QuickRing Architecture Could Revolutionize Data Transfer
By Bruce Schneier
June 15, 1992
The QuickRing architecture, announced last month at the Apple Worldwide Developers Conference in San Jose, Calif., could have a profound effect on many areas of high-end Macintosh computing, such as video processing and high-speed networking.
QuickRing is a communications system that lets plug-in NuBus cards exchange data with each other or external equipment at rates of up to 200 Mbps. This is more than 10 times faster than non-burst-mode speeds available in the existing NuBus architecture and opens the door to new applications that Mac developers could only dream of before.
"This is not a NuBus replacement," said Paul Sweazey, Apple QuickRing project manager. "NuBus is a control bus for memory access. QuickRing is a high-speed, point-to-point data transfer system."
QuickRing was designed by Apple's Advanced Technology Group to handle the high-bandwidth needs of video manipulators, but networks beyond today's 10-Mbps and 16-Mbps ranges might need similar throughput.
How does it work? The QuickRing hardware, which will be built into cards, consists of a controller chip from National Semiconductor of Santa Clara, Calif., and a special high-speed connector developed by Beta Phase Inc. of Menlo Park, Calif.
"We've provided Apple with an enabling technology, a simple and elegant solution for a complex problem," said Chuck Byer, general manager of Beta Phase.
"When you need to go at Mach 1, you can get on QuickRing. When you can travel by steamship, you can stay on NuBus," he said.
QuickRing attains its high speeds mainly by abandoning the backbone configuration of a traditional bus in favor of a twisted ring and by using the Beta Phase connectors. The resulting design dramatically reduces the electrical artifacts in the connections between cards, and the higher-integrity signal makes higher throughput possible. The actual data path of a QuickRing connection is just six bits wide, controlled by silicon that signals at 50 MHz.
The control protocols in NuBus that ease the installation and use of cards add a small overhead that reduces data transfer speeds. QuickRing has its own protocol overhead and a higher latency time, but the design is optimized for communication between adjacent cards that run very fast. Each extra card "hop" reduces throughput, especially if the intermediary card is transferring its own data over QuickRing.
"NuBus does too much. There is no way Apple could have modified it for this kind of high-speed data transfer application," said Mike Bentley, president of Crenelle, a Macintosh real-time software-development firm in Chicago.
Initial QuickRing applications undoubtedly will focus on digital video and multimedia, which are the tasks for which the alternative bus was designed.
"The bandwidth on NuBus has been insufficient to handle media-rich data. QuickRing is essential for the Macintosh to process media-rich data while keeping the rest of the computer running," said David Baron, associate editor of Digital Media, published by Seybold Publications Inc. of Media, Pa.
For instance, a single uncompressed, eight-bit, 640-by-480-pixel image -- one screenful from an Apple 13-inch color monitor -- takes up 300 Kbytes. Same-size digital video at 30 frames per second would require a data transfer rate of 9 Mbytes per second; step up to 24-bit color and you need a data rate in excess of 27 Mbytes per second -- faster than NuBus can sustain.
All the proposed U.S. standards for high-definition television, which will include simultaneous sound channels, will require greater bandwidth.
The sheer volume of information to be processed precluded use of Macs in real-time video applications. Instead, users turned to external video-processing boxes controlled by Macs. Or they had to process all-digital video off-line, using gigabytes of disk space to store intermediate results and suffering long data transfer times when moving data in and out of memory.
"QuickRing will let you process studio-quality video in real time, and then display or store it only in its final form," Bentley said.
"It is no longer an issue whether you can get the data there in time, but whether you can process it before the next piece of data gets there," he said.
"There are a class of problems that couldn't be addressed by the Macintosh because there was no way to move the data around fast enough," Bentley said. This area of work includes multiprocessing and real-time data collection and analysis.
In multiprocessing, different processors work on pieces of a large problem; each processor does its work before passing the intermediate results downstream to another processor. The different processors need a fast means to talk with each other, and for many applications, the limit on the multiprocessing system is the bandwidth of communications.
"Performance is limited by the bus architecture. You hit against a brick wall," Bentley said.
If QuickRing remains a Mac-only specification, users also could run into the brick wall of incompatibility. However, the high-speed network could attract other multimedia platforms.
Multiple card vendors could comply to the same communications standard, providing users with more options for creating multiprocessing systems. "You [could] join cards from different vendors and only put in the capabilities you require," said Seybold's Baron.
Some developers expect QuickRing to catapult the Mac into the world of real-time computing and embedded systems.
"Suddenly the Macintosh, which is inherently a non-real-time architecture, can now branch off into data manipulation and scientific applications," said Ron Schreiner, president of Ronsat Technologies, an embedded-system company in Buffalo Grove, Ill.
Developers long have considered the Macintosh an inadequate machine for embedded systems and process control. The Mac operating system is designed to be controlled by a user rather than automated. Also, the hardware is built so that networks and other devices can interrupt processing at a low level. This means desired processes, such as data collection, might not happen exactly when the programmers intended. The way around these limits is to design NuBus cards that control processes independently of the main Mac CPU.
Here again the problem of bandwidth rears its head. Real-world processes tend to generate a lot of information when sampled digitally. "QuickRing means that the Macintosh is no longer constrained by NuBus speeds to transfer information to and from the outside world," Schreiner said.
However, Bentley cautioned: "I don't think that QuickRing alone will cause embedded-systems developers to jump off the PC and onto the Macintosh. There are still problems with the lack of direct memory access and the performance of a Macintosh in an embedded environment. Using QuickRing, the Macintosh can act as a graphical window into a real-time embedded system."
When can you buy it? QuickRing hardware components will not be available to hardware developers until early 1993, so products that use QuickRing are a ways off. Even so, developers and industry observers are reacting to the QuickRing specifications with excitement.
"High-speed links between multiple CPUs is the wave of the future; it is absolutely necessary for processors to communicate at their native speeds for effective multiprocessing," said Ronsat's Schreiner.
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