The Processors (continued...)

The Pentium
With Intel's fifth generation of processors came a new name, the Pentium. Everyone, including the competition, expected the new chip to follow the same typical naming convention they had used for years, but Intel had different ideas. Instead of naming the chip the "586", they gave it a name that they could copyright. The name Pentium implies '5' and, maybe at first was just a name for their fifth generation of processors, but it's become a trademarked brand name, associated with Intel only, and continued throughout their later processors to today.

The original Pentiums (code named P5) borrowed a lot from the RISC processors. It uses superscalar technology, which is like having two processors in one. Intel developed a technology that could split up the program code. With multiple pipelines providing two separate program paths, the CPU can be processing two separate pieces of code at the same time. At times, this can allow for more than one instruction to be processed in a single clock cycle.

Intel's biggest problem was feeding data to the chip fast enough. They kept the pipelines full by doubling the width of the data bus from 32-bit to 64-bit, and increasing the clock speed from 33MHz to 66MHz. The expansion bus, with its own multiplier set at 0.5, still ran at 33MHz. The first two models ran at 60MHz and 66MHz (the 60MHz CPU had a 60MHz bus speed). The 66MHz Pentium had cooling problems and the Pentium 60 was much more reliable. By lowering the voltage to 3.3Vdc from 5Vdc, and taking advantage of newer micro-technology, Intel set the internal multipliers at 1.5 and increased the Pentium's internal speeds to 90 and 100 MHz.

There were many versions of the Pentium as a fifth generation processor. Newer processes and technologies allowed the P54C speeds from 133 to 200 MHz. The P55C was introduced in 1997 with approximately 72 new instructions that were targeted towards enhancing the performance of the graphics, audio, and animation involved in multimedia computing. Named the Pentium MMX (MultiMedia eXtensions), what most people didn't know at the time, was that it didn't have any affect on multimedia programs unless they were specifically written to take advantage of the new instruction set. What did improve performance, however, was increasing the size of the internal cache (L1) from 16K to 32K. The internal clock speeds for the MMX were150, 166, 200, 233 and 266 MHz.

Pentium Pro
The Pentium Pro (code named P6) began the 6th generation of processors from Intel. It doesn't include MMX technology, but what it does offer is a true RISC core. It has internal translation circuitry that can decipher the CISC instruction set into smaller sets that the RISC core can understand. Another characteristic of this 6th generation chip is an internal secondary cache of 256K.

It was discovered with the 486 that a small, internal primary cache (L1) of very fast SRAM placed right inside the CPU, with a faster and wider connection, increases the system's overall performance. It only makes sense then, that if you can place the secondary cache inside the processor, it would also increase performance.

That's what Intel did with the Pentium Pro. The only problem was that the number of circuits required for 256K of cache was just about as many as the CPU itself needed. All these circuits could not fit on the same piece of silicon. So they embedded two pieces of silicon (or substrate) inside the same chip and connected the CPU to the secondary cache with a dedicated 64-bit bus they called the "backside bus".

The new chip was no longer square like the previous processors, but rectangular, and about twice as wide. The chip required a new (socket 8) socket, but the speed of the secondary cache was now the same as the internal speed of the processor.

The most popular P6 chips ran at 166MHz and 200MHz. They had a 64-bit internal data bus and could access up to 64GB of memory (once again however, the chipset technology only allowed 512 MB on the motherboard).

The Pentium Pro's ability to translate CISC commands to RISC uses 32 bit logic circuits. It worked very well on the newer 32-bit programs, but was a real dog with early versions of Windows 95 and the older 16-bit software. For this reason it wasn't a good choice for the typical home computer and was used mainly in network servers.

continued...