The American University in Cairo Computer Science and Engineering Department CSCE 106 Fundamentals of Computer Science Assisting Slides Introduction to Computer Systems 0 2 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 0 3 Figure 0 3 An Abacus 0 4 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 0 5 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 0 6 Figure 0 4 The Mark I computer 0 7 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 0 8 Terminology Hardware Equipment Software Programs and algorithms 0 9 Computer Architecture Central Processing Unit CPU or processor Arithmetic Logic unit versus Control unit Registers General purpose Special purpose Bus Motherboard 2 10 Figure 2 1 CPU and main memory connected via a bus 2 11 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 1 12 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 1 13 Bits and Bit Patterns Bit Binary Digit 0 or 1 Bit Patterns are used to represent information Numbers Text characters Images Sound And others 1 14 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 1 15 Figure 1 7 The organization of a byte size memory cell 1 16 Figure 1 8 Memory cells arranged by address 1 17 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 1 18 Mass Storage On line versus off line Typically larger than main memory Typically less volatile than main memory Typically slower than main memory 1 19 Mass Storage Systems Magnetic Systems Disk Tape Optical Systems CD DVD Flash Drives 1 20 Figure 1 9 A magnetic disk storage system 1 21 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 1 22 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 1 23 The Binary System The traditional decimal system is based on powers of ten The Binary system is based on powers of two 1 24 Figure 1 15 The base ten and binary systems 1 25 Figure 1 16 Decoding the binary representation 100101 1 26 Figure 1 17 An algorithm for finding the binary representation of a positive integer 1 27 Figure 1 18 Applying the algorithm in Figure 1 15 to obtain the binary representation of thirteen 1 28 Figure 1 19 The binary addition facts 1 29 Figure 2 2 Adding values stored in memory 2 30 Figure 2 3 Dividing values stored in memory 2 31 Boolean Operations Boolean Operation An operation that manipulates one or more true false values Specific operations AND OR NOT 1 32 Figure 1 1 The Boolean operations AND and OR 1 33 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 2 34 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 0 35 Low Level Language First 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 2 36 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 2 37 Program Execution Controlled by two special purpose registers Program counter address of next instruction Instruction register current instruction Machine Cycle Fetch Decode Execute 2 38 Figure 2 8 The machine cycle 2 39 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 0 40