Information system lectures

1. Computer Software

2. Evolution of Programming
Languages
• Machine Languages
• Assembly Languages
• High-Level Languages
• Fourth-Generation Languages

3. Machine Languages
• The native language of the hardware
• Patterns of binary bits
• Machine specific, is non-portable
– is essentially the microcode of the processor

4. Assembly Languages
• Replace the pattern of binary bits with
– mnemonics for the commands
– variable names for memory locations
• Essentially a one-to-one mapping of the
machine language
• Still machine specific, is non-portable

5. High-Level Languages
• Represents multiple machine-level
statements with single statements
• Easier to learn and use
• Not machine specific, is portable

6. An Example
Machine Code Assembly Code High-Level Code
in Hex
27BB0001 ldah gp, main main()
23BD8050 lda gp, main {
23DEFFF0 lda sp, -16(sp) int a, b, c;
A61D8018 ldq r16, 8(gp) a = 3;
A77D8010 ldq r27, printf b = 4;
47E0F411 mov 7, r17 c = a + b;
B75E0000 stq r26, (sp) printf(“n%dn”, c);
6B5B4000 jsr r26, printf }
27BA0001 ldah gp, main
A75E0000 ldq r26, (sp)
23BD8050 lda gp, main
47FF0400 clr r0
23DE0010 lda sp, 16(sp)
6BFA8001 ret r26

7. Move from Language to
Language
• Computers only understand machine
language.
• Use an ASSEMBLER to convert a program
written in assembly language to machine
language.
• Use a COMPILER to convert a program
written in a high-level language to machine
language.

8. Executable Code
• Program code which is in machine language
and can be run (executed) by the computer
• Is hardware dependent you can’t run it on
just any machine
• On PCs PC usually have an EXE or a COM
extension

9. Object Code
• Program code which is in machine language
but which is not ready to be run (i.e. it is a
partial program).
• Is hardware dependent.
• On PCs usually has an OBJ extension.
• Not commonly used by end-users.

10. Source Code
• Program code which is written in a high-
level language.
• Cannot be run by the computer.
• Is usually a text file.
• File name extension usually reflects the
high-level language
– BASIC - BAS extension
– Pascal - PAS extension

11. Compiler & Files
Object Code
Executable
Code
Source
Code
Compiler
Linker
Object Code
Library
Error Messages
Program Listing

12. Dynamic Link Libraries
• Some Window programs use “run-time”
linking and and require the presence of
dynamic link library files which have a
DLL extension.
• DLL files ideally contain code which would
be used by a number of programs.

13. Object Libraries & DLLs
• Both contain “commonly” used code.
• With object libraries all the code is included
in the executable file at compile time so:
– programming effort is saved
– no space saving is realized, executables which
use common code have their own copy of the
library code

14. Object Libraries & DLLs
• With DLLs the code is “fetched” from the
DLL file at “run time” so:
– programming effort is saved
– space savings “may” be realized
– the more executables that use the library code
the greater the savings
– typically only a small part of the library code is
used

15. Common HLLs
• FORTRAN
• COBOL
• BASIC
• Pascal
• C
• C++
• PL/1
• Ada
• JAVA
• LISP
• Prolog

16. Fourth Generation Languages
• First three generations focused on
describing “HOW TO DO” a task.
• 4GLs focus on describing “WHAT TO
ACCOMPLISH”
• The fourth generation language compiler
must be able to translate the “what to
accomplish” description into a machine
level “how to” set of instructions.

17. Categories of 4GLs
• Query languages
• Report generators
• Graphics languages
• Application generators
• Very high-level programming languages
• Application software packages
• Microcomputer tools

18. Categories of Software
• System Software
– Operating Systems (OS)
– Language Translators
– Utility Programs
• Application Software

19. Operating Systems
• It is the job of the operating system to
manage the computers resources and control
the execution of programs.
• Computer resources include
– memory
– device drivers for peripheral devices
• The OS is the interface between the
hardware and the user/application program.

20. Layers of interaction
Hardware
System Software
Application Software
Users

21. Operating Systems
• OSs run the full spectrum from
– single program-single user, to
– multitasking, multi-user, with virtual memory
• The OS decides which program runs and for
how long.
• The OS improves throughput by skipping
over processes that are waiting for I/O.

22. Common Operating Systems
• CP/M
• DOS
• Windows 3.1
• Windows 95
• Windows NT
• OS/2
• System 7
• Mac OSX
• Linux
• UNIX
• VMS
• VM/CMS

23. More RAM needed!
• Newer OSs extend the capabilities of
desktop computers but require more RAM
• Windows 3.0 - 1MB (std),2MB (real)
• Windows 95 - 8MB recommended
• Windows NT 4.2 - 16MB (32 rec.)
• Windows 2000 - 64MB min.
• Windows XP - 128MB rec.(64MB min)
• Windows Vista - 1GB rec. (512MB min)