MMX - A Diamond Multimedia White Paper

MMX is the first major change to the x86 processor architecture since 1985. MMX consists of 57 new instructions to accelerate common multimedia functions. MMX enabled Pentium processors from Intel are expected to be available in early 1997 and will be either 166 MHz, or 200 MHz devices. By the end of 1997 all new processors from Intel will have MMX.

An MMX Pentium processor is between ten to twenty percent faster than a non-MMX Pentium, even without any of the MMX functions being used. This is because Intel has redesigned the Pentium to accommodate MMX, and optimized some of its base architecture in the process. For any performance benefits to be realized from the use of MMX functions, you need software specifically written to work with MMX. Intel adopted MMX to increase the performance of its processors in today's multimedia computing environment, but the design makes no sacrifices in terms of existing operating system and application requirements. Therefore, users of MMX systems should expect to see their non-MMX applications work as they always did on the new processors.

However, many MMX applications will be available when the platform launches. Only software written specifically to use MMX functions will provide enhanced performance, as a result, many telephony, communications, and digital video products are being modified to use MMX. With Microsoft incorporating MMX technology in their DirectX APIs, a number of entertainment software titles will also be available as MMX enabled systems begin to reach customers. MMX is, thus, an enabling technology which helps to raise the overall performance of multimedia applications.

How MMX Works

MMX uses the existing registers of a Pentium processor, which are presently used to store Floating Point data. Intel has provided a mechanism whereby software developers can take these existing eight Floating Point registers, and toggle them to allow their use for MMX data. This procedure, in effect, creates eight new registers for the software developer without in any way effecting the existing registers. Therefore, Floating Point and MMX functions cannot be used together. Floating Point data is essential in calculations relating to 3D graphics, while MMX data can only work in an integer mode.

There is a mistaken assumption that MMX increases 3D graphics performance. This would only be true for situations where 3D graphics acceleration is not available. By the time MMX is available, 3D graphics acceleration will be widely available on most graphics boards. Where 3D graphics acceleration is not available, MMX functions may be used to increase rendering performance, but not calculations relating to 3D geometry. Triangle set-up, a complex geometry calculation in 3D, will be available as a feature of 3D graphics controllers in 1997.

Where MMX really shines is in the use of Single Instruction, Multiple Data (SIMD) operations. MMX can handle data in a variety of formats, 57 to be precise. Intel has achieved this by splitting the 64-bit bus on the Pentium into three combinations of data. These data types are 8 byte-sized words, four 16-bit words, and two 32-bit double-words. SIMD allows a stream of data of multiple bytes to be acted on by a single command. In the case of digital video, such as MPEG-2, information for each frame is different, but the decoding of the information is basically the same operation. The same is true of audio, such as the AC-3 multi-channel standard, where each byte of sampled audio is acted on by the same instruction. Audio data is sampled at the different rates producing either 8, 12, or 16 bit words, which are easily handled by MMX SIMD in a parallel means. Therefore, MMX enabled processors with SIMD handle digital audio and video streams better than non-MMX processors.

There is a drawback to MMX processors being burdened with digital video and audio decoding because CPU processing cycles are still taken up at the expense of the application. Furthermore, hardware assistance is required to ensure digital video can be scaled, and color conversion takes place between video YUV to RGB format. MMX processors will, thus, provide base level support of MPEG-2 video, and AC-3 audio, but hardware assisted playback will still play an important role in multimedia acceleration on MMX PCs.

Diamond's MMX Strategy

Multimedia functionality and performance helps to define the use of a PC. Low cost PCs, such as the NetPC initiative from Microsoft and Intel, sit side-by-side with powerful multimedia workstations. These machines all share the same Windows applications, but require differing levels of functionality. MMX is a cost effective entry level multimedia accelerator for the low-end PC solution, but offers an added driver boost to hardware accelerated multimedia systems. Diamond recognizes both the strengths and the shortcomings of MMX, and the company's products will MMX to increase the overall performance of multimedia applications. The higher performance of MMX processors overall will be reflected in better performance from Diamond's multimedia accelerators because they are designed to scale up with increases in processor performance.

Diamond believes MMX will enable new multimedia applications to be developed for a broader range of PC users. MMX will also help to establish higher performance levels for multimedia accelerators. Diamond's drivers are being designed to take into account the enhancements MMX brings.