CSCE 106Fundamentals of Computer Science

Assisting Slides

The American University in CairoComputer Science and Engineering Department

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Introduction to Computer Systems

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Origins of Computing Machines

• Early computing devices– Abacus: positions of beads represent numbers– Gear-based machines (1600s-1800s)• Positions of gears represent numbers• Blaise Pascal, Wilhelm Leibniz, Charles Babbage

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Figure 0.3 An Abacus

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Early Data Storage

• Punched cards– First used in Jacquard Loom (1801) to store

patterns for weaving cloth– Storage of programs in Babbage’s Analytical Engine– Popular through the 1970’s

• Gear positions

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Early Computers

• Based on mechanical relays– 1940: Stibitz at Bell Laboratories– 1944: Mark I: Howard Aiken and IBM at Harvard

• Based on vacuum tubes– 1937-1941: Atanasoff-Berry at Iowa State– 1940s: Colossus: secret German code-breaker– 1940s: ENIAC: Mauchly & Eckert at U. of Penn.

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Figure 0.4 The Mark I computer

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Personal Computers

– First used by hobbyists– IBM introduced the PC in 1981.• Accepted by business• Became the standard hardware design for most desktop

computers• Most PCs use software from Microsoft

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Terminology

• Hardware: Equipment

• Software: Programs and algorithms

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Computer Architecture

• Central Processing Unit (CPU) or processor– Arithmetic/Logic unit versus Control unit– Registers• General purpose• Special purpose

• Bus• Motherboard

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Figure 2.1 CPU and main memory connected via a bus

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Memory Terminology

• Random Access Memory (RAM): Memory in which individual cells can be easily accessed in any order

• Dynamic Memory (DRAM): RAM composed of volatile memory

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Main Memory Addresses

• Address: A “name” that uniquely identifies one cell in the computer’s main memory– The names are actually numbers.– These numbers are assigned consecutively starting

at zero.– Numbering the cells in this manner associates an

order with the memory cells.

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Bits and Bit Patterns

• Bit: Binary Digit (0 or 1)• Bit Patterns are used to represent information.– Numbers– Text characters– Images– Sound– And others

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Main Memory Cells

• Cell: A unit of main memory (typically 8 bits which is one byte)– Most significant bit: the bit at the left (high-order)

end of the conceptual row of bits in a memory cell– Least significant bit: the bit at the right (low-order)

end of the conceptual row of bits in a memory cell

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Figure 1.7 The organization of a byte-size memory cell

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Figure 1.8 Memory cells arranged by address

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Measuring Memory Capacity

• Kilobyte: 210 bytes = 1024 bytes– Example: 3 KB = 3 times1024 bytes– Sometimes “kibi” rather than “kilo”

• Megabyte: 220 bytes = 1,048,576 bytes– Example: 3 MB = 3 times 1,048,576 bytes– Sometimes “megi” rather than “mega”

• Gigabyte: 230 bytes = 1,073,741,824 bytes– Example: 3 GB = 3 times 1,073,741,824 bytes– Sometimes “gigi” rather than “giga”

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Mass Storage

• On-line versus off-line• Typically larger than main memory• Typically less volatile than main memory• Typically slower than main memory

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Mass Storage Systems

• Magnetic Systems– Disk– Tape

• Optical Systems– CD– DVD

• Flash Drives

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Figure 1.9 A magnetic disk storage system

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Representing Text

• Each character (letter, punctuation, etc.) is assigned a unique bit pattern.– ASCII: Uses patterns of 7-bits to represent most

symbols used in written English text– Unicode: Uses patterns of 16-bits to represent the

major symbols used in languages world side– ISO standard: Uses patterns of 32-bits to represent

most symbols used in languages world wide

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Representing Numeric Values

• Binary notation: Uses bits to represent a number in base two

• Limitations of computer representations of numeric values– Overflow – occurs when a value is too big to be

represented– Truncation – occurs when a value cannot be

represented accurately

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The Binary System

The traditional decimal system is based on powers of ten.

The Binary system is based on powers of two.

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Figure 1.15 The base ten and binary systems

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Figure 1.16 Decoding the binary representation 100101

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Figure 1.17 An algorithm for finding the binary representation of a positive integer

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Figure 1.18 Applying the algorithm in Figure 1.15 to obtain the binary representation of thirteen

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Figure 1.19 The binary addition facts

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Figure 2.2 Adding values stored in memory

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Figure 2.3 Dividing values stored in memory

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Boolean Operations

• Boolean Operation: An operation that manipulates one or more true/false values

• Specific operations– AND– OR– NOT

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Figure 1.1 The Boolean operations AND and OR

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Stored Program Concept

A program can be encoded as bit patterns and stored in main memory. From there, the CPU can then extract the instructions and execute them. In turn, the program to be executed can be altered easily.

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Terminology

• Algorithm: A set of steps that defines how a task is performed

• Program: A representation of an algorithm• Programming: The process of developing a

program

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Low Level LanguageFirst Generation Language

• Machine instruction: An instruction (or command) encoded as a bit pattern recognizable by the CPU

• Machine language: The set of all instructions recognized by a machine

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Machine Instruction Types

• Data Transfer: copy data from one location to another

• Arithmetic/Logic: use existing bit patterns to compute a new bit patterns

• Control: direct the execution of the program

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Program Execution

• Controlled by two special-purpose registers– Program counter: address of next instruction– Instruction register: current instruction

• Machine Cycle– Fetch– Decode– Execute

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Figure 2.8 The machine cycle

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Ethical Theories

• Consequence based:What leads to the greatest benefit?

• Duty based:What are my intrinsic obligations?

• Contract based:What contracts must I honor?

• Character based:Who do I want to be?