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  Transmeta's Crusoe, HotRod or Performance Hog? 
  May 11, 2001, 06:00am EDT 


By: Sander Sassen

Upon introduction Transmeta's Crusoe processor has generated much interest with its promises of strong performance and long battery life. This, in combination with announcements from well-known manufacturers that they will incorporate Transmeta's processors in their notebooks, has led many people to believe that we'll see substantial improvements in price/performance levels for these devices.

In actuality Transmeta has developed a whole new approach to microprocessor design, and not just another processor. Currently an entire processor with the accompanied instruction set is implemented in hardware (for example a x86 processor such as the Intel Pentium III), and then the software is written specifically to make use of that instruction set. Transmeta chose to do it differently; rather than implementing the entire x86 instruction set of the processor in hardware, the Crusoe processor consists of a compact hardware engine surrounded by a software layer.

The hardware component is a very simple, high-performance, low-power VLIW (Very Long Instruction Word) engine with an instruction set that bears no resemblance to that of x86 processors. Instead, it is the surrounding software layer that gives programs the impression that they are running on x86 hardware. This innovative software layer is called the Code Morphing software because it dynamically translates or rather 'morphs' x86 instructions into the hardware engine's native instruction set.

This unique approach to executing x86 code eliminates millions of transistors, replacing them with software. For example, the current implementation of the Crusoe processor uses roughly one-quarter of the logic transistors required for an all-hardware design of similar complexity. Apart from the obvious reduction in cost, this approach has the following benefits:

The hardware component is considerably smaller, faster, and more power efficient than conventional processors. The hardware is fully decoupled from the x86 instruction set architecture, enabling Transmeta's engineers to take advantage of the latest and best in hardware design trends without affecting legacy software.

The Code Morphing software can evolve separately from hardware. This means that upgrades to the software portion of the microprocessor can be rolled out independently of hardware chip revisions. Transmeta's Code Morphing technology is obviously not limited to x86 implementations.

However, software routines usually aren't as fast as a hardware solution, even when coded in assembly, the processor's native programming language. In the following pages we hope to give you some insight into the Crusoe's workings and analysis of prospective performance.

1. Introduction
2. Code Morphing
3. Execution, Decoding, Scheduling
4. Caching and Optimization
5. Power Management
6. Conclusion

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