Pentium Class

Through the 80486, Intel had used numbers to identify its CPUs, but Intel found that its competitors used the same numbers for their compatible CPUs, and Intel could not legally trademark a number to prevent this practice. With the CPU that would have been known as the 80586, then, Intel changed to the name Pentium.

The Pentium CPU continued the evolution of the x86 line, with speed improvements and additional features, some of which were added late in the Pentium's lifetime. The multimedia extension (MMX) feature, for instance, appears only on late models of the Pentium CPU. The Pentium CPU is often touted as being 64-bit, but this refers to the number of bits it can transfer to and from memory in one operation, not to the size of its internal memory registers or the number of bits it uses to specify what memory address to fetch. The Pentium increased the

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size of the on-board cache relative to the 80486, and no Intel Pentium CPUs lacked an FPU. Intel introduced a new socket design for the Pentium, and that design went through a few minor revisions before settling on the popular Socket 7 layout (see Figure 1.2).

Figure 1.2

A Socket 7 CPU has more pins than a 486 CPU, and is physically larger as well.

Figure 1.2

A Socket 7 CPU has more pins than a 486 CPU, and is physically larger as well.

Prior to the Pentium, Intel's competitors had used CPU designs that were nearly identical to those from Intel, used under license. With the Pentium, Intel's main competitors (AMD, Cyrix, and NexGen early in the Pentium life cycle, with IDT added later) began using unique re-implementations of the x86 design. Some of these designs were radically different from the Pentium's design. For instance, the AMD K5 and NexGen Nx586 CPUs were the first to use a RISC core surrounded by logic to process complex x86 instructions through multiple RISC instructions. These unique designs make it difficult to compare the relative speeds of Pentium-class CPUs with those of different manufacturers' CPUs; the CPU clock speed alone is inadequate for comparisons. Some manufacturers used a P-rating or PR-rating to express their CPU's speed relative to a Pentium. For instance, the Cyrix 6x86 P-166 could be expected to run at the speed of a Pentium clocked at 166MHz—or so Cyrix claimed. In practice, speed varies from one application to another. P-ratings have largely fallen by the wayside, although Cyrix CPUs are still labeled with P-ratings.

To sum up, Pentium-class CPUs include

• Intel Pentium The "standard" for this class.

• Intel Pentium MMX Available in faster clock speeds and with the addition of MMX instructions.

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• NexGen Nx586 The NexGen Nx586 was the first Pentium clone chip. It was unusual among Pentium clones for several reasons, including the fact that it used its own socket design and, therefore, required its own motherboard. The early versions of the CPU also lacked an FPU. NexGen was subsequently bought by AMD.

• Cyrix 6x86 Cyrix named this CPU to suggest better-than-Pentium performance, and in integer arithmetic (the sort used by most programs), the 6x86 does outperform a Pentium at the same clock rate. This difference isn't great enough to make the 6x86 a competitor to the Pentium Pro or later Pentium versions, however. Cyrix did not have a manufacturing facility, and so the companies that manufactured the CPUs (mainly IBM) also sold them under their own names. Cyrix was bought by VIA in late 1999.

• Cyrix MediaGX The MediaGX was a variant of the 6x86 that incorporated many multimedia features into the CPU and motherboard chipset, rather than using add-on cards. MediaGX chips tend to appear in certain low-end motherboards from their day (mostly 1998). Although Linux can run on the MediaGX, the kernel doesn't support the advanced multimedia features of the chip, so you might have difficulty using these features of the computer. You might need to add a conventional video or sound card to use X or sound on Linux on a MediaGX computer, for instance.

• AMD K5 AMD's Pentium competitor was late and, in its first pressings, slightly slower than a Pentium at the same speed. Later versions of the K5 brought it into approximate speed parity with the Pentium at the same clock speed, but by that time AMD had introduced the K6, which quickly overshadowed the K5.

• IDT WinChip The IDT WinChip appeared very late in the Pentium life cycle and was never very popular. IDT announced in late 1999 that it was selling its WinChip design to VIA.

All of these CPUs are compatible with Linux. For best performance, you might want to recompile your kernel and select the appropriate CPU in the kernel configuration options (see Figure 1.3).

In 2000, Pentium-class systems are still adequate for running Linux, although older Pentium systems can be quite sluggish and even fast Pentium systems can be inadequate for tasks that are particularly demanding of the CPU, such as scientific simulations. No Linux distributions yet include optimizations that prevent them from running on Pentiums.

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Figure 1.3

The Linux kernel configuration provides options to help you optimize your kernel for the CPU in your computer.

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Figure 1.3

The Linux kernel configuration provides options to help you optimize your kernel for the CPU in your computer.

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