A computer is an electronic device that can be programmed to automatically carry out sequences of arithmetic or logical operations (computation)

The principle of the modern computer was coined by Alan Turing in 1936

Universal Turing machine:

• Read & write symbols on an infinite tape according to a set of rules defined by its transition function
• It moves its read/write head left or right and changes its state based on the current symbol and state

A physical Turing machine

A LEGO Turing machine (ENS Lyon)

A Turing machine in Minecraft

Turing machines describe an abstract machine

How can we go from this idealized model to a real computer?

Describing computer systems or architectures

• The von Neumann architecture (or Princeton architecture)
• The Harvard architecture
• The modified Harvard architecture

Modified Harvard architecture

• Used in modern computers and microcontrollers

• Separate mdata and instruction caches

• Unified memory addressing (but separate pathways or caches)

• Flexibility

• Performance optimization

A lot more input/output peripherals

Sending binary instructions to a computer is possible though not practical

$\rightarrow$ Use a primary software called the operating system (OS) to act as an intermediary between users and the computer hardware

Another trip down memory lane

• Early computers (1940s – 1950s):

  • Manual operations, batch processing

• Mainframe era (1960s):

  • Transition from single-user, single-task systems to multi-user, multitasking environments

• Unix and early minicomputers (1970s):

  • Portability, Hierarchical file-system, security and permissions

• Personal computers (1980s):

  • Simpler, more intuitive, and capable of running on less powerful hardware
  • Introduction of the Graphical User Interface (GUI) by Apple

Rise of modern operating systems

• Microsoft Windows:

  • 3.0 to 95 pivotal in establishing Microsoft as the dominant desktop operating system
  • Windows NT/2000/XP and beyond provided stability and usability

• GNU/Linux – the open-source revolution:

  • 1991: first version of the Linux Kernel
  • By the 2000s, Linux dominate in the server market and more

• MacOS:

  • Unix based core
  • Strong link to Apple hardware

Rise of modern operating systems

• Hardware resource management is under the responsibility of the kernel

• Keys functions of the kernel are:

  • Process management
  • Memory management
  • Device management
  • File system management
  • Inter process communication
  • Security and access control

Command-line shells

• Historical way to interact with the OS
• Command-line shells require users to input textual commands to perform tasks such as file management, process control, etc.
• Examples: sh, bash, zsh, cmd.exe, Powershell

Graphical shells

• Allows the access to the functions of an operating system without having to type-in commands
• Often built on top of what is called a windowing system
• Examples: Gnome Shell, Windows shell, Aqua

The Init program

• The first program to run after the kernel is loaded

Daemons and services

• Background tasks that performs specific functions (awaiting connections, monitoring the computer)

Users

• Human users – Regular or administrator/root
• Service accounts – used by the OS to run specific tasks (e.g., www-data)

The standard format of a command

<prompt> <command> <param_1> <param_2> <param_3> ... <param_N>

• <prompt> – Generated by the program to provide context for the user (it usually ends with one of the characters $, %, #, :, > or _)

• <command> – Provided by the user. It can be:

  • Internal or built-in commands
  • External commands to run executables

• <param_1> ... <param_N> – Parameters provided by the user, if needed

A computer is an electronic device that can be programmed to automatically carry out sequences of arithmetic or logical operations (computation)

• Computer consists in multiple hardware components such as the CPU, RAM modules, Storage devices connected through a Motherboard

• To use a computer the user needs an operating system

• Terminals are still very much present on modern computers and a quick and simple way to interact with the computer