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Material Type: Paper; Professor: Grevera; Class: Modern Computer Architecture; Subject: Computer Science; University: Saint Joseph's University; Term: Unknown 1989;
Typology: Papers
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The need for 64-bit computing is driven by applications that address large amounts of data and memory, such as high-performance servers, database management systems, CAD tools, and digital content creation tools. Although this increased demand on the high-end along with technical advances is making 64-bit a reality, it is anticipated that the industry as a whole will not fully embrace the 64-bit world entirely for many more years.
Existing 32-bit environments and applications will continue to serve a majority of users for quite sometime, although they too will require continual improvements in processor and system performance to continue. Many x86 workstation and server users are now facing the dilemma of how to transition to 64-bit computing, yet maintain their existing knowledge base and investment in the existing code base and tools. The challenge for processor manufacturers is to find a way to offer customers all the advantages of 64-bit processing in a market friendly fashion while making the conversion from 32-bit efficient and inexpensive. Unfortunately, the 64-bit solutions proposed by some processor manufacturers leave customers facing a potentially disruptive and ultimately expensive transition to the new architectures.
AMD's strategy of extending the x86 architecture for 64-bit computing is a straightforward alternative to total conversion using incompatible instruction sets. AMD processors including the x86-64TM^ technology will permit platform suppliers, developers, corporate MIS departments and consumers to transition to 64-bit environments gradually, while continuing to run 32-bit applications without incurring performance penalties. By providing a smoother migration to 64- bit computing, AMD's strategy is designed to save its customers billions of dollars in software re-development and deployment costs.
Better Solution: AMD x86-64 Architecture
While 64-bit computing may offer vital features for some applications, the transition from 32- to 64-bit raises notable issues for several audiences:
To date, processor manufacturers have attempted to solve some of these transition issues with less than satisfactory results. Software emulation provides 32-bit compatibility but lacks native performance. And requiring the user to purchase and install a separate, 32-bit co-processor entails additional investments in money and administration.
New 64-bit VLIW-based (Very Long Instruction Word) architectures, such as Intel’s IA-64, force users to undergo a laborious transition process to a new instruction set to achieve full native performance. This is because IA-64 offers no native x86 compatibility, which means existing 32-bits applications are not anticipated to run with leading edge performance on IA- technology based processors. Also, the adoption of an entirely new instruction set architecture like IA-64 requires the development of an entirely new tool chain including compilers, debuggers, assemblers, and profilers, whereas x86-64 tools can be modified from existing code.
AMD’s 64-bit strategy is one that allows the latest in processor innovation to be brought to the existing installed base of 32-bit applications and operating systems, while establishing an installed base of systems that are 64-bit capable.
It is also the only solution that allows companies and individuals to enable 64-bit computing at their own pace, as hardware and software support becomes available. This allows the industry to advance software development on all fronts, with x86 compatibility, while providing the capability of delivering 64-bit performance benefits. Any other 64-bit solution does not fully preserve the industries investment in software.
AMD takes a more practical and less disruptive approach to the challenge of 64-bit computing. Key extensions to the reliable, proven, high-performance x86 instruction set not only preserve full compatibility between 32- and 64 bit environments, they also enable 32-bit applications to move up the performance ladder right along with other advances in technology.
AMD does not intend to force its platform suppliers, software developers, and enterprise customers to make the tough choice between protecting their investments in 32-bit technology and moving into the 64-bit world of the future. Instead, AMD's strategy of forward compatibility and future performance allows customers to continue using 32-bit applications and then seamlessly transition to 64-bit when they are ready, and hardware and software support becomes available.
This strategy enables AMD and its platform partners to leverage the latest in 64-bit microprocessor innovations without disrupting their current 32-bit installed base. For operating system and application providers, development can continue uninterrupted and unburdened by transition issues and support for the 64-bit extensions in the x86-64 technology can be provided at their own pace. In addition, the AMD x86-64 architecture permits existing 16- and 32-bit x code to take full advantage of all the performance advances of new processor designs without the overhead of software or hardware emulation.
TM
Fully x86 compatible. Instruction sets are NOT x86 compatible.
No performance sacrifice for either 32-bit or 64-bit computing
Compromises 32-bit performance. Smaller, less sophisticated, x86 engine causes speed penalty for legacy code. Future development is focused on 64-bit only performance.
Not forced to move to a new architecture. Seamless transition based on user's timeframe.
Forces the costly transition of many 32-bit applications that do not require 64-bits.
Continued use of existing 32-bit applications, tools, and knowledge base.
Doubles investment: 2 instruction sets, 2 operating environments, 2 application binaries, 2 development and support teams.
Full support for 16-, 32-, and 64-bit applications running concurrently.
Support for 16- and 32-bit apps only through emulation software or hardware.
32-bit code runs unchanged. Designed to be easy to port applications that might benefit from 64-bit address space.
Must port 32-bit applications for full speed execution. During transition years, must manage 2 code bases.
TM
The AMD x86-64 architecture extends the legacy x86 architecture by introducing two major features: a 64-bit extension called long mod e, and register extensions.
Long Mode Long mode consists of two sub-modes: 64-bit mod e, and compatibility mod e. Compatibility mode supports binary compatibility with existing 16-bit and 32-bit applications under a 64-bit operating system. In addition to long mode, the architecture also supports a pure x86 legacy mod e, which preserves binary compatibility not only with existing 16-bit and 32-bit applications but also with existing 16-bit and 32-bit operating systems.
64-Bit Mode 64-bit mode supports the following new features:
The default address size is 64-bits, and the default operand size is 32-bits. The defaults can be overridden on an instruction-by-instruction basis using prefixes. A new REX prefix is introduced for specifying 64-bit operand size and the new registers. The mode is enabled by the operating system on an individual code-segment basis.
The new register extensions added via the new REX prefix add eight 64-bit GPRs (R8–R15), eight 128-bit Streaming SIMD Extensions (SSE) registers (XMM8–XMM15), and widens all GPRs and the instruction pointer to 64 bits. The REX prefix also provides a new byte-register capability that makes the least-significant byte of any GPR available for byte operations. This results in a uniform set of byte, word, dword, and qword registers better suited for a compiler’s register allocation.
The instruction pointer is also widened to 64 bits.
Because 64-bit mode supports a 64-bit virtual-address space, it requires a 64-bit operating system and tool chain. A few instruction opcodes and prefix bytes are redefined to allow the register extensions and 64-bit addressing.
access the first 4GBytes of virtual-address space. Standard x86 instruction prefixes toggle between 16-bit and 32-bit address and operand sizes.
As with 64-bit mode, compatibility mode is enabled by the operating system on an individual code-segment basis. Unlike 64-bit mode, however, x86 segmentation functions normally, using 16-bit or 32-bit protected-mode semantics. From the application’s viewpoint, compatibility mode looks like a legacy x86 protected-mode environment. From the operating system’s viewpoint, address translation, interrupt and exception handling, and system data structures use the 64-bit long mode mechanisms.
Legacy Mode When LMA=0, the processor is said to be running in legacy mode. None of the 64-bit features are available and the processor operates as a standard x86 processor. Legacy mode is completely compatible with existing 32-bit implementations of the x86 architecture. This includes support for current technologies like segmented memory, and 32-bit GPRs and instruction pointer.
Already performance-leaders for high-volume markets, AMD processors set a clear path for 64- bit processor architectures. Key data and address paths are already 64-bits wide. The x86- architecture is designed to have minimal impact on processor die size and no impact on the progression of processor clock speed. Future improvements in the processor core will accelerate both 32-bit and 64-bit applications. Thus, high-performance systems using 64-bit capable processors from AMD are planned to also be among the highest performing 32-bit systems ever built.
AMD is currently collaborating with its key platform suppliers, operating systems providers, and other technology partners for the x86-64 architecture. AMD plans to include 64-bit technology in its next-generation of performance-leading processors code-named “Hammer” to establish an initial base of 64-bit platforms by the end of 2001.
By extending the x86 core rather than replacing it with a new, entirely different instruction set, AMD makes the transition to a 64-bit world easier, faster, and less expensive for its system partners, developers, and end-user customers. The burden of transitioning to a new architecture is greatly reduced, without limiting the forward compatibility and future performance of existing applications. For platform suppliers and operating systems providers, AMD's x86-64 strategy helps preserve investments in current technology and engineering expertise. Further more, because end-user customers are not faced with a major computing transition, they are anticipated to less likely consider changing their preferred hardware or OS vendor. Offering a solution that provides both compatibility and future performance is a win-win for both suppliers and customers.
For application developers and MIS managers, AMD's strategy allows development to continue on a path of high performance and optimal functionality, regardless of whether the underlying architecture is 32- or 64-bit. Familiar tools, applications, and management protocols are retained until they choose to migrate and hardware and software support becomes available. When they do make the transition, they can do so with a minimum investment of time and resources. AMD's x86-64 strategy brings the latest processor innovation to existing 32-bit environments while establishing a clear path for record-breaking levels of performance, scalability, and compatibility.
History is filled with examples of processor revolutions that never were; transitions to new instruction sets so expensive and time consuming that advances in existing architectures passed them by. Advanced Micro Devices will continue to lead the way by advancing the performance and scalability of x86-compatible processors.
