1. CSCI/CMPE 3334 Systems Programming
David Egle
Engr 3.296

2. Prerequisites CSCI/CMPE 2380 CSCI/CMPE 2333 Recommended – CSCI 2344
You will need to know about data structures such as linked lists and hashing
CSCI/CMPE 2333
Since we will be creating an assembler, the knowledge of assembly language is important
Recommended – CSCI 2344
The project is to be developed and run in the Linux system

3. Computer Software Application software
Concerned with using a computer to solve (create?) a problem
Focus is on the application (not the underlying hardware)
Generally machine independent
Examples:
Document preparation, spreadsheets, databases, statistical analysis, games, etc.

4. Computer Software (cont’d)
Systems software
Concerned with supporting the use and operation of the computer system
Provides tools for use by application software
Strongly machine dependent
Examples
Operating systems, assemblers, compilers, loaders/linkers, debuggers

5. System Software Without system software
all programming would be done in machine code
application programs would need to directly use hardware resources (I/O devices, storage, memory)
much of programmers time spent on program preparation and translation (and on finding effective ways to use hardware)

6. Programming environment
All of the hardware and software in the environment used by the programmer
A simple programming environment:
Text editor for program preparation
Assembler for translating programs to machine language
Simple operating system consisting of I/O drivers and a file system
This was typical of early timesharing systems

7. Improvements Use high level language
Implies other changes though!
Extensive library
Automatic storage management
Support for concurrency and exception handling
Sharing of resources between applications
More sophisticated operating systems
Attempt to protect users from damage caused by program developers or other users

8. Additional features to simplify programmer’s job
Library management
Modify contents of libraries of functions
Debugging tools
Allow run-time errors to be interpreted in terms of source program rather than machine code
Language specific text editors
“Knows” about program syntax
Finds syntax errors without leaving editor to compile program

9. Unifying framework
Two distinct components of all programming environments
Program preparation
Program execution

10. Bare machine Program preparation Program execution
Switches or buttons by which machine code and data is entered into the memory of the machine
Program execution
Hardware is directly manipulated
CPU
Peripherals
Memory

11. More advanced systems Program preparation Program execution
Text editors, assemblers, compilers, library managers, linkers, and loaders
Program execution
Operating system services, libraries of predefined functions, interpreters

12. History Earliest computers programmed in machine code
They were so expensive that using them for such clerical jobs as language translation was viewed as a dangerous waste of scarce resources!
Quickly realized the problems with this!
Letting the computer spend a few minutes on the clerical job of assembling a program was cheaper than hand assembling it and then spending hours of computer time debugging it!

13. History 2
By 1960
Assembly language widely accepted
High level languages being used
FORTRAN
COBOL
LISP
Algol
Compilers and program preparation tools commonly integrated into operating systems

14. History 3 Late 60’s, early 70’s
Saw separation of program preparation from program execution
Users obtained editors, compilers, operating systems from different vendors
Minicomputers and microcomputers followed history of mainframe programming
Primitive early systems with language being part of the operating system
Evolved to the more sophisticated systems of today

15. System Software and Architecture
System programs closely related to architecture of machine on which they are to run
The general design and logic of a system program usually does not depend on the target machine
The actual implementation will
So, we now consider the hardware aspect

16. Hardware considerations
Need to have an understanding of the characteristics of the hardware when creating systems software
Basic components of computer
CPU
Memory
I/O devices (includes storage)
Bus

17. CPU Instruction set Size and format of instructions Data format
Most of characteristics differentiating systems are found here
Instruction set
Size and format of instructions
Data format
Addressing schemes
Registers (size, number, usage)
Execution states
Interrupt handling
Multiprocessor

18. Memory Size of storage cells Number of cells Access methods
Instructions and data together or separate
Protection schemes
Cache handling

19. I/O and Bus I/O Bus Interface type (simple path, separate processor)
Access method (direct program control, DMA, I/O processor)
Bus
Determines speed at which information is passed between components
Bus size may influence programming – number of bits transferred at any one time
Dedicated or multiplexed

20. Why use hypothetical computer
Provides basis for study of systems software
Avoids problems which arise when using “real” computer systems
Cannot distinguish between “features” of systems software which are fundamental, and those which are the result of the idiosyncrasies of the hardware
See last section of each chapter for examples of systems software on different platforms