CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [75]
Figure 5-38 shows a more modern configuration, labeling the important buses. Note that the external data bus and address bus are there, but the chipset provides separate address buses and external data buses—one set just for the CPU and another set for the rest of the devices in the PC. No official name has been given to the interface between the RAM and the chipset. On the rare occasions when they discuss it, most techs simply call it the RAM interface.
Figure 5-37 A P6 opened to show separate CPU and L2 cache (photo courtesy of Intel)
Figure 5-38 Frontside and backside buses
The Pentium Pro had a unique PGA case that fit into a special socket, called Socket 8. No other CPU used this type of socket. The Pentium Pro made strong inroads in the high-end server market, but its high cost made it unacceptable for most people’s desktop computers.
Although the Pentium Pro never saw a large volume of sales compared with the Pentium, many people in the industry consider it the most important chip ever created by Intel. Its feature set was the prototype for all CPUs designed ever since.
Later Pentium-Class CPUs
Intel’s usual game plan in the rough-and-tumble business of chip making is to introduce a new CPU and simultaneously declare all previous CPUs obsolete. That did not happen with the Pentium Pro, however, because Intel never really developed the P6 for most users. It was to be the CPU for powerful, higher-end systems. This kept the Pentium as the CPU of choice for all but the most power-hungry systems.
Figure 5-39 Later-generation Pentium
While the Pentium Pro languished on the high end for several years, Intel and AMD developed new Pentium-class CPUs that incorporated a series of powerful improvements, some of which were taken from the Pentium Pro. These improvements required that they be regarded as a new family of CPUs, which I call the “later Pentium-class CPUs” (Figure 5-39). Although certainly some profound differences exist between these CPUs, they all have three groups of similar improvements: multimedia extensions (MMX), increased multipliers/clocks, and improved processing.
Later-generation Pentiums were pin-compatible with earlier Pentiums, but included a large number of improvements. The most important improvement was increases in multipliers, and therefore clock speeds, but other improvements also took place—some borrowed from the P6 and some developed just for this new breed of Pentium.
MMX
In 1996, Intel added a new enhancement to its Pentium CPU, called multimedia extensions (MMX), in response to the large number of programs with heavy graphics needs coming out at this time. MMX was designed to work with large graphics by calculating on large chunks of data and performing vector math (vector math is needed to handle graphical issues such as spinning a 3D object). MMX was not heavily supported by the folks who wrote graphics programs, but MMX did start the idea that CPUs should have special circuitry just for such programs. Over time, the graphics community began to work with Intel to improve MMX, eventually replacing it with better solutions.
Increased Clocks and Multipliers
Later Pentiums all have vastly increased multipliers, resulting in higher speeds. Most early Pentiums used 2.5× multipliers at best, but later Pentium-class processors had up to 4.5× multipliers.
Pentium II
Intel’s next major CPU was the Pentium II. Although highly touted as the next generation of CPUs, the Pentium II was little more than a faster Pentium Pro with MMX and a refined instruction set. The Pentium II came in a distinctive single-edge cartridge (SEC) that gave more space for the L2 cache and made CPU cooling easier while freeing up more room on the motherboard (Figure 5-40). Aggressive