History of Programming Language

Summary

This video traces the evolution of programming, from early machine code and punch cards to the introduction of terminals, electronic displays, and assembly languages. It explores the tedious process of writing machine code directly, and how assembly language, specific to processors and operating systems, made programming more efficient. The video also explains the assembly process, including how object files and linkers create executable files. Finally, it highlights the benefits of dynamic linking and shared libraries, emphasizing how they optimize memory usage in modern operating systems.

Takeaways

• 💻 A computer program ultimately consists of machine code—binary instructions that the CPU reads and executes directly.
• 🕰️ In the 1940s, programming was done manually by flipping switches and rearranging vacuum tube plugs, making it extremely slow and tedious.
• 🗂️ Punch cards were introduced to store programs, allowing code to be reused without manually re-entering each instruction every time.
• ⌨️ In the 1960s, computer terminals combined keyboards with text displays, making it possible for users to interact with computers more directly.
• 🧲 Magnetic tape and electronic terminals enabled programmers to read and write code as text directly on computers for the first time.
• 🔢 Hex editors allowed programmers to write machine code byte by byte in hexadecimal, but this method was still cumbersome and impractical.
• 🛠️ Assembly language improved programming by representing machine instructions with human-readable mnemonics like 'add' instead of raw binary.
• 🔄 Assembly code must be translated into machine code through a process called assembly, performed by a program known as an assembler.
• ⚙️ Assembly language is processor-specific, meaning code written for one CPU architecture (like x86) will not work on another (like ARM).
• 🖥️ Assembly code is also operating-system-specific, so assembly written for Linux may not run on Windows even on the same processor.
• 📄 The text version of assembly written by a programmer is called source code, and it must be assembled into machine-readable object files.
• 🧩 An assembler produces object files, not executable programs; object files must be passed to a linker to create the final executable.
• 🔗 The linker combines multiple object files into one executable and resolves address references between separately assembled files.
• ⚡ Keeping assembly and linking separate improves efficiency because only changed source files need to be reassembled before relinking.
• 📚 Modern operating systems support dynamic linking, allowing programs to load code from shared libraries at runtime instead of embedding everything in one executable.
• 🪟 On Windows, shared libraries are called DLLs, while on Linux they are known as shared object files.
• 💾 Shared libraries reduce memory usage because multiple running programs can share a single copy of common code in physical memory.
• 🌐 Although shared libraries appear in each process’s virtual address space, the actual code is stored only once in physical memory.

Q & A

What is the main function of machine code in a computer program?

Machine code consists of binary instructions that are executed directly by the CPU to perform the operations of a computer program.

How were early computer programs inputted in the 1940s?

In the 1940s, programs were input by flipping switches and moving vacuum tube plugs, which was a very manual and cumbersome process.

What is a punch card and how did it help in programming?

A punch card is a thick piece of paper with perforated holes that represent data. It allowed programs to be stored and fed into machines automatically, though handling stacks of punch cards was still quite tedious.

What role did electronic terminals play in the 1960s?

In the 1960s, electronic terminals with keyboards and text displays allowed users to directly read and write text on computers, moving away from punch cards and paper outputs.

What is a hex editor and why is it impractical for writing machine code?

A hex editor allows users to create and edit files in binary using hexadecimal notation. While possible, it’s impractical for writing machine code due to its cumbersome and tedious nature.

What is assembly language and how does it relate to machine code?

Assembly language uses human-readable mnemonics to represent binary machine code instructions. It simplifies writing programs, but it still needs to be translated into binary by an assembler.

What does the term 'assembly language' imply, and how is it processor-specific?

Assembly language refers to low-level programming languages specific to a processor's architecture. Each processor type (e.g., x86, ARM) has its own unique assembly language, meaning assembly code written for one processor won’t work on another.

What is the role of an assembler in programming?

An assembler translates assembly language code (written by the programmer) into machine code that the computer can execute.

Why are object files and linkers used in the compilation process?

Object files are intermediate files produced by the assembler. A linker is then used to combine these object files into a single executable, resolving dependencies between different code modules.

What is the advantage of dynamic linking over static linking in modern operating systems?

Dynamic linking allows multiple programs to share common libraries, saving memory by loading only one copy of a shared library into physical memory, rather than embedding all the code into each executable file.