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Computing Environments CSC8304

Computing Environments CSC8304. Marcus Kaiser http://www.biological-networks.org. About this module. Module Leader: Dr Marcus Kaiser Today ’ s lecture – Introduction to Computing Environments

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Computing Environments CSC8304

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  1. Computing EnvironmentsCSC8304 Marcus Kaiserhttp://www.biological-networks.org

  2. About this module Module Leader: Dr Marcus Kaiser Today’s lecture – Introduction to Computing Environments Lectures for the next 4 weeks cover the need for database systems, statistical packages, security and poll-based/event-driven software Reading Week then follows – no lecture Remaining lectures cover programming languages, scripting and Perl Lectures are on Tuesdays, 9:30-11am, CLT.602 Lecture notes can be found on http://www.biological-networks.org/ (Training > Computing Environments for Bioinformatics ) Practical classes start in DAYSH.821 and are on Wednesdays 11-12am

  3. Assessment Coursework Databases/SQL 5 Nov deadline 15% of final mark Scripting/Perl 10 Dec deadline 15% of final mark Exam Exam January 70% of final mark

  4. A computing environment Requirements Enabling presentation of services to users and interaction with such services by users Monitors Tactile feedback devices Robots A world of supporting services Services Mobile devices (e.g., mobile phones) Video game consoles Printers

  5. A heterogeneous environment • A modern day computing environment is made up from many different types of enabling technologies. • An enabling technology refers to the mechanism that is used to implement a service. • Many technologies share the same ultimate goal (e.g., sending a message from one computer to another). • However, such technologies may attempt to achieve the same goal in different ways (e.g., Microsoft and Linux operating systems).

  6. Standards • There are instances when vendors must adhere to some standard to ensure integration (the Internet protocols exemplify this). • Standards play a crucial role in computer system development. • There are two types of standard: • Provided by an organisation that is recognised by the community as assuming the role of identifying standards (members of such an organisation are usually drawn from different vendors). • Provided by a vendor (or group of vendors) and deployed without international recognition (however, such recognition may occur at a later date).

  7. Computer technology evolution

  8. What if cars improved in a similar fashion?!!

  9. Conceptual Levels of Computers • A digital computer is capable of computation, communication and storage. • Computation is performed by carrying out instructions, a sequence of instructions to solve a problem is called a program • Instructions are recognised and executed by the electronic circuits in the computer • Instructions can only permit simple operations, typically, they can: • Add two numbers • Check if a number is zero • Move data around in Memory • This set of instructions is called the machine language • Different types of computers usually have different machine languages • The machine language is said to be the interface between the software and the hardware.

  10. Conceptual Levels of Computers contd. • Most users do not use machine language • Use high level language • e.g. Java • The high level language is translated to machine language by a compiler • Computers can be thought of as having different levels, each with its own language. • Each level carries out tasks on behalf of the level above it. • Helps to cope with understanding the complexity of computing systems Application Software (anybody) Software High Level Language (Java programmer) Operating System Level (programmer) Assembly Language Level (Assembly programmer) Software and/or Hardware Conventional machine level (hardware designer) Integrated circuit level (VLSI designer) Transistor level (Physical designer) Hardware Silicon + electronics level Chemical engineer

  11. Data Representation (1) • Humans count in base 10, using 10 digits • Difficult to represent electronically • Machines count in base 2 • Two-state devices are easy to make (transistors) • Only two digits used (0 and 1) called binary digits or bits • Electrically represented by 0 volts and 5 volts • Each bit occupies one memory cell or wire • The basic working unit consists usually of 8 bits, called a byte • The basic memory unit is a multiple number of bytes e.g. • 2 bytes = 16 bits • 4 bytes = 32 bits • 8 bytes = 64 bits • The basic memory unit is called the word length

  12. Data Representation (2) • All bytes in the memory are numbered, or addressable • The first byte is numbered 0, the second 1, and so on • Memory size is usually expressed in terms of (Mega)bytes • It is common practice to: • Write the least significant bit (LSB) on the right • Write the most significant bit (MSB) on the left • Start counting from zero • All data held within the computer is represented by a number of bits or bytes • All high level objects, such as a Java or C++ class must be translated into bits

  13. Data Representation (3) • Data comes in many forms • Booleans • Characters (i.e. text) • Integers, both positive and negative; e.g. -230, -1, 0, 45319 • Real numbers, also called floating point numbers, e.g. 3.0, log (13), sin(π/4), 22/7 • Structured data types defined by programming languages e.g. • Arrays • Strings • Classes • Each type is represented by one or more bits

  14. Byte Kilobyte (KB) Megabytes (MB) Gigabytes (GB) Terabytes (TB) = 8 bits = 1024 (210) Bytes = 220 Bytes = 230, or about a billion, Bytes = 240, or about a trillion, Bytes Bits, Bytes, and Buzzwords Terms used to describe file size or memory size:

  15. Integer data • Integer numbers don’t allow fractions • Humans use the decimal number system. There are 10 digits, 0 – 9. • Each place within a decimal number represents a power of 10. For example 236 = 2 * 102 + 3 * 101 + 6 * 100 + • 10 is not a ‘natural’ base (it is an anatomical incident!) • Computers work more naturally with base 2 because transistors have two states • In base 2, only digits 0 and 1 are used. Greatly simplifies the arithmetic and makes it much faster

  16. Binary Numbers • Each place within a binary number represents a power of 2. • e.g binary 101 = • 1 x 22 + • 0 x 21 + • 1 x 20 • (equals five in decimal) • Electrical representation: three wires ON OFF ON (5V) (0V) (5V)

  17. Binary Arithmetic • Humans perform decimal addition by: • Memorising all single-digit additions • Writing the numbers to be added down right-aligned, one above the other • Starting at the right and working towards the left • Adding the digits, writing down the result and propagating any carry to the next column • Subtraction works much the same way except that you must borrow from the next column • Multiplication with a single-digit number works much the same way too • Multiplication with a multi-digit number is treated as a series of separate single digit multiplications, the results of which are added together • Binary addition, subtraction and multiplication can treated exactly the same except that only the digits 0 and 1 are used.

  18. Basic Binary Arithmetic - examples

  19. Hexadecimal Numbers • Problem with binary arithmetic – Long strings are fine for machines but awkward for humans • e.g. What is the binary number 0100101011100011 ?? • Guess then work it out! • We (humans) therefore often use hexadecimal numbers (or hex for short). • This uses base 16. • There are 16 “digits” (0 1 2 3 4 5 6 7 8 9 A B C D E F) • Each place represents a power of 16: • e.g. 29F = 2 * 162 + 9 * 161 + F * 160 (=671 in decimal)

  20. Integer Representation • For the sake of economy, different hardware representations are used to implement different integer ranges • The following are commonly found:

  21. Integer overflow • It is possible that the result of an integer calculation is bigger than the allowed maximum (both positive and negative) • Look at the following 8-bit addition 11001000 200 -56 10010110 150 -106 -------------- ----- ------ (1)01011110 (256+) 94 (-256+) 94 • The final carry “disappears” because there is no hardware provision for it. The problem is called overflow (or underflow) • Is this serious? Would you like this to happen to your bank account? • Overflow is a serious problem. It indicates the presence of a bug in your program. The hardware can detect overflow and will cause your program to crash • Overflow occurred in the European Space Agency’s Ariane 5 rocket when the on-board software attempted to fit a 64 bit number into 16 bits. This did indeed cause the program to crash...

  22. Floating Point data • The range of possible values using 32 bits to represent a number, positive or negative, is large • However, bigger number representations are needed. • e.g. numbers to allow fractions and powers as required by many scientific applications • To represent fractions using integers, you would need two of them • One for the numerator and one for the denominator • Would be a major nuisance – not computationally amenable • The way to do this is to use floating point numbers. • Floating point data types allow a much greater range of possible values • They are represented in floating point notation

  23. Floating Point Notation • Details of how floating point values are represented vary from one machine to another. • The IEEE standard is one of the standard floating point representations • More info at http://www.cs.uaf.edu/~cs301/notes/Chapter4/node13.html

  24. Character Data • Used for textual data, but can represent small integers • Usually held in a byte although commonly only 7 bits are needed • There are two major character sets: • EBSIDIC (on IBM mainframe machines) • ASCII (on all other machines) • We concentrate on ASCII (American Standard Code for Information Interchange) • It has been standardised by ISO (International Standardisation Organisation) • ASCII was actually designed for use with teletypes and so the descriptions are somewhat obscure • Often ‘text’ documents are referred to as in ‘ASCII’ format – easier for document interchange

  25. ASCII • The characters are classed as • Graphic characters (printable or displayable symbols) • Control characters (intended to be used for various control functions, such as vertical motion and data communications. • The basic ASCII set uses 7 bits for each character, giving it a total of 128 unique symbols. • The extended ASCII character set uses 8 bits, which gives it an additional 128 characters. • The extra characters represent characters from foreign languages and special symbols for drawing pictures. More info @ http://www.jimprice.com/jim-asc.htm

  26. Unicode • Unicode is a new system to standardise character representation • Unicode provides a unique number for every character, independent of platform, program, or language • Adopted by such industry leaders as Apple, HP, IBM, JustSystem, Microsoft, Oracle, SAP, Sun, Sybase, Unisys. • Required by modern standards such as XML, Java, ECMAScript (JavaScript), LDAP, CORBA 3.0, WML • An implementation of the ISO/IEC 10646 standard • Enables Internationalization

  27. Unicode • How Unicode Works • It defines a large (and steadily growing) number of characters (> 110,000). • Each character gets a name and a number, e.g. LATIN CAPITAL LETTER A is 65 and TIBETAN SYLLABLE OM is 3840. • Includes a table of useful character properties such as "this is lower case" or "this is a number" or "this is a punctuation mark". • The Unicode standard also includes a large volume of helpful rules and explanations about how to display these characters properly, do line-breaking and hyphenation and sorting • Unicode is important – do some extra reading! – try a Google search

  28. Summary • A modern day computing environment is made up from many different types of enabling technologies • Standards are used to permit interoperability • Computers can be thought of as a number of different levels, ranging from the application software that we all use, right through to the electronic circuits within the computer • Computers count in binary • Various ways of representing numeric and character data

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