PROCESSORS AND MODES

In 1978, the Intel 8086 processor was introduced. Recently, many of the processors on the market have been based on the characteristics of the 8086 processor. Several modes and advancements in early processors designed to maintain backward compatibility with the original 8086 processor are worth mentioning.

Real Mode

Provided by the 8086 (XT) processor, real-mode processing offers the processor access to the limited memory space or environment of 1MB (1024K of memory addresses). Real mode uses a 16-bit data path and has a direct access path to RAM.

Protected Mode

Introduced with the 80286 processor, protected mode allows the processor to access memory above 1MB (1024K) and up to 16MB. Protected mode allows programs to use a 32-bit data path.

Virtual Real (Protected) Mode

Introduced with the 80386 processor, virtual real (protected) mode allows multiple programs to run at the same time in their own protected separate memory addresses or Virtual Machines (VMs). If one of these programs or VMs fails, the other programs are not affected.

386DX

Made of CMOS material, the 386DX provides 32-bit processing power and can run in virtual real mode. A 386 operates at +5V, is capable of addressing up to 4GB of memory, and has an internal cache. The clock speeds for 386DX range from 16MHz to 33MHz.

386SX

Released in 1988, the 386SX is a scaled-down version of the 386DX. It has a smaller, 16-bit external bus and a 24-bit memory address bus that addresses 16MB of RAM. This makes the 386SX less expensive than the 386DX. It was available from 16MHz to 33MHz.

386SL

In 1990, the 386SL was introduced to meet the demand for a smaller processor with lower power consumption. This need came from the desire for laptop computing systems that required smaller components. The 386SL is basically the 386SX designed for laptops and their power management capabilities. The 386SL was offered with a 25MHz clock speed.

486DX

The 486DX featured 32-bit internal and external memory address buses. It offered internal Level 1 cache at 8K. This processor introduced burst mode memory and had a coprocessor or Floating-Point Unit (FPU) integrated into the CPU chip.

486SX

The 486SX is a scaled-down version of the 486DX processor. The math coprocessor was disabled by the manufacturer and sold as a lower-cost alternative to the DX model.

486DX2

The 486DX2 was designed to run at double the speed (with the exception of the external bus) of its predecessor, the 486DX. The 486DX2 processor operates at +3.3V.

AMD 5X86 (K5)

The AMD K5 was offered as a 75MHz to 133MHz processor, released by AMD. It was produced to be competitive with early Pentium CPUs. It offered 50, 60, and 66 bus speeds, and an internal (primary) cache of 24K. The AMD K5 uses Socket 7 technology. The K5 has a Level 1 cache of 24K.

CYRIX 5X86

A Socket 7-type CPU released to compete with early Pentiums.

The Early Pentiums (60MHz To 200MHz)

The first Pentium processor, which became known as the classic Pentium I, was offered in 1992, and it was backward compatible with previous Intel processors. The early Pentiums operated with a data bus of 64 bits, an address bus of 32 bits, and a 64-bit memory bus. It offered 16K of Level 1 cache. The Pentium I introduced the single-cycle instruction technology known as dual pipelining.

Pentium Pro

The Pentium Pro offered onboard Level 1 cache at 16K and Level 2 cache at 256K, 512K, or 1MB, which answered the need for large amounts of cached memory. It introduced the concept of quad pipelining and dynamic processing. The Pentium Pro worked well for a program-intensive workstation or server. Unfortunately, it did not handle 16-bit (DOS) application code well.

AMD K6

The K6 was developed as competition for the Pentium Pro. Speeds available were 166MHz, 200MHz, 233MHz, 266MHz, and a Super Socket 7 version designed to run at 100MHz motherboard bus speed and higher clock speeds. The AMD K6 has an internal cache size of 64K.

Cyrix 6X86MX

In order to compete with the Pentiums, AMD and Cyrix developed a Processor Rating (PR) system designed to match up equivalent competitor clock speeds. The Cyrix 6x86MX processors ranged from PR-166 to PR-366. The 6x86 had an external bus speed of 75MHz.

Celeron

Introduced as a lower-end Pentium II, the Intel Celeron processor came to the market to answer the need for less-expensive chips that could keep pace with the Pentiums. Depending on its version, the Celeron could be purchased in PII- or PIII-comparable speeds. Celeron packages came in PGA or FC-PGA format and required a 66MHz motherboard. The Celeron is compatible with Multimedia Extensions (MMX). It has a Level 1 cache of 32K.

In May of 2002, Intel introduced a new Celeron based on the same technologies used to produce the Willamette Pentium 4. This Socket 478 processor came in speeds of 1.7GHz and 1.8GHz. It offered 128k of L2 cache (as opposed to the Pentium 4’s 256K), ran at 1.75V, and had a 400MHz front side bus (100MHz quad pumped effective at 400MHz). In November of 2002, Intel would release a newer, updated Celeron model based on the Pentium 4 Northwood Core. It was offered as a 2.0GHz product (Socket 478) running at 1.5V, with 128k of L2 cache, and a 400MHz front side bus (100MHz quad pumped effective at 400MHz).

Xeon

The Xeon processor succeeded the Pentium Pro. It was meant to be a server computer processor, primarily because of its choices of Level 2 cache, which was available at 512K, 1MB, or 2MB. It was also noted for its ability to support up to eight processors in one computer and up to 64GB of memory.

Pentium II

The Pentium II processor is available in 233MHz, 266MHz, 300MHz, 333MHz, 350MHz, 400MHz, and 450MHz clock speeds. This processor is designed to take full advantage of MMX technology. MMX introduced new hardware technology processing that is integrated into the system for better calculation and acceleration of multimedia. The Pentium II provides a larger pipeline cache size than its predecessor, the Pentium I. It has a Level 1 cache of 32K and a Level 2 cache of 512K. The Pentium II uses Slot 1 technology. In Table 16.1, you can see a comparison of Pentium II processor speeds to their corresponding motherboard clock speeds.

Pentium III

Pentium III offers 32K of Level 1 cache and fully supports Level 2 cache at 512K. It is offered with clock speeds that range from 450MHz to 1.4GHz. It is available in a second-generation SEC package known as SECC2. Remember, the Pentium III utilizes both Slot 1 and Socket 370 technologies.

AMD Athlon and Duron

A processor available through AMD is the AMD 1GHz Athlon processor. It replaces the AMD K-6 series. It is available in both Slot A and Socket A formats, and boasts a 200MHz to 400MHz Alpha EV-6 bus.

The AMD Duron, released to the public in 2000, was meant to be the Celeron’s major competitor. The AMD Duron was developed for the mid-range workstation market. The Duron processor clock speeds range from 600MHz through 1.3GHz. The Duron used either Slot A or Socket A technology, and has the Level 2 cache internal to the processor (unlike the Athlon, which has the Level 2 cache external to the processor), and is rated at a motherboard speed of 100MHz.

Table 16.1: Pentium II Processor and Motherboard Speed Comparison

Pentium II Processor Speed	Motherboard
233MHz	66MHz
266MHz	66MHz
300MHz	66MHz
333MHz	66MHz
350MHz	100MHz
400MHz	100MHz
450MHz	100MHz

Athlon XP

The Athlon XP was introduced in November of 2001 by AMD as a follow-up to the very successful Athlon line of processors. Athlon XPs range in speed from 1.33GHz to 2.167GHz, but you won’t find them listed anywhere with those clock speeds. AMD decided, in an interesting public relations move, to rename the processors according to how they compared to previous Athlon processors. For example, an Athlon 1500+ (clocked at 1.3GHz) is comparable with the previous Athlon model clocked at 1.5GHz (had they gone over 1.4GHz with the classic Athlon). The difference in performance was attributed to “Quantispeed Architecture,” which (in simplified terms) means that the processor is handling more operations per clock cycle—not new technology, just a catchy new name.

The original XPs, based on the Palomino core, came clocked at 1.33GHz (XP 1500+) through 1.60GHz (XP 1900+). These processors were soon replaced with a processor revision dubbed the Thoroughbred, which reduced the core size utilizing the 0.13-micron process. The advantage to the revised line with the smaller core was that lower core voltages could be utilized for lower clocked processors. Voltage requirements scaled with processor speed, so a 1.47GHz (1700+) would only require 1.50V, while the higher-clocked processor at, say, 1.80GHz (2200+) required 1.65V. (Lower voltage consumption rates meant less heat, which made it more attractive to consumers at large.) Both Thoroughbred and Palomino Athlon XPs utilized a 266MHz front side bus (133MHz double data rate effective at 266MHz), with 256K of L2 cache. All of the processors in the Athlon XP line use Socket A technology, with DDR-SDRAM memory options in chipsets being the memory configuration of choice.

Only recently has the XP line of processors again been revised. The newly released Barton core boasts not only a larger L2 cache (512K), but also a faster front side bus, effectively at 333MHz. Bartons are currently being offered in variable speeds, all the way up to 2.167GHz (Athlon XP 3000+).

Pentium 4

Originally introduced July 2, 2001, the Pentium 4 ranges in speed from 1.3GHz to 3.06GHz. It is important to realize, however, that the Pentium 4 has undergone some serious changes throughout its life span.

When the Pentium 4 was introduced in mid-2001, it was available as a Socket 423 and (in later processor models) Socket 478 processor. Dubbed the Willamette, it came with a 400MHz (100MHz quad pumped effectively 400MHz) front side bus and 256K of L2 cache. In this form, it was available in speeds that ranged from 1.3GHz to 2.0GHz. These processors were only used with costly RDRAM (Rambus), and generally were regarded as “fast but too expensive.”

In early 2002, however, the current iteration of the Pentium 4 was introduced: the Northwood. The Northwood is based solely on Socket 478 technology, and out of the gate offered 512K L2 cache. The extra 256K of L2 cache offered a 10% performance increase for similarly clocked processors (as there was overlap of processor speeds between the Willamette and the Northwood). It is also important to note that the physical size of the silicon core had been reduced from 217mm² to 146mm². The decrease in core size also benefits the new Northwood in terms of voltage requirements, as the requirement dropped from 1.75V (for Willamette) to 1.5V. With these processors came the several different chipsets supporting several different memory types, from SDRAM, DDR SDRAM, and, of course, the original RDRAM.

The Northwood core, itself, has undergone changes since its inception. The 533MHz (133MHz quad pumped effective at 533MHz) front side bus versions of the processor were released in May of 2002. And only just recently, the 800MHz (200MHz quad pumped effective at 800MHz) front side bus version has been released.

The test is likely to present you with questions that test your knowledge of processor/motherboard compatibility and speed. For example, you should know that early Pentiums, such as the 75MHz Pentium, were designed to run at a 66MHz motherboard bus speed. The original Pentium through the Pentium II 333MHz processors were designed to run at 66MHz motherboard bus speed. The Pentium II 350MHz through the Pentium III series processors are intended to run at 100MHz motherboard bus speed.