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Chapter 4The Central Processing Unit and Memory

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Understanding Integrated Circuits

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Integrated Circuits

Integrated circuits are made up of semiconductor devices that act as electronic switches in digital circuits.

A semiconductor is capable of either conducting electricity or preventing its flow, depending on whether it is charged.

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Integrated Circuits (continued)

Integrated circuit (IC) chips are mass produced using a photolithographic process similar to contact printing.

An IC contains electrical components, such as transistors and resistors, and the electrically conductive pathways that connect them.

A typical microcomputer contains a motherboard on which is mounted a processor chip, a bank of memory chips, and various controller chips.

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The Motherboard

The motherboard provides electrical pathways among the chips.

Chips are designed to perform functions:· Processor Chips - often referred to as the central processing

unit (CPU), contains all the components necessary for computer processing.

· Memory Chips - contain thousands of millions of transistors for the storage of bit values.

· Special-Purpose Chips - some control video, sound, input devices, or storage devices.

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Motherboard Diagram

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The Central Processing Unit

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The Central Processing Unit

The “brains” of a computer system is the central processing unit (CPU).

The CPU:· Receives input· Interprets instructions provided by

programs· Processes data· Directs other components of the

system to act· Controls output

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The CPU Elements

Control Unit - coordinates the flow of data and instructions.

Arithmetic/Logic Unit - performs calculations and comparisons of data.

Registers - hold program instructions, data values, and memory locations as the processor executes a program.

Buses - carry bits between a CPU’s components and outside devices.

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Clock

The clock is part of the control unit. It provides a fixed stream of quartz-crystal-generated electrical pulses that the CPU and other components use for synchronization.

A clock circuit provides electrical pulses that the CPU and other components use for synchronization. Clock rates are usually quoted in millions of cycles (pulses) per second, or MHz (megahertz).

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Main Memory

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Main Memory (Primary Storage)

Accepts and holds program instructions and data. Acts as the CPU’s source for data and instructions,

and as a destination for operation results. Holds the final processed information until it can be

sent to the desired output or storage devices, such as a printer or disk drive.

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Storage Location and Capacities

Program instructions and data reside in individual memory locations, known as by their addresses.

Memory capacities are measured in bytes, kilobytes, megabytes, gigabytes and even terabytes.

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Random Access Memory (RAM)

Main memory is often referred to as random access memory (RAM).

Random access memory means that the computer can go directly to the instructions and data it wants using the memory address, rather than searching one location after another.

RAM is temporary, volatile memory.

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Read-Only Memory (ROM)

Read-only memory (ROM) is permanently stored, nonvolatile memory. Programs supplied on ROM chips are usually referred to as firmware.

Programmable read-only memory (PROM) allows users to write their own program on ROM memory chips.

Erasable programmable read-only memory (EPROM) chips can be erased and rewritten with new information.

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The Computer in Action

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The Machine Cycle

When a CPU executes a program, it reads each instruction, interprets it, executes it and stores the results to complete the operation.

This process of executing a single instruction is often referred to as the fetch, decode, execute and store cycle, or the machine cycle.

These four steps are broken down into two phases, the instruction cycle and the execution cycle.

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The Machine Cycle (continued)

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Advances in Microprocessors

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Technological Advances

Parallel Pipelining - increases performance by allowing execution of one instruction while another instruction is fetched.

Superscalar Architecture - designed to execute multiple instructions per clock cycle.

Branch Prediction - provides a sort of intelligence to the processor that can predict with a certain percentage of accuracy which way a program will branch.

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Technological Advances (continued)

CISC (complex instruction set computing). CISC chips contain a large set of instructions, each of which may take considerable decoding before it can be executed.

RISC (reduced instruction set computing). RISC chips provide fewer built-in instructions, and are generally faster than CISC chips because each instruction requires less decoding prior to its execution.

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Multiprocessor Systems

Originally designed for to accomplish high-end engineering/graphics tasks, multiprocessor systems are now used by most companies who need to process huge amounts of operational data very quickly.

Asymmetric multiprocessing systems are made up of processors that are each designed to handle a particular task.

Symmetric multiprocessing systems are made up of processors that can handle any task.

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Massively Parallel Processing

Massively parallel processing (MPP) systems are computers that are made up of hundreds, even thousands, of individual processors working together.

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The Development of Intel Processors

In 1981, IBM and Microsoft began co-marketing the operating system known as DOS (Disk Operating System) for use on the IBM PC.

The Intel 8088 microprocessor operated at 4.77MHz, could access up to 1MB of RAM and had an 8-bit data bus.

The Intel 80286 operated at 8-12MHz, could access up to 16MB of RAM and had a 16-bit data bus.

The Intel 80386 operated at 16-33MHz, and could have accessed up to 4 GB of RAM if all of the bits in its 32-bit address register had been used.

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The Development of Intel Processors (continued)

The 80486 has clock speeds of 25-100MHz, and is still capable of accessing up to 4GB of RAM. It also incorporates a built-in math coprocessor and 8KB of very fast memory cache.

The Pentium processors has speeds of 60-100MHz, has a 64-bit data bus and is capable of executing two instructions at once.

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Other Advanced Processors

DEC Alpha Chip - has a 64-bit register, data bus and address bus. The current Alpha processors run at 200 MHz and feature a peak throughput of 400 MIPS.

Motorola/IBM/Apple PowerPC 601 - are designed to power portable and desktop systems and provide the type of processing associated with graphic workstations. IBM systems will be able to run Macintosh software and Macintosh systems will be able to run IBM RS/6000 software.

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Other Advanced Processors (continued)

Silicon Graphics R4000 Series Processors - one major advantage of the R4000 is that it runs the Microsoft Windows NT operating system, which automatically guarantees they will run the applications already designed for this environment. The latest chip in this family is the R4400, which has a 75 MHz clock rate and is made up of 2.2 million transistors.

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Sun Microsystems SPARC Processors - Sun Microsystems and Texas Instruments have teamed up to create the MicroSPARC and SuperSPARC, 32-bit processors that run in the 40 MHz and 50 MHz, and run under UNIX. Future versions are scheduled to have 64-bit registers, data buses and address buses.

Other Advanced Processors (continued)

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Processors of the Future

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Future Processors

A new technique will use layers of transistors on a chip, rather than a single layer.

These new “super microprocessors” will include multiple processing units and replace the need to run multiple processors in parallel.