The 6x86™ P-Rating

A Performance Indicator for the 6x86 Processor

January, 1996

Published jointly by:
Cyrix Corporation
IBM Microelectronics
SGS-Thomson

Abstract

Throughout the evolution of the x86 microprocessor, clock speed as measured in megahertz and architectural generation (386, 486, etc.) has been the standard indicator for PC users to rate performance. In 1996, however, as multiple CPU architectures emerge in the PC marketplace, clock speed and architecture alone can be inaccurate and inconsistent. By using modern application-based performance benchmarks, it is possible to predict processor performance under real-world conditions. CPU manufacturers Cyrix, IBM Microelectronics, SGS-Thomson and Advanced Micro Devices have worked closely to establish a methodology for a more relevant performance indicator -- the P-rating.

The Ziff-Davis Winstone® 96-based P-rating represents an unbiased measurement of how well a PC runs the most commonly used Windows®-based applications. The PC industry should encourage hardware purchasers to consider the P-rating performance indicator when evaluating the 6x86 processor. This report explains how this new industry performance standard and methodology applies to the 6x86 processor.

Introduction

Over time, processor architecture and clock speed, as measured in megahertz, have become the primary indicators of PC performance. Consumers, business purchasers and manufacturers alike place a great deal of weight on architecture and clock speed to differentiate one system from another.

Impact of New Architecture

The processor architecture and clock speed model works adequately only if Intel processors are being compared. The model fails, however, when it is used to compare x86 processors with different architectures. For example, the Cyrix and AMD 5x86 architectures are different, even though they have the same name (see Table 1). Notice how megahertz can be misleading -- the 120 MHz Cyrix 5x86 processor and the 133 MHz AMD 5x86 are performing in a class that is better than the 90 MHz and 75 MHz Pentium® processors, respectively. Clearly, a PC purchaser would be confused by the name and megahertz labels alone.

Table 1.
=====================================================
                                       Winstone 96
 Company        CPU        MHz         Performance
=====================================================
 Cyrix          5x86       120 MHz     > Pentium 90
-----------------------------------------------------
 AMD            5x86       133 MHz     > Pentium 75
-----------------------------------------------------
 Cyrix          6x86       133 MHz     > Pentium 166
=====================================================

The 6x86 processor faces a similar issue since it achieves higher performance than the megahertz indicates through the use of a more advanced sixth-generation architecture (see Table 2). The integer and FPU pipelines are optimized for maximum instruction throughput by using innovative techniques such as register renaming, out-of-order completion, data dependency removal, branch prediction and speculative execution.

Table 2.
=====================================================
 Architectural Feature            6x86       Pentium
=====================================================
 Full x86 Instruction Set
 Optimization                      X
-----------------------------------------------------
 Superscalar                       X            X
-----------------------------------------------------
 Superpipelined                    X
-----------------------------------------------------
 Register Renaming                 X
-----------------------------------------------------
 Data Dependency Removal           X
-----------------------------------------------------
 Multi-Branch Prediction           X
-----------------------------------------------------
 Speculative Execution             X
-----------------------------------------------------
 Out-of-Order Completion           X
-----------------------------------------------------
 80-Bit FPU                        X            X
-----------------------------------------------------
 16-KByte Primary Cache            X            X
=====================================================

This more advanced architecture means, for example, that the 6x86 processor with a clock speed of 133 MHz actually outperforms the 166 MHz Pentium processor (see Table 1). As the table shows, the architecture and clock speeds are misleading indicators of actual performance when comparing processors that incorporate different architectures.

The P-Rating

The new breed of x86 microprocessors, such as the 6x86 and 5x86 CPUs, are driving the development of a more relevant performance indicator. To make it easier for PC purchasers to understand the performance class of non-Intel CPUs, Cyrix, IBM Microelectronics, SGS-Thomson and Advanced Micro Devices have worked closely to develop an unbiased performance methodology called the P-Rating.

The P-rating indicates to a hardware purchaser how the performance of a specific processor compares to a Pentium CPU when running Winstone 96 in identically configured PC systems.

For the 6x86 processor, a P+ designation is used to indicate better performance.

       Winstone 96 6x86-Pxxx+  >  Winstone 96 Pentium-xxx

               xxx = P-rating or Pentium megahertz

For example, a 6x86 processor with a P-rating of "P166+" (regardless of processor name and clock speed) indicates performance faster than a 166 MHz Pentium processor. The plus mark indicates performance that consistently exceeds the same Pentium processor megahertz level.

Why Pentium?

The Pentium processor was chosen as the reference point for the 6x86 P-rating because it is recognized as the dominant CPU in 1996 based on market share estimates.

Why Winstone 96?

Ziff-Davis Winstone 96 was chosen because it is a real-world, application-based benchmark that contains the most popular software applications (based on market share) that run on a Pentium processor. Winstone 96 also is the most widely used benchmark, and is freely distributed and available.

Winstone 96 runs the following 13 applications available in four categories.

Business Graphics/DTP

Adobe Pagemaker 5.0a for Windows
Corel Corporation CorelDRAW! 5.02E2
Microsoft PowerPoint 4.0c for Windows

Database

Borland dBASE 5.0 for Windows
Borland Paradox 5.0 for Windows
Microsoft Access 2.0c for Windows
Microsoft Works 3.0b for Windows

Spreadsheet

Lotus 1-2-3 Release 5 for Windows
Microsoft Excel 5.0c for Windows
Microsoft Works 3.0b for Windows
Novell Quattro Pro 6.01 for Windows

Word Processing

Lotus Ami Pro Release 3.1 for Windows
Microsoft Word 6.0c for Windows
Microsoft Works 3.0b for Windows
Novell WordPerfect 6.1 for Windows

6x86 P-Rating Methodology

To establish the P-rating for the 6x86 processor, PC systems were shipped to MicroDesign Resources for performance testing. MicroDesign Resources used identical system configurations to compare the 6x86 and Pentium processors (the 6x86 processor can be used in the same motherboard as a Pentium CPU).

Processors

6x86 CPUs at 100, 120, 133 MHz
Pentium CPUs at 120, 150, 166 MHz

Hardware Configuration

Tyan motherboard (Triton chipset) with 512K Synchronous Burst Cache
Quantum Fireball 1080A IDE Disk
Matrox Millennium PCI card, Windows 95 ver. 4.0 driver

Software Configuration*

Default Windows 95 virtual memory settings
1024 x 768 x 256 resolution

* Duplicates testing guidelines as published in PC Magazine, "Top 103 Windows Machines," 12/5/95.

In the 6x86-Pentium comparison, Table 3 shows that the 6x86 processor consistently outperformed higher-frequency Pentium processors on Winstone 96.

Table 3.
=====================================================
 Winstone 96 Results
=====================================================
             100 MHz         120 MHz         133 MHz 
 6x86       -----------------------------------------
                71.7            81.9            86.7
=====================================================
             120 MHz         150 MHz         166 MHz 
 Pentium    -----------------------------------------
                70.9            77.6            82.7
=====================================================

Following the guidelines established by the P+ formula, the 6x86 processor achieves these ratings.

100 MHz -- P120+
120 MHz -- P150+
133 MHz -- P166+

These results support the case for a new performance measurement to supplement actual clock speed.

Intel recognized the performance measurement problem when in 1993 it published a report called, "iCOMP Index, A Simplified Measure Of Relative Microprocessor Performance." The report described the iCOMP Index as "a simple numerical index of relative performance for making straightforward comparisons of Intel CPU power."

Since the time this report was published, however, other manufacturers have achieved significant advances in x86 architecture, and the iCOMP Index is not necessarily applicable to non-Intel processors. iCOMP also uses synthetic benchmarks which have often proven to be misleading in communicating real-world performance to end users. The Winstone 96-based P-rating represents an unbiased measurement of how well a PC runs the most commonly used applications, and it is easily repeatable.

Conclusion

The P-rating communicates the performance of the 6x86 processor relative to the Pentium processor using 1996 market dynamics. It is a clear and accurate method for purchasers of PCs to better evaluate the class of processor they are buying.

The P-rating doesn't abandon architecture and clock speed altogether; it makes those indexes more relevant to actual usage. In the future, this performance methodology rating will be modified to reflect changes in the marketplace, thus giving PC purchasers a performance indicator that continues to be a relevant and useful rating standard.