Friday, July 27, 2007

How Will MMX Affect CAD Performance? (01mar97)

March 1, 1997

A new wave of Pentium PCs is currently hitting the market using Intel microprocessors that incorporate an expanded instruction set called MMX (MultiMedia eXtension). Although the correct name for these chips is the P55C, don’t expect to see that used very much. Everyone will refer to these systems as simply being MMX-based. The technology is also being offered (via licensing) in microprocessors sold by Cyrix and in the near future, by Advanced Micro Devices.

MMX adds 57 new instructions to the traditional x86 architecture. These instructions are tuned to enhance the type of arithmetic operations that commonly occur in video, audio, and similar applications. That’s why these instructions carry the multimedia nomenclature. The big question is what does this mean to users of typical engineering design software? It turns out that at a given clock speed, these systems will function 10% to 20% faster, but not because of the MMX instructions. Performance for the 200-MHz chip is 6.4 SPECint95 and 4.7 SPECfp95. This is comparable to what Silicon Graphics offers with a R5000/180SC O2 workstation.

Intel did more than just add new instructions when it redesigned the Pentium microprocessor. The company doubled the size of the internal cache memory to 32 KB and redesigned some of the chip’s internal logic. This is the major reason for an increase in general system performance.

Improved Graphics Performance

Eventually we will see substantial improvements due to MMX in visualization and animation packages, (such as VisFly, Lightscape and 3D Studio MAX), when these programs are re-compiled to incorporate MMX instructions. That could be in late 1997 or beyond, depending upon customer demand and competitive pressures. The use of MMX instructions could result in a 50% or better performance improvement for some functions.

One of the problems facing developers of technical applications is that the MMX instructions conflict with the execution of traditional floating point operations. Programmers need to be careful to clearly segment the two types of computing and to ensure when one program takes over the machine from another in a multi-tasking environment, that the program understands what execution state the system is in. This is properly done by the operating system, but we have not heard of anything Microsoft is doing with Windows 95/97 or Windows NT 4.0 to mitigate the problem.

Future Pentium Developments

By mid-year, Intel will be offering MMX capability with its Pentium Pro microprocessors. Known as Klamath, it will incorporate internal cache and other architectural changes as well as come in faster versions. Our understanding is that these will initially run at speeds up to 266-MHz compared to the current 200-MHz maximum. Vendors, such as IBM, plan to offer Klamath-based machines shortly after Intel releases this new microprocessor.

Most PC vendors have already switched over to MMX Pentiums for their mid-range 166-MHz and 200-MHz systems and, as far as we can tell, customers are paying little, if any, premium for these machines. By mid-year, Intel will also be shipping 233-MHz MMX-enabled Pentiums.

For the past year or so, we have been concerned that Intel was falling behind in the raw speed aspects of microprocessor manufacturing. While companies such as Digital were pushing 500-MHz, Intel was stuck in the 200-MHz range. We realize that Digital’s Alpha and the Pentium or Pentium Pro cannot be compared strictly on a clock cycle basis, but clock speed does say something about how advanced a company’s manufacturing capability is.

Intel sought to set these fears to rest recently when it disclosed that it had Pentium Pro microprocessors running at up to 451 MHz in the laboratory. Moving from the laboratory (at 451 MHz, the Pentium Pro requires an ice-water heat sink) is not a simple step but we are comfortable in expecting 300-MHz Klamath systems by the end of this year and 400-MHz systems in 1998.

Finally, we recommend that users move cautiously when implementing MMX-enabled software in a design environment. What works well for playing games might cause problems in the design office. If you need more performance and can wait several months, you might want to see how Klamath turns out in this regard before you buy additional Pentium Pro systems.