Chapter 9: A Closer Topics Discussed Look at System Hardwaredreed/CS10001/Archives/Fall_2007/Notes/ch_9_pl… · the electrical flow of digital information. ... Holds all the data

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Chapter 9: A Closer Look at System Hardware 1

Chapter 9: A Closer Look at System

Hardware

CS10001 – Computer Literacy


Topics Discussed

Digital Data and Switches Manual Electrical

Digital Data Representation Decimal to Binary (Numbers) Characters and Symbols Other (Negative, Fractional, Hexadecimal)

CPU Digital Processing Machine Cycle In-Depth Machine Cycle Stages


Digital Data

Recall that bits are the alphabet of the binary language. They represent the status of “off” (0) or “on” (1).

Bits may be thought of as language devices that control the states of “off” or “on”. They are considered to be binary switches.


Digital Data

Electrical switches are devices inside the computer with the capability of representing the states of the binary language, 0 or 1.

So, computers are nothing more than big devices of electrical switches? How is that accomplished?

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Examples of Switches

Vacuum tubes allowed or blocked the flow of electrical current in early computers (1940s). Big Bulky Unreliable Unsafe

Vacuum tube



Transistors incorporated silicon semiconductors to allow or block the electrical flow of digital information. Smaller Cheaper Cooler Still big Transistors



Integrated circuits are microprocessors, or chips, embedded with a CPU. Contains millions of transistors in a very small space (1970s). Smallest Cheapest Fastest

Integrated circuit


Digital Data Representation

Recall that the binary number system is the language of computers. It is used by the computer to represent all data, instructions and programs.

Because it is a “number system”, it is an organized plan for number representation.

It consists of two digits: “0” and “1”.

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Converting Decimal Numbers to Binary

Technique #1 1. Find the largest base 2 number in the

decimal number.

2. Set that placeholder to “on” or 1.

3. Subtract that number from the original decimal number to get a remainder.

4. Perform steps 1-3 on the remainder until the binary number is determined.


Converting Decimal Numbers to Binary

Technique #2 1. Divide the decimal number by 2.

2. Calculate the remainder as “0” or “1”.

3. Perform steps 1-2 until all divisions are exhausted.

4. The binary number is determined by writing the remainder digits from the bottom to the top.


Storing Letters and Symbols in Binary

EBCDIC (Extended Binary Coded Decimal Interchange Code) Provided the first means of consistent

representation of letters and characters that the computer could understand.

Used in early mainframes.



ASCII (American Standard Code for Information Interchange) Used to represent letters or characters

in one byte.

Included 26 uppercase letters and 26 lowercase letters, punctuation symbols and special characters.

Allowed for 28 or 256 combinations.

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Unicode Expanded ASCII and allowed a

representation of all characters and all symbols for all languages (historic and modern).

Utilized 16 bits for the representation of one byte.

Allowed for 216 or approximately 65,000 combinations.


Other Binary Representations

Negative numbers Uses a sign bit CPU notified by program

Fractional numbers Utilize a 32-bit system Representations standardized by IEEE

(Institute of Electrical and Electronics Engineers)


Other Binary Representations

Hexadecimal numbers Uses an alphabet of 16 digits, 0-9 and

A-F. Easier representations for humans

because binary strings are too long and cumbersome.

Where else was the hexadecimal number system discussed? This will likely be seen on our class project.


The CPU and Digital Processing

Recall that the CPU is: The “brains” of the computer. Fits on a microprocessor chip. Is located on the motherboard with

memory. Executes all the instructions (user-

defined or operating system). Is part of the computer system’s

platform.

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The CPU and Digital Processing

How are CPUs different? By processing power (number of

transistors). By clock speed (its work pace). By amount of immediate access

memory (cache). By hyperthreading (processing two

separate instruction sets--one before the other finishes or both simultaneously).


In Depth: The CPU Machine Cycle

Recall that the machine cycle is the pace at which instructions and programs are processed by the CPU.

Measured in Hz (Hertz) and clock speed, as determined by the system clock.

It has four steps: fetch, decode, execute and store.



The system clock is built into the motherboard and controls the stages of the machine cycle.

Its clock cycle beats steadily and sets the processing pace.

The clock speed is the pace at which machine cycles are occurring.



The CPU’s control unit manages the switches inside the CPU so that it can remember the proper stage of the machine cycle (preprogrammed).

With each beat of the system clock, switches are set for that stage.

The work associated with that stage is performed.

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In Depth: Machine Cycle Stages

Fetch Stage Gathers the necessary binary code for

the instruction or program from RAM. Moves the instruction from RAM to the

CPU registers which are special storage areas on the CPU.

The instruction remains in the registers until executed.



Fetch Stage – cont’d: Using cache memory Level 1 is on the CPU.

Level 2 is on the CPU but farther away.



Decode Stage Translates the instruction into

something the CPU understands.

Uses specific instruction sets for the translation.

Signals the registers (via the control unit) about which data to send to the ALU.



Execute Stage Data is sent to the ALU from the

registers, based on word size.

The ALU performs the calculations on the data. Arithmetic: Add, Subtract, Multiply, Divide

Comparison: <, >, =, not equal

Logical: AND, OR, NOT

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Store Stage Result from the ALU is stored in the

registers. Register for storage is noted in the

instruction.

The cycle begins again with the next instruction to be processed.


Other Topics Discussed

Other RAM Dynamic RAM Static RAM

The Bus Local bus Expansion bus

Making Computers Faster Pipelining New instruction sets Multiple processing Parallel processing


RAM: More Temporary Storage

Recall that RAM: Is located on the motherboard in

memory modules (memory cards). Holds all the data and instructions

needed by the CPU and OS. Has an access time measured in

nanoseconds. Measured in MB or GB.



DRAM (Dynamic RAM) Cheap and basic Access time = 60ns Uses transistors, capacitors and

refresh signals for individual bits.

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DRAM (Dynamic RAM) – cont’d.

Hierarchy

SDRAM (synchronous DRAM)

DDR SDRAM (double data rate SDRAM)

DDR2 SDRAM



SRAM (Static RAM) Faster than DRAM

More expensive than DRAM

Uses more transistors for bits, but no capacitors or refresh rates

Commonly used for the CPU cache



What else about RAM memory modules? DIMMs (dual inline memory modules) Pentium processors, 64-bit bus

SIMMs (single inline memory modules) Pre-Pentium processors, 64-bit bus was

emulated in matched 32-bit buses


Bus: CPU Data Highway

A bus is an electrical wire located within the system circuitry. Considered to be a data “highway”

This highway is traveled by data (bits) and links the various computer components.

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Two bus types: Local bus On the motherboard

CPU to main memory data transfer

Expansion bus From expansion cards to motherboard

Seen in video and audio



Bus Speed – More Data at a Time? Bus clock speed is the data transfer

rate from one location to another (MHz).

Bus width determines the number of bits traveling at a time (wider is better).

Bus clock speed X bus width = Data transfer rate of the bus.



Bus Speed – More Speed with the Data? The bus width determines the word

size to the CPU, or the number of bits manipulated at a time.

What happens if the CPU can manipulate more bits than the bus delivers?

Bus width limitations affect the CPU’s processing performance.



Expansion buses ISA and EISA connected mouse,

modem, sound card. PCI direct CPU connection for

networks and sound. AGP for graphics transfer so the PCI is

not clogged.

See page 424 for architecture details.

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Making Faster Computers

Advanced CPU Designs

Pipelining

New instruction sets

Multiple processing

Parallel processing



Pipelining is a technique used to boost CPU performance. CPU works on more than one

instruction at a time.

More instructions processed in a clock cycle.

More efficient CPU processing.



Nonpipeling vs. Pipelining

Fetch Decode Execute Store

Fetch Decode Store

Nonpipelined CPU

Fetch Decode Store

Fetch Decode Store

Fetch Decode Store

Fetch Decode Store

Instruction 1

Instruction 1

Instruction 2

Instruction 2

Instruction 3

Instruction 4

Pipelined CPU

Execute

Execute

Execute

Execute

Execute



New instruction sets The basic instruction set is the

collection of commands executable by a specific CPU.

New commands to accommodate video, audio and image processing are inserted in the basic instruction set.

New instruction sets are the result.

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Multiple processing Dual-processor Two physical CPU chips installed Used on high-end servers or mainframes

Dual-core processing Uses hyperthreading Runs multiple stages of the machine cycle

simultaneously “Appears” as if two CPU chips are present



Parallel processing Designed to solve one complex

problem. Large network of computers. Each computer works on part of the

problem. Tasks are completed simultaneously.

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Chapter 9: A Closer Topics Discussed Look at System Hardwaredreed/CS10001/Archives/Fall_2007/Notes/ch_9_pl… · the electrical flow of digital information. ... Holds all the data