Why computers use binary system?

• To achieve really fast speeds, electricity is the way to go!
• Representing 0's and 1's is really easy: is there an
  electrical current (ON) or isn't (OFF)?
• Current research for computers that can
  represent more digits (3 or 4)

What is the standard
architecture for computers?

• It's called the Von Neumann architecture
• The ALU do the calculations, the Control Unit controls the flow of information, the memory storages data and programs, input & output (i/o) interacts with user
• Nowadays the ALU and Control Unit are called the processsor /CPU

A CPU can do a limited
number of operations

• Move this value into a register, 
  Add two values on register store result into this register, 
  Go to line-memory #x, etc.
• Everything else is just a composition of those basic operations!

A CPU understands instructions

• A 0 or a 1 is called a bit
• 8-bits are called a byte
• Instruction are bytes that the CPU knows how to interpret (e.g. 00000010 means "sum")
• Each CPU has it's own Machine Language

Why we need
Operating Systems?

• They create an abstraction over the CPU

Programming is

• A set of instructions for a computer to execute
• This can be: sum these numbers, draw this to the screen, produce this sound, send this data to another computer, repeat this instruction until something else happens, etc.
• Anything you can define as an algorithm, can be programmable it's just a matter of time (which almost always implies money)

Programming Languages

• Were invented to be able to write on a more readable language
• They also are independent of the computer architecture
• But then, you need a translator to create machine code;
  the compiler

Usual process of
creating software

1. Write code in the programming language of your choice
2. Run a compiler to check if your syntax
   is valid while creating a better representation
   of your code to be consumed for a computer
3. Run a linker to create one file written
   on machine code
4. Run program, the computer will do as you say!

Different Computer 
Architecture uses different machine languages

If you want to run your program on a different OS you need to recompile

Supposedly, to recompile you wouldn't need to change your code!

• But in reality it wasn't always like that!
• People wanted something
  Write Once, Run Everywhere!

Interpreters to the rescue

• You write code on your programming
  language of choice
• A compiler produces intermediary
  code usually called bytecode
• That bytecode will be the same regardless of OS
• You run the bytecode using a virtual machine
• The virtual machine translate the bytecode to machine language

Compiled vs Interpreted
languages

• Compiled languages tend to be faster
• Interpreted languages don't need
  to be recompiled ever

Programming Paradigms

• Over time, people began creating best practices on how to program

• Some of this practices were unified in a paradigm.

• Some language are created with a paradigm in mind.

• There are 3 paradigms used on the industry: imperative, functional, object-oriented.

OOP has been since the '80s the predominant programming paradigm in the industry

C++

• It popularized OOP
• It was the successor to
  the most important imperative language: C
• It's still in use, but not in web development

Java

• It overtook C++ as the most popular
  OOP language
• It's interpreted; it's virtual machine
  is called the JVM It has been criticised
  as a verbose and old-fashioned language
• Since Java 8 it introduced some FP features
• It's now guided by from Oracle

C#

• OOP language created by Microsoft
• It's part of the .NET Framework,
  which is mostly for Windows
• It also has some FP features

Scala

• It's a JVM language that mixes OOP and FP
• It has become the 2nd most popular
  language on the JVM
• For years the industry has expected it to overthrow Java as the most used language on the JVM, but it has not happened yet
• It's guided by Typesafe

Javascript

• It's a language mainly used in front-end web development.
• It also mixes OOP and FP, although is a mostly misunderstood language.
• It's guided by the W3C (World Wide Web Consortium)