Competitors have moved away from simply making clones of the Intel processors. They are currently designing their own processors with unique features:
- NextGen Nx586
- AMD AmSx86
- Cyrix 6x86
- IBM 6x86
RISC (Reduced Instruction Set Computing)
Until recently, all the Intel processors had been based on a CISC (complex instruction set computing) architecture. Processors based on RISC (reduced instruction set computing) have been used in high-powered machines since the mid-1980s. Intel has produced its own version of a RISC-based processor that uses a much smaller and simpler set of instructions, greatly enhancing the speed of the processor.
Pentium Pro
Intel made CPU selection even more complex with the introduction of the Pentium Pro, offering varied features, in different models, of the Pentium design. This processor was aimed at a 32-bit server and workstation-level applications such as computer-aided design (CAD), mechanical engineering, and advanced scientific computation. The Pentium Pro was packaged with a second speed-enhancing cache memory chip, and boasted 5.5 million transistors. First available in November, 1995, it incorporated an internal RISC architecture with a CISC-RISC translator, three-way superscalar execution, and dynamic execution. While compatible with all the previous software for the Intel line, the Pentium Pro is optimized to run 32-bit software. Its pin structure and mount differ from the basic Pentium, requiring a special ZIF socket. Some motherboards have sockets for both Pentium and Pentium Pro, but most machines use motherboards designed for one or the other. The package was a 2.46-inch by 2.66-inch 387-pin PGA configuration to house a Pentium Pro processor core and an on-board L2 cache. Although mounted on one PGA device, they are two ICs. A single, gold-plated copper/tungsten heat spreader gives them the appearance of a single chip.
The main CPU and 16-KB first-level (L1) cache consist of 5.5 million transistors; the second chip is a 256- or 512-KB second-level (L2) cache with 15 million transistors. A 133-MHz Pentium Pro processes data about twice as fast as a 100-MHz Pentium.
One reason for the better performance is a technology called dynamic execution. Before processing, the data flow is analyzed and sequenced for optimal execution. Then the system looks ahead in the program process and predicts where the next branch or group of instructions can be found in memory, then processes up to five instructions before they are needed. By using a technique known as data-flow analysis, the Pentium Pro can determine dependencies between data items so they can be processed as soon as their inputs are available, regardless of the program's order.
Pentium MMX
Soon, more choices were on the way. About the time the 166-MHz Pentiums shipped, Intel introduced MMX (multimedia extension) technology, designed to enhance performance of data-hungry applications like graphics and games. With larger data and code caches, Pentiums with MMX technology can run non-MMX-enhanced software approximately 10 to 20 percent faster than a non-MMX CPU with the same clock speed.
To reap the full benefits of the new processor, MMX-enhanced software makes use of 57 special multimedia instructions. These new MMX operators use a technology called single instruction multiple data (SIMD) stream processing. SIMD allows different processing elements to perform the same operations on different data-a central controller broadcasts the instruction to all processing elements in the same way that a drill sergeant would tell a whole platoon to "about face," rather than instruct each soldier individually.
The MMX chips also take advantage of dynamic branch prediction using the branch target buffer (BTB) to predict the most likely set of instructions to be executed.
The MMX Pentium processor is also more compatible with older 16-bit software than is the Pentium Pro; consequently, it soon doomed the Pro to the backwaters of PC computing. All later versions of the Pentium have incorporated some variation of MMX and improved on it. The original Pentium desktop line ended with the 233-MHz MMX release in June of 1997.
