Step 6 Computer Processing Needs

On an average, computation power doubles every 18 months—a trend that has become known as Moore's law. This translates to an annual 67% increase in computing power. Since 1990, the growth in storage capacity has been outpacing Moore's law by a wide margin, advancing 12 times faster than processing speed (29). Data transmission technology has developed at a more modest rate with a 50% annual increase in bandwidth (Nielsen's law). Enormous amounts of data can now be processed in milliseconds and graphical rendering is approaching photorealism. High-end graphical applications use to require expensive workstations with a price tag greater than $50,000. Now the same performance can be achieved on a personal computer that costs less than $2000. All of this has lead to remarkable advances in virtual reality and the improvements have not gone unnoticed by the medical community.

The processing power required for different simulators will vary because each simulated procedure will require different levels of graphical rendering, collision detection, deformation modeling, and haptic feedback. Processing power will directly affect latency and frame refresh rate.

Latency is a measure of the time between when a person moves a tracking device and when the computer displays the result of that tracking on the video screen. As latency exceeds 1/10th of a second, most people will become distracted by the disconnection between their actual movement and what they see moving graphically.

Frame refresh rate refers to the number of still images displayed per second. When the frame update rate is less than 20 frames per second, most people will perceive animation as jumpy or flickering. When displaying stereoscopic images (three-dimensional projections), the refresh rate needs to be at least twice as high to achieve smooth animation.

When considering processing power, one needs to consider not only the central processing unit but also the processing power of the graphics card. If the processing power of either is too low, the likely result will be extended latency and low refresh rates. The bus speed of a processor refers to the speed at which it can import and export data. Processing speed can become irrelevant if it takes too long to transfer data to and from the processor. Similarly, the speed of computer memory (or RAM) can create a performance bottleneck. To a lesser degree, the speed of hard drive storage can also affect performance. Finally, for computationally intensive applications, it can be very advantageous to use multiprocessor systems that divide processing labor between multiple processors and perform computations in parallel.

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