Computer Science 1JC3: Introduction to Computational Thinking - Lecture on Operating Systems and the Internet

Files

• Definition: A file is a finite sequence of data stored on a persistent storage device.
  • Data types: Characters or bits (values like true/false, yes/no, 0/1)
• Types of Files:
  • Text Files: ASCII or Unicode
  • Binary Files
  • File names often have extensions (e.g., .exe, .txt), but extensions can be incorrect or unnecessary.
• Importance:
  • Files allow sharing of data between programs, users, and storage devices.
  • Can be very large, sometimes only partially loaded into memory (e.g., video files).
• Functionality:
  • Used for input and output in programs, especially with large data amounts.

File Systems

• Set up by the operating system, organized as a tree with files and directories (also called folders).
• Directories: Hold files or other directories.
• Path Names:
  • Used to access files and directories.
  • Top level is "root" (e.g., in UNIX starts with a slash /).
  • Full and relative path names.
• File Operations: Creation, deletion, moving, copying, renaming, modification.

Processes

• Definition: An executing application program.
  • A program becomes a process when executed.
  • Multiple processes can execute the same program.
• Execution:
  • Processes run on CPU cores; modern computers have multiple cores.
  • Utilize time-sharing to run more processes than there are cores.
  • Time Slice: Short period of CPU time allocated to a process.
• Process States:
  • Executing, blocked (waiting for an event), ready (waiting for CPU), finished.
• Virtual Address Space:
  • Processes are given a virtual address space for memory, mapped to RAM or disk storage depending on execution.

Program Execution

• Parallel Execution: Appears parallel due to rapid switching of processes, but physically one process at a time on a single CPU.

Internet and Networks

• Physical Networks:
  • Computers exchange digital information via a physical medium.
  • Connected through network interfaces.
  • Types include wired, wireless, local area networks (LAN), wide area networks (WAN).
  • Topologies: Bus, ring, star, point-to-point.
  • Technologies: Ethernet, Wi-Fi, ATM, FDDI.

Internet Architecture

• Problem: Different physical networks needing communication.
• Solution: Universal virtual network built on top of physical networks.
  • Governed by TCP/IP protocol suite.
  • Internet architecture consists of interconnected physical networks via routers.
• Structure:
  • Two layers: heterogeneous physical networks and a homogeneous virtual network.
  • Addresses:
    • Physical network layer uses physical addresses.
    • Virtual network layer uses IP addresses.
    • Mapping of physical to virtual addresses is necessary.

Next Steps

• Next lecture will cover protocols that enable Internet functionality.