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Table 3.3 lists the primary specifications for the Intel family of processors used in IBM and compatible PCs. Table 3.4 lists the Intel-compatible processors from AMD, Cyrix, NexGen, IDT, and Rise.
NOTE
Note in Table 3.3 that the Pentium Pro processor includes 256KB, 512KB, or 1MB of full-core speed L2 cache in a separate die within the chip. The Pentium II/III processors include 512KB of 1/2 core speed L2 cache on the processor card. The Celeron, Pentium II PE, and Pentium IIIE processors include full-core speed L2 cache integrated directly within the processor die. The Celeron III uses the same die as the Pentium IIIE, however half of the on-die cache is disabled, leaving 128KB functional.
The transistor count figures do not include the external (off-die) 256KB, 512KB, 1MB, or 2MB L2 cache built in to the Pentium Pro, Pentium II/III, Xeon, or AMD Athlon CPU packages. The external L2 cache in those processors contains an additional 15.5 (256KB), 31 (512KB), 62 million (1MB), or 124 million (2MB) transistors in separate chips!
Note in Table 3.4 that the Athlon includes either 512KB of L2 cache via separate chips, running at either one-half, two-fifths, or one-third the core speed, or 256KB of on-die L2 running at full-core speed, depending on which version you have.
Processor Speed Ratings
A common misunderstanding about processors is their different speed ratings. This section covers processor speed in general, and then provides more specific information about Intel processors.
A computer system's clock speed is measured as a frequency, usually expressed as a number of cycles per second. A crystal oscillator controls clock speeds using a sliver of quartz sometimes contained in what looks like a small tin container. Newer systems include the oscillator circuitry in the motherboard chipset, so it might not be a visible separate component on newer boards. As voltage is applied to the quartz, it begins to vibrate (oscillate) at a harmonic rate dictated by the shape and size of the crystal (sliver). The oscillations emanate from the crystal in the form of a current that alternates at the harmonic rate of the crystal. This alternating current is the clock signal that forms the time base on which the computer operates. A typical computer system runs millions of these cycles per second, so speed is measured in megahertz. (One hertz is equal to one cycle per second.) An alternating current signal is like a sine wave, with the time between the peaks of each wave defining the frequency (see Figure 3.1).
Figure 3.1 Alternating current signal showing clock cycle timing.
NOTE
The hertz was named for the German physicist Heinrich Rudolf Hertz. In 1885, Hertz confirmed the electromagnetic theory, which states that light is a form of electromagnetic radiation and is propagated as waves.
A single cycle is the smallest element of time for the processor. Every action requires at least one cycle and usually multiple cycles. To transfer data to and from memory, for example, a modern processor such as the Pentium II needs a minimum of three cycles to set up the first memory transfer and then only a single cycle per transfer for the next three to six consecutive transfers. The extra cycles on the first transfer are normally called wait states. A wait state is a clock tick in which nothing happens. This ensures that the processor isn't getting ahead of the rest of the computer. Refrence http://www.informit.com/articles/article.aspx?p=130978&seqNum=4