Computer Systems Fundamentals
- 2. Logic Gates
- 3. AND Gate A B Output 0 0 0 0 1 0 1 0 0 1 1 1 Truth Table
- 4. OR Gate A B Output 0 0 0 0 1 1 1 0 1 1 1 1 Truth Table
- 5. NOT Gate A Output 0 1 1 0 Truth Table
- 6. Conversions
- 7. Conversion Table DENARY HEXADECIMAL BINARY 1 1 0001 2 2 0010 3 3 0011 4 4 0100 5 5 0101 6 6 0110 7 7 0111 8 8 1000 9 9 1001 10 A 1010 11 B 1011 12 C 1100 13 D 1101 14 E 1110 15 F 1111
- 8. Hex to Denary Example Hex = 1EC Denary = (1x16^2) + (14x16^1) + (12x16^0) = 256 + 224 + 12 = 492
- 9. Denary to Hex Examples 128 64 32 16 8 4 2 1 Denary = 78 Binary = 01001110 Hex = 4E Denary = 232 Binary = 11101000 Hex = E8
- 10. Hex to Binary Examples FAB5 – 1111 1010 1011 0101 4CBF – 0100 1100 1011 1111 36ED – 0011 0110 1110 1101 9A7A – 1001 1010 0111 1010
- 11. Number Bases Binary = Base 2 Denary = Base 10 Hex = Base 16
- 12. Use Truth Tables with Binary NOT 10101010 = 01010101 NOT 11010110 = 00101001 10101010 AND 01010101 = 00000000 11101110 AND 00110110 = 00100110 10101010 OR 01010101 = 11111111 11010010 OR 01011001 = 11011011
- 13. Bits and Bytes Byte = 8 Bits Kilobyte = 1024 Bytes
- 14. Layers of the OS
- 15. User Interface • User interacts directly with OS here • Two interface types: • Graphic User Interface (GUI) • Command Line Interface (CLI) • Both are examples of Human Computer Interfaces (HCI) • Primary objectives to provide: • Input Capability – using keyboards, mouse etc. • Output Capability – using VDU, printers etc. • Load and run programs
- 16. File Management System • File Management System is responsible for: • Organising files • Managing files • Storage of data on: • Magnetic media (hard disks, floppy disks etc.) • Optical media (CD-ROM, DVD etc.) • USB Flash Drives
- 17. Input / Output Layer • Deals with physical interaction of software with outside world e.g.: • Disk drives, keyboards, printers, screens, mouse etc. • This software is known as “device drivers” • Layer also used for transferring the data to/from RAM/backing storage • In Windows, a device driver will have one of the following file extensions: • DLL – Dynamic Link Library – uses hardware interrupts • EXE – Executable – uses hardware interrupts • VXD – Virtual Device Driver – uses software interrupts
- 18. Memory Management Layer • Consists of loading a single program from a disk and allowing it free use of all available memory (RAM) • In Windows, multi-tasking is permitted; meaning more than one program can be loaded and run at the same time • Virtual Memory • Virtual memory is used when there is insufficient memory to run programs • Virtual memory is hard disk space set aside to act as memory • To the running programs, virtual memory is invisible; treats hard disk area as RAM • Protection • To stop programs from clashing with each other, each is tagged with information about which program ‘owns’ them. • If a program attempts to access memory segments it doesn’t have authority to access, it will be prevented.
- 19. Kernel • Properties • Most protected layer • Deepest layer • Most privileged layer • Acts a timekeeper and regulator of the system • Controls any time-slicing for multi-tasking functions • Ensures fairness in the way resources are allocated and used • Deals with interrupts having different properties, which arrive to signal external and internal events
- 20. API (Application Programming Interface) • An application programming interface (API) is a set of subroutine definitions, protocols, and tools for building application software. • In general terms, it is a set of clearly defined methods of communication between various software components.
- 21. ALU (Arithmetic Logic Unit) and Control Unit • Where data is processed and manipulated • ALU involves arithmetic operations and logical operations • ALU uses temporary registers to hold data • Accumulator is a main register which holds the results of calculations • Control Unit • Manages execution of instructions • Sends control signals around the computer
- 22. Registers • Memory Address Register (MAR) holds the address of a location in main memory • Memory Buffer Register (MBR) holds the data that has just been read from main memory or is to be written to main memory • Instruction Register (IR) holds the current instruction being executed • Program Counter (PC) holds the address of the next instruction to be fetched from memory
- 23. Buses • Data is transferred between memory and processors by buses: • Address Bus • Pinpoints memory location • One-Way Bus • Data Bus • Transfers the data • Two-Way Bus • Control Bus • Initiates and controls operations
- 24. ASCII • American Standard Code for Information Interchange • Represents 128 digits (0-127) (all characters on the keyboard)
- 25. Open-Source and Proprietary Software Open-Source – free to use, but training isn’t free Proprietary – paid for i.e. license agreements - Restrictions on use, not free to share