Chapter 2 A+ Instructor Manual

Chapter 3

Microprocessors

Learning Objectives

In this lesson, you’ll identify various CPU types, upgrade a CPU, and install a CPU correctly. By the end of the lesson, you should be able to do the following:

· Identify core components of a CPU.

· Describe the relationships of CPUs and RAM.

· Explain the varieties of modern CPUs.

· Identify specialty CPUs.

· Install and upgrade CPUs.

Objectives for both the CompTIA A+ Essentials exam and the CompTIA A+ 220-602 exam are covered in this chapter.

Discussion Point

ESD

Recall, from the first lesson in Chapter 2, the issues concerned with electrostatic discharge (ESD) and the precautions that need to be taken when handling components. The CPU and RAM are both very susceptible to ESD damage.

Pre-test

1. What is a clock cycle? What does it mean if a CPU has a multiplier of 5×?

2. What does a process of 180 nm mean?

3. What does split voltage mean?

4. Describe a zero insertion force (ZIF) socket.

5. What is the function of thermal transfer heat compound?

Lecture Outline

Historical/Conceptual

I. Central Processing Unit (CPU) Core Components

A. External data bus

1. Uses binary (1 is on, and 0 is off) to communicate

2. Data lines on the bus can be switched (turned on or off) from inside or outside.

B. Registers

1. Worktables or temporary storage locations

2. CPU code book identifies CPU instructions that identify what to do with the data in the registers

C. Clock

1. Clock speed is the CPU’s maximum speed, not speed at which the CPU must run.

a) Used to synchronize eternal and external activity

b) One cycle per second = 1 hertz (Hz); 1 million cycles per second = 1 Megahertz (MHz)

c) Every command requires at least two clock cycles

2. Clock speed is the maximum clock cycles per second.

Discussion Point

Crystal is actually short for crystal oscillator. When a voltage is applied to a specially cut crystal (such as quartz), it will oscillate with surprising accuracy. This produces a pulse that is used to “clock” the CPU. Crystals can be cut to produce clocks at almost any speed. The speed of the crystal’s clock determines the speed at which the CPU will operate.

D. System crystal governs CPU running speed

1. Early motherboards had a fixed crystal speed.

2. Modern motherboards use jumpers to select crystal speed.

3. Crystal can clock a CPU with a rated speed higher than the crystal, but the CPU will operate at the slower speed of the crystal. In other words, a 1 GHz crystal can clock a 2-GHz CPU, but the CPU will operate only as fast as the crystal clock—1 GHz.

a) Underclocking means running a CPU slower than its rated clock speed. It does not take advantage of all the power of the CPU.

b) Overclocking means to run a CPU faster than its maximum clock speed. It can fry the CPU.

II. Memory

A. RAM stores programs and data while the CPU uses them.

B. Legacy memory storage options:

1. Paper cards

2. Magnetic cards

3. Magnetic linear tape

C. RAM: random access memory

1. Organized like a spreadsheet with each row holding 8 bits (or 1 byte)

2. Transfers and stores data to and from CPU in byte-sized chunks

3. Number of bytes of RAM varies from PC to PC, with today’s PCs holding hundreds of millions of bytes of RAM

4. RAM is volatile, clearing out when the PC loses power, in contrast to non-volatile or permanent storage devices such as hard drives

5. Address bus: Connects the CPU and RAM via a memory controller chip (MCC), which “grabs” the RAM that the CPU needs. An address bus is a set of wires that enables the CPU to address the RAM via the MCC.

a) The number of wires in the address bus determines the number of patterns or unique addresses that in turn determine the maximum RAM that a particular CPU can handle.

b) The 8088 CPU, the one used with the original IBM PC, contained 20 wires in its address bus, making it able to address a maximum of 1 MB of RAM.

c) Today’s CPUs have many more wires, allowing them to address several GB of RAM.

Discussion Point

Terminology

A bit of terminology to nibble and byte on:

Any individual 1 or 0 = a bit

4 bits = a nibble

8 bits = a byte

16 bits = a word

32 bits = a double word

64 bits = a paragraph or quad word

1 kilobyte = 1024 bytes (roughly but not exactly 1000 bytes)

1 megabyte (1000 KB) = 1,048,576 bytes (roughly but not exactly 1 million bytes)

1 gigabyte (1000 MB) = 1,073,741,824 bytes (roughly but not exactly 1 billion bytes)

1 terabyte (1000 GB) = 1,099,511,627,776 bytes (roughly but not exactly 1 trillion bytes)

Discussion Point

Binary

Given that the CPU, MCC, and RAM communicate in binary, now might be a good time to introduce binary counting.

First, review the value of a decimal number such as 643.

Start with three columns

102 / 101 / 100
100 / 10 / 1
10 squared or 10 × 10 / Any number to the 1 power is itself / Any number to the 0 power is 1
6 / 4 / 3
6 × 100 = 600 / 4 × 10 = 40 / 3 × 1 = 3

600 + 40 + 3 = 643

Now do the same thing with a binary number such as 101. Instead of a base 10, use a base 2 (binary) numbering system.

22 / 21 / 20
4 / 2 / 1
2 squared or 2 × 2 / Any number to the 1 power is itself / Any number to the 0 power is 1
1 / 0 / 1
1 × 4 = 4 / 0 × 2 = 0 / 1 × 1 = 1

4 + 0 + 1 = 5

Let’s not limit the discussion to just three bits ,but let’s add additional bits.

Binary / Decimal / Binary / Decimal
00000001 / 1 / 00000101 / 5
00000010 / 2 / 00000110 / 6
00000011 / 3 / 00000111 / 7
00000100 / 4 / 00001000 / 8

III. Modern CPUs

A. Modern CPUs retain the core structure of Intel 8088, including registers, instruction sets, and arithmetic logic unit. While modern processors share fundamental technology introduced by Intel, many differences prevent you from moving a CPU from one system to another.

B. Manufacturers: Two major manufacturers create CPUs.

1. Intel: Intel has dominated the industry with its CPU and motherboard support chips. Modern Intel processors include Pentium, Core 2 Duo, Centrino, lower-end Celeron, and higher-end Xeon.

2. AMD: Advanced Micro Devices has kept competition in the CPU market. While Intel holds the most market share, AMD often provides quality CPUs at competitive prices. AMD and Intel processors were interchangeable until the Pentium II. Although they often look similar today, they are not compatible.

C. CPU Packages: A number of different packages have been used for microprocessors. Modern CPUs use a pin grid array (PGA) package.

1. Pin grid array (PGA), very popular since the mid-1980s, fell out of favor during the Pentium II years, but is now the dominant CPU package. It has a square shape with hundreds of tiny pins.

a) Originally PGA sockets required a special tool to remove the CPU, but Intel designed a new type of socket called the zero insertion force (ZIF) socket that opens and closes with an arm.

b) A number of varieties of PGA exist, but most techs just refer to them all as PGA.

D. The Pentium CPU: The Early Years

Discussion Point

Moore’s Law

In 1965, Intel cofounder Gordon Moore predicted that the number of transistors on a chip would double about every two years. Variations of this prediction are largely quoted as Moore’s Law. In effect, the result is that processing power in CPUs doubles every two years, while costs decrease. While it hasn’t proven out exactly, looking at the progress over the years, his prediction was pretty close.
While many techs take this for granted today, imagine if we had the same level of improvements in other technologies. For example, what if every two years cars doubled their miles-per-gallon capacity? Or if every two years we could harness twice as much power from the sun?

1. Among the improvements that processors went through are a larger external data bus, larger address bus and registers, and faster clock speeds.

2. Intel introduced the Pentium CPU in the early 1990s, and the first CPU contained all the core functions that define today’s modern CPUs. The original Pentium had 32-bit registers, ran at speeds up to 300 MHz, was able to run multiple programs at once, had access to super-fast cache RAM, and could process two or more lines of code at the same time.

3. Most of today’s operating systems are 32-bit.

a) A 32-bit operating system can address 4 GB of memory.

b) 32-bit registers track all running programs.

4. Pipelining

a) Pipelining refers to the series of steps the CPU needs to go through to process a command such as Fetch, Decode, Execute, Write.

b) While the original processors had one single pipeline, current CPUs have a second set of circuitry that allows it to process more than one command at the same time (called pipelines.)

Discussion Point

Cache

Cache is a separate storage area that is used for quick access. Consider an encyclopedia article that you’ve found at the library. It took you some time to research it, locate the encyclopedia, and then locate the article. You read it and then return the encyclopedia to the shelf. Thirty minutes later, you realize you need to look at the article again. You need to go back and find the encyclopedia and locate the article again.
Instead, what you could have done is make a photocopy of the article when you located it the first time. Later, when you need to reference it again, you could just look at the photocopy.
Cache works the same way. When data is read (and sometimes written), it’s placed in a cache, so if you need it again later, it’s already there.
Processor cache is close to the processor and much quicker than RAM.

5. RAM cache

a) Processors have a small internal cache referred to as L1, which runs at or close to the speed of the CPU.

b) Almost all processors also have a much larger external cache referred to as L2, which was originally separate from the CPU, on the motherboard. Many processors today have an L2 cache on the chip.

c) Some high-end CPUs also have an L3 cache.

d) Cache uses synchronous RAM (SRAM), which is much quicker than dynamic RAM. (DRAM)

6. Clock speeds and multipliers

a) In early computers, the CPU ran at the same speed as the motherboard. Designers discovered that the CPU could run faster than the rest of the chips on the motherboard.

b) A clock-multiplying CPU uses a cache to run the CPU at a higher internal speed than the slower external operations (address bus, external data bus).

c) Clock multipliers range from ×2 up to almost ×30 and do not have to be whole numbers. It’s possible to have a multiple such as ×23.5.

d) Technicians had to set jumpers on older motherboards to configure the multiplier. Today, the motherboard is automatically configured through a function called CPUID.

7. CPU voltages

a) The more transistors a CPU has, the more heat it generates. Originally CPUs used 5 V. If you lower the voltage, you lower the heat.

b) Different CPUs use different voltages, making it difficult for motherboard manufacturers who had to use multiple voltage regulator modules (VRMs) and jumpers for the correct CPU voltage. If the correct voltage was not set for the CPU, it could destroy the CPU.

c) Modern motherboards can automatically determine the CPU voltage needs and switch the voltage accordingly.

8. Original Pentium: The basis of a whole generation of today’s chips

a) Specs: Internal speed of 50–66 MHz, external speed of 60–200 MHz, multiplier of 1× to 3×, L1 cache size of 16 KB, PGA package in Socket 4 or Socket 5.

b) AMD made a competing product called AMD K5.

E. Pentium Pro or P6

1. Specs: External speed of 60–66 MHz, internal speed of 166–200 MHz, multiple of 2.5× to 3×, L1 of 16 KB, L2 up to 1 MB, distinctive rectangular shape PGA package on a Socket 8 with 387 pins.

2. Sometimes referred to as the “Father of the Modern CPU.” It introduced important features that have been used on all other newer microprocessors.

a) Superscalar Execution (also known as quad pipelining on the P6). Gave it the ability to run more than one process in any given clock cycle. P6 could handle four separate pipelines.

b) Out of Order Processing/Speculative Execution. Improved branch prediction to a better than 90% success rate.

c). On-Chip L2 Cache. Major change was adding an on-chip L2 cache while retaining the L1 cache. The on-chip cache, while contained in the same housing, was not part of the CPU itself. Electronically, the CPU and the L2 cache were separate.

Discussion Point

Frontside Bus/Backside Bus

With the advent of the Pentium Pro, terminology changed a bit. From here on, the address bus and external data bus between the CPU, MCC, and RAM is called the frontside bus. The connection between the CPU and the L2 cache is called the backside bus.

F. Later Pentium-class CPUs

1. Specs: External speed of 66–75 MHz, internal speed of 166–200 MHz, multiplier of 2.5× to 4.5×, L1 of 32 KB, PGA package on a Socket 7.

2. Offer three groups of improvements

a) Multimedia extensions (MMX): Designed for graphics-intensive applications such as games.

c) Increased Clocks and Multipliers: Used up to 4.5× multiplier, as contrasted with the maximum 2.5× multiplier of early Pentiums.

G. Pentium II