Looking at Microprocessors






Looking at Microprocessors

Everything that a computer can do for you — that is, all its magic — is performed by its microprocessor. The microprocessor performs all the arithmetic, logic, and computing actions of a PC. You may see your PC as a word processor, a computer game, a World Wide Web browser, an e-mail tool, or any of the other tasks that you perform on your PC. In fact, each of these tasks is software that is made up of thousands of instructions that the CPU executes one at a time to create the actions that you see and use. The processor, which is short for both microprocessor and central processing unit (CPU), is the electronic circuitry that uses digital logic to perform the instructions of your software.

Technically speaking, a microprocessor is an integrated circuit that contains millions of transistors that are interconnected by small aluminum wires. The microprocessor’s processing capabilities control and direct the activities of the PC by interacting with the other electronic components on the motherboard, such as the main memory, bus structures, cache memory, and device interfaces.

 Remember  You need to know about microprocessors in detail for the exam. This includes nitpicky stuff such as clock speeds, bus widths, features that are included or supported, mountings, packaging, manufacturer, and evolution. The subject of processors is an area where test writers can’t resist getting specific. In many areas of the test, a sound, general knowledge of a subject can be enough to get you through, but not here. You need to know this stuff in detail.

On the CPU bus

The bus, as it relates to the pathways on the computer and in the processor, carries the various signals, addresses, and data that move about the PC between its components. The bus is a group of electronic transmission lines that interconnect the components of the CPU, motherboard, and expansion cards. Bus structures have different sizes, ranging from 16 to 64 bits on modern microprocessors, which determine the amount of data that can be transmitted. Just as an 8-lane highway carries more traffic than a 2-lane road, a 64-bit bus carries more data than a 16-bit bus.

A PC has several distinct bus structures; the most important are as follows:

  • Data bus: Carries data to and from the CPU, main memory, and peripheral devices. The width (in bits) determines the amount of data that can be transmitted at a time.

  • Address bus: Carries addresses of data and instructions between memory and the CPU. The width (in bits) determines the size of the address (represented as a binary number) that can be passed over the address bus.

  • Control bus: Carries control information, such as the status of the devices, between the CPU and other devices. The information that is passed over the control bus provides data that indicates that data is ready to be read or a device is waiting to use the bus, and indicates the type of operation that a device is requesting (read, write, or interrupt).

Chapter 5 is dedicated to the bus structures of a PC.

CPU packaging

The microprocessor and its associated electronic circuits are packaged in a protective outer packaging. When you look at a processor, you see the packaging, not the microprocessor itself. Typically, the processor’s packaging is ceramic or plastic.

The outer covering of the processor protects its core (also called the die), which contains the microchip and the wiring that connects the chip to the processor’s mounting pins. A variety of packaging types have been used on processors. You should know the following types for the A+ Hardware Technology exam:

  • Pin Grid Array (PGA): Common among early processors, the mounting pins are located on the bottom of the chip in concentric squares. Figure contrasts this package to the Single Edge Connector (SEC) package. The earliest chips were packaged in the Ceramic PGA (CPGA). Later chips, including some current ones, use the Plastic PGA (PPGA). The early Pentium chips used a variation that staggered the pin pattern (to cram more pins onto the package) and surprisingly was called the Staggered PGA (SPGA). The Pentium III features a variation of the PGA package with its Slot 370–like Flip Chip–Pin Graphics Assembly (FC-PGA).

    Click To expand
    Figure: A comparison of the Pin Grid Array (PGA) and the Single Edge Connector (SEC) processor packaging styles.

  • Plastic Ball Grid Array (PBGA): The primary difference between this packaging technology and the PGA is that the PBGA doesn’t have mounting pins projecting from the bottom of the chip; this eliminates the threat of bent pins on the bottom of the processor. Otherwise, these package styles look similar.

  • Single Edge Connector (SEC): You may find a few variations on the name of this packaging technology, including the Single Edge Contact Cartridge (SECC) and others. They all boil down to a packaging style that is mounted perpendicular to the motherboard into a single slot, much like expansion cards and memory modules. The Pentium II was the first processor to sport this new packaging style.

Keeping the processor cool

Before the Intel 486, microprocessors were cooled primarily by the airflow inside the case that was created by a system fan in the power supply. This process was called radiant cooling. Any heat that was radiated by the processor was cooled by air being sucked by the fan into the system case. Beginning with the 486, processors are cooled with a processor cooling fan or a heatsink or both, attached directly to the surface of the processor. In addition, the system fan was reversed to extract the heated air from inside the computer case and force it out.

With the Pentium processors came heat and cooling problems for the PC. The Pentium chip runs much hotter than earlier CPUs and requires special heat dissipation and cooling. You need to know a few things about the heat problems and cooling requirements of the Pentium chips for the exam.

The Pentium I processor operates at 85 degrees Celsius (about 185 degrees Fahrenheit). The Pentium III processor operates at 100 degrees Celsius (about 212 degrees Fahrenheit, the boiling point of water). The PC’s cooling system is designed to keep the processor operating near its optimal temperature. Therefore, you need to keep the PC’s case closed to ensure that its cooling system is operating efficiently and as designed. The form factor for the case, motherboard, and power supply that supports a particular processor is designed to provide cooling to keep the processor at or near its optimal operating temperature. At temperatures above its normal operating temperature, a processor begins to perform poorly, shuts down, or becomes permanently damaged. Heatsinks and fans are designed to draw the heat up and out of the processor’s packaging and carry the heat away on the tines of the heatsink by the airflow of the fan.

On Pentium and Pentium Pro processors, heatsinks and fans are clipped directly on the processor and attached with a dielectric gel, which is also called thermal grease. Later processor models, such as the Celeron, the Pentium II, and the Pentium III (all of which have SEC packaging), have mounting points to attach fans and heatsinks directly to the processor.

In addition to the airflow system of the PC, the Pentium processor also uses special motherboard configurations to help cool it. This may include a fan or a heatsink (or both), mounted directly on top of the processor. The fan sucks the heat away from the chip and up into the PC’s airflow. A heatsink is a device that looks something like a bed of nails that wicks the heat into its tines, where the airflow removes it. If a processor has both a fan and a heatsink, the fan sits on top of the heatsink.

Thermal grease (also known as heatsink jelly, heatsink compound, thermal gunk, thermal compound, or thermal goo) improves the heat conductivity between the processor and its heatsink. The grease eliminates any gaps between the two devices, working like a denture adhesive, allowing the CPU’s heat to transfer to the heatsink more efficiently.

Feeding power to the processor

Most motherboards include a mounting for a voltage regulator module (VRM), which is a device that regulates the voltage that is fed to the processor. The mounting serves the following purposes:

  • To protect the processor from spikes or other electrical events coming from the power supply

  • To ensure that a steady flow of power is fed to the processor

Typically, the VRM is located very near the processor mounting slot or socket.

Comparing sockets and slots

Two general types of mountings are used to mount processors to the motherboard: sockets and slots. Most processors are available in only one mounting style, disregarding ceramic versus plastic. Other processors, such as the Celeron, are available in either a PGA-type or an SEC-type package.

Socket to it

 Remember  A variety of socket types have been used for PC microprocessors. For the exam, pay close attention to those used for Pentium-class processors. You should expect to encounter the following socket types on the A+ Hardware Technology exam:

  • Socket 4: Mounts the 273-pin PGA package of the Pentium 60 and Pentium 66 processors.

  • Socket 5: Mounts the 320-pin Staggered Pin Grid Array (SPGA) of early 3V Pentium processors.

  • Socket 7: A socket type, still in use, that mounts the 321-pin SPGA of the later-release Pentium processors and the chips of AMD, Cyrix, and IDT.

  • Super 7: An extension of the Socket 7 design that is used for the AMD K6 processors.

  • Socket 8: A 387-pin SPGA zero-insertion-force (ZIF) socket for the Pentium Pro processor.

  • Socket 370: Designed for the Celeron processor in Plastic Pin Grid Array (PPGA) packaging, but used for several later processors. Its name comes from the number of pins that it supports. See Figure.

    Click To expand
    Figure: A Socket 370 mounting.

  • Socket 423 P4: Along with the Socket 478 Pentium 4 mounting, this is one of two sockets used for the Pentium 4 processor. According to Intel, the Socket 423 P4 mounting is optimized for Windows XP.

  • Socket 478 Pentium 4: Along with the Socket 423 P4, the Socket 478 Pentium 4 mounting (see Figure) is one of the two types of sockets used for Pentium 4 processors.

    Click To expand
    Figure: A Socket 478 Pentium 4 mounting.

  • Socket A/Socket 462: This is an American Micro Devices (AMD) 462-pin socket that is replacing the Slot A mounting for the newer Athlon and Duron processors.

Slot types

 Remember  Slot type connections use a single slot mounting on the motherboard that mounts the processor in the same manner that is used for memory modules or expansion cards. The packaging technologies that mount in slot connectors include Single Edge Processor Package (SEPP), Single Edge Connector Cartridge (SECC), and similar types that involve the words single edge.

The following types of slot mountings are used to attach microprocessors to motherboards:

  • Slot 1: Technically called the SC-242 (Slot Connector — 242 pins) connector, this is a proprietary Intel connector that is used for Celeron, Pentium II, and Pentium III processors.

  • Slot 2: Technically the SC-330 connector, the Slot 2 connector is an Intel mounting for its Pentium II Xeon and Pentium III Xeon chips. This slot style enhances the ability of multiple processors that are installed in the same PC to work together.

  • Slot A: AMD Athlon processors use this slot style, which is physically the same as a Slot 1 connector. However, the Slot A type uses different pin assignments, making it unusable by Intel processors.

  • Slot M: This type is designed to hold the 64-bit Intel Itanium processor.

Intel processors

Most of the PCs that you work on as PC repair technician have processors from Intel Corporation, and because Intel is one of the companies that helped develop the A+ exams, you can expect most of the processor questions to relate to Intel processors.

 Time Shaver  For the exam, about the only Intel-specific thing that you need to remember are the numbering and naming schemes that Intel uses for its CPUs, and how these schemes contrast with the processors of other manufacturers. You won’t be asked to identify the manufacturer of a CPU, but knowing Intel’s evolution may help you to identify incorrect answers of a question.

 Remember  Based on the A+ Hardware Technology exam objectives, you need to know the type of mounting, voltage, clock speed, and bus width for each of the popular (meaning Intel) microprocessors. Figure includes information for the CPUs that you need to know for the test. The order of the processors in the table is important because it indicates their evolution, although the later processors do overlap a bit.

Figure: Intel Microprocessors

CPU

Core Speed (MHz)

Voltage (volts)

L1 Cache (KB)

L2 Cache (KB)

Mounting

Pentium P5

60–66

5

8 WT/8 WB

-

Socket 5

Pentium P5

75–333

3.3

8 WT/8 WB

-

Socket 7

Pentium Pro

166–200

3.3

16

512

Socket 8

Pentium II

233–450

2.8

16 WT/16 WB

512

Slot 1

Pentium II Xeon

400–450

2

16 WT/16 WB

512/1024/2048

Slot 1

Celeron

266–300

2

-

-

Slot 1

Celeron

300–533

2

16 WT/16 WB

128

Slot 1/Socket 370

Celeron

533–700

1.7

16 WT/16 WB

128

Socket 478

Pentium III

450–1266

1.7–2

16 WT/16 WB

256/512

Slot 1/Socket 370

Pentium III Xeon

500–1000

2

16 WT/16 WB

256/512/1024/2048

Slot 1

Pentium 4

1300–2533

1.75

socket

256

Socket 478 P4

In Figure, the L1 (Level 1) cache is listed in the form of 8 WT/8 WB or 16 WT/16 WB in most places. This indicates that the processor has either 16 or 32K of L1 cache, but the 16 or 32K is divided into halves that perform either write-through or write-back caching operations. (See Chapter 3 for more information on caching.)

Brief descriptions of each of the processors that are included in Figure are as follows:

  • Pentium: This processor features 32-bit multitasking using RISC (Reduced Instruction Set Computer) design techniques and a superscalar architecture that executes two instructions in the same clock cycle. The Pentium expanded the internal bus to 64 bits and high-speed internal cache.

  • Pentium Pro: The Pentium Pro was developed as a network server processor. It was specially designed to support 32-bit network operating systems, such as Windows NT, and to be used in configurations of one, two, or four processors, with 1 megabyte of advanced Level 2 (L2) cache.

  • Pentium II: The Pentium II is the Pentium Pro processor with MMX technology added. The P-II, as it is commonly referred to, is excellent for multimedia work that requires support for full-motion video and 3D images.

  • Celeron: Developed for use in desktop and portable computers, the Celeron is a low-cost version of the Pentium II processor.

  • Pentium III: Although recently surpassed by the Pentium 4, the Pentium III has been the highest-powered processor in the Intel arsenal. It features 9.5 million transistors, a 32K L1 cache, 512K of L2 cache, and clock speeds of 450 MHz to 1 GHz.

  • Xeon: The Xeon processors, both Pentium II and Pentium III, are successors to the Pentium Pro processors. The Xeon is a network server processor that is capable of addressing and caching up to 64GB of memory with its 36-bit memory address bus. Xeon processors can be configured with four to eight CPUs in one server.

  • Pentium 4: Using the first totally new processor design since the Pentium Pro, the Pentium 4 (P4) processor has clock speeds that exceed 2 GHz, or about twice the speed of the Pentium III.

Caching in on Level 3

 Remember  The A+ Hardware Technology exam objectives include a reference to Level 3 (L3) cache. Don’t panic if this is a new term to you; it is to just about everyone as well.

When the processor manufacturers began including L2 cache on the processor package, any cache that was located on the motherboard — or outside the processor — was demoted to Level 3.

AMD processors

American Micro Devices (AMD) is the manufacturer of the K6, Athlon, and Duron processors, which compete with the Intel Pentium processors. Figure lists the common AMD processors.

Figure: AMD Microprocessors

CPU

Core Speed (MHz)

Voltage (volts)

L1 Cache (KB)

L2 Cache (KB)

Mounting

K6

166–266

3.3

32 WT/32 WB

256

Socket 7

K6

266–300

2.2

32 WT/32 WB

256

Socket 7

K6-2

266–550

2.2/2.3

32 WT/32 WB

256

Socket 7

Athlon

500–1800

1.75

64 WT/64 WB

512/256

Slot A/Socket A

Duron

600–1200

1.6

64 WT/64 WB

64

Socket A



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