HERY H AZWIR Computer Software

Computer Software Outline Software and Programming Languages  Software  Programming  Programming language development  Software development program Software Engineering Operating System  O/S types  O/S functions  Various O/S products

Software System Software  Operating System (Windows, Linux, UNIX, etc)  Utilities Application Software  Business  Engineering  Education  Accounting  Statistics  Graphics, etc

Layers and Views of a Computer System

Software Characteristics Structured  Arranged according to certain rules of logic in such a manner that it describes the function(s) to be performed, the input(s) to the function(s) and the output(s) generated by the function(s) Created and Maintained  Transformation of human ideas into something that can operate the hardware within the computer  Once created the should be maintained during its life cycle  Two types:  Nonexecutable  Executable Machine Processible  It is intended to be processed by a machine  It must be matched to the particular computer chosen to run it

Programming Programming Language Type  Low Level  High Level Tools / Utilities  Editor  Translator  Object builder  Linker & Loader  Debugger Translator Type  Interpreter (one by one translation into machine code)  Assembler (assembly language translate into machine code)  Compiler (translate whole program into machine object code)

Programming Language Low Level  Assembly language: programmer can use mnemonic instruction codes, labels, and symbolic names for data, to refer directly to their machine code equivalents  More efficient in memory space and run faster  Very restricted set of syntactic rules

Programming Language High level language  To overcome difficulties in low level language  To make programming easier and available to larger technical and scientific community  One instruction in the source program usually generate a number of low level instructions to directly manipulate computer hardware Middle level language  Closer to low level language  Programming are easier than assembly language  Usually used by system programmers

Programming Language Example Middle level  C, C++, Ada. Modula High level  Scientific: FORTRAN, ALGOL, PASCAL  Data Processing: COBOL, DBASE,  Artificial Intelligence: LISP, PROLOG  General Purpose: PL/1, BASIC

Simple Software Development Program Problem -> Analyst -> Algorithm -> Create Program -> Editor -> Source Codes -> Assemble / Compile -> Object Module -> Linker (library routine) -> Loader -> Program Execution -> Correction -> Debugger -> Editor Finish Program

Tools / Utilities Editor  Write the text (source code) of the program by allowing the creation and modification of a source program file Translator  Assembler : software that translates an assembly language program into the machine code which can be executed by a processor. (one step process)  Compiler: software that translate a particular high /middle level language application program into its low-level machine language equivalent. (one step process)  Interpreter: software which directly translates instructions from a high level language to machine code, as the high level source code being executed. (step by step)  Run slower

Compiler Stages Lexical analysis  Removes redundant information, condenses statements, display error messages Syntactic analysis  Test correctness of the syntax of each line within the source program. Scans for errors in construction of the statements Code generation  If no errors detected then generate appropriate machine code for each statement or group of statements Optimization process  Increase the efficiensy of the object code

Tools / Utilities Linker  Responsible for connecting together all the different programming modules that have been written, including any library routines. Loader  Responsible for transferring the object code from an external medium to the microprocessor memory Debugger  To debug a program means to locate any software mistakes

Software Engineering Methodology Business Process Analysis System Requirements Specification Software Requirements Specification Software Design Coding (Implementation) Software Quality Assurance & Testing  Internal Testing (Integration, System, Stress, Load, etc)  User Acceptance Testing (UAT) System Deployment Documentation

Business Process Analysis Analyzing business process Explain the business process using method that can be understood by system analyst or system architect Use any kind tools such as  Flow chart  Data Flow Diagram (DFD)  Use – Case Diagram (UML)  Activity Diagram (UML)

System Requirements Specification Translate the explained business process into real system requirements  Computer resource requirements  Function and performance requirements  Safety, security, privacy protection requirements  Installation requirements  Design constraints  System environmental requirements  Operation and maintenance requirements  Other requirements (etc)

Software Requirements Specification Translate the system requirements into more detail software requirements  Functionality requirements  Performance requirements  Interface requirements  Environmental requirements  Security requirements  Data definition dan database requirements  Installation requirements  Operation and execution requirements  Maintenance requirements  Design and implementation constaraints  Documentation requirements  etc

Software Design Data Flow Diagram (Structured) Activity Diagram (Object oriented) Data Base design Entity-Relationship Diagram Normalization

Coding Chose programming language based on design constraint Writing, Editing Compiling, linking Executing Debuging Testing (unit testing, integration test) Documenting

Software Quality Assurance and Testing Integration test, System test, Stress test, Load test, etc Create:  Test plan  Test procedure  Test scenario Minimum:  Functionality test  Invalid data entry test (IDET) User acceptance test (UAT) Documentation

System Deployment Installation UAT

Operating System Example:  DOS  Windows  LINUX  MacOS  UNIX

Objectives and Functions Convenience  Making the computer easier to use Efficiency  Allowing better use of computer resources

Layers and Views of a Computer System

Operating System Services Program creation Program execution Access to I/O devices Controlled access to files System access Error detection and response Accounting

O/S as a Resource Manager

Types of Operating System Interactive Batch Single program (Uni-programming) Multi-programming (Multi-tasking)

Early Systems Late 1940s to mid 1950s No Operating System Programs interact directly with hardware Two main problems:  Scheduling  Setup time

Simple Batch Systems Resident Monitor program Users submit jobs to operator Operator batches jobs Monitor controls sequence of events to process batch When one job is finished, control returns to Monitor which reads next job Monitor handles scheduling

Memory Layout for Resident Monitor

Job Control Language Instructions to Monitor Usually denoted by $ e.g.  $JOB  $FTN ...Some Fortran instructions  $LOAD  $RUN ...Some data  $END

Desirable Hardware Features Memory protection  To protect the Monitor Timer  To prevent a job monopolizing the system Privileged instructions  Only executed by Monitor  e.g. I/O Interrupts  Allows for relinquishing and regaining control

Multi-programmed Batch Systems I/O devices very slow When one program is waiting for I/O, another can use the CPU

Single Program

Multi-Programming with Two Programs

Multi-Programming with Three Programs

Utilization

Time Sharing Systems Allow users to interact directly with the computer  i.e. Interactive Multi-programming allows a number of users to interact with the computer

Scheduling Key to multi-programming Long term Medium term Short term I/O

Long Term Scheduling Determines which programs are submitted for processing i.e. controls the degree of multi-programming Once submitted, a job becomes a process for the short term scheduler (or it becomes a swapped out job for the medium term scheduler)

Medium Term Scheduling Part of the swapping function (later…) Usually based on the need to manage multi- programming If no virtual memory, memory management is also an issue

Short Term Scheduler Dispatcher Fine grained decisions of which job to execute next i.e. which job actually gets to use the processor in the next time slot