86 architecture running on 64-bits (generically known as x86-64) for its Opteron and Athlon processors. Intel has taken a different path, picking Intel Extended Memory 64 Technology -- or Intel EM64T -- as its moniker for its 64-bit extension technology (previously code-named Clackamas Technology or "CT").

Both the Opteron and Athlon 64 boast 64-bit data and address paths and breakthrough current 32-bit CPUs' 4GB memory addressing cap with 40-bit physical (up to 1 terabyte) and 48-bit virtual (up to 256 terabytes) memory addressing space. The Opteron also supports three HyperTransport links, providing up to 19.2GB/sec of bandwidth, versus the Athlon 64's single HyperTransport link for 6.4GB/sec of data transfer.

In terms of architectural changes, the most noticeable is the Opteron's integrated memory controller -- a 128-bit, dual-channel design supporting DDR266 and DDR333 SDRAM.

Both the Opteron's memory controller and the Athlon 64's -- a single 72-bit channel -- take that job away from its traditional place in the system chipset's external Northbridge, greatly reducing the latency of read/write requests. This essentially controls the system at, or yields a front-side bus speed matching, the clock speed of the CPU.

This year, a 0.13-micron-process silicon-on-insulator Opteron -- a 90-nanometer-process successor -- will arrive. That chip will feature two more pipeline stages than AMD's Athlon XP; instructions-per-clock-cycle boosters such as enhanced branch-prediction algorithms and larger translation look-aside buffers; support for the SSE2 streaming multimedia instructions that debuted in Intel's Pentium 4; and up to 1MB of Level 2 cache, all in a new, plus-sized processor die or 940-pin ceramic package. (The Athlon 64 will use a different 754-pin socket.)

Intel said its EM64T will be included in its upcoming single-processor and dual-processor IA32 server and workstation products (code named Prescott and Nocona). The company said it will bundle several features into these chips including its Hyper-Threading technology, PCI Express, DDR2 support, enhanced power management, SSE3 instructions, high-definition audio, faster bus speeds, faster frequencies, enhanced security (LaGrande) and virtualization (Vanderpool) technologies.

In separate announcements, both Intel and AMD released software tools that would let developers optimize their software

Intel said version 8.0 of its Fortran Compiler, Professional Edition, for Windows is now available. The software includes the Intel Visual Fortran Compiler, Array Visualizer, Code Coverage Tool, Test Prioritization Tool and the Debugger.

Meanwhile, AMD announced the free availability of its AMD Core Math Library (ACML) version 2.0, an advanced tool co-developed with the Numerical Algorithms Group (NAG). The software tool helps developers increase performance of Basic Linear Algebra Subroutines (BLAS) and Fast Fourier Transform (FFT) routines from version 1.5.



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