Operating Systems: Crash Course Computer Science #18

Summary

This episode explores the evolution of operating systems, from early computers running single programs to modern OSes like Mac OS X and Windows 10. It discusses the advent of batch processing, device drivers, multitasking, virtual memory, and memory protection, highlighting key developments like the Atlas Supervisor and Unix, and the shift to personal computers.

Takeaways

• 💻 In the 1940s and early 1950s, computers ran one program at a time, with programs manually loaded by operators.
• 🚀 As computers became faster, the manual process of loading programs became inefficient, leading to the development of operating systems.
• 🌐 Operating systems (OS) are programs that manage other programs and have special privileges on the hardware, typically starting first when a computer is turned on.
• 📚 The first operating systems in the 1950s introduced batch processing, allowing computers to run multiple programs automatically without downtime.
• 🔄 As computers spread, the challenge of writing code for different computer configurations led to the need for operating systems to act as intermediaries, providing device drivers for standardized hardware interaction.
• 🖨 By the end of the 1950s, computers were often idle due to slow I/O operations. The Atlas Supervisor, developed in the 1960s, introduced multitasking by scheduling multiple programs to run concurrently on a single CPU.
• 🧩 To manage multiple programs running simultaneously, operating systems allocated each program its own block of memory, introducing the concept of dynamic memory allocation.
• 🔒 Memory protection was also introduced to isolate programs from each other, preventing a buggy program from affecting others and protecting against malicious software.
• 🌐 The Atlas computer was the first to support virtual and protected memory, enhancing the flexibility and security of multitasking.
• 📈 By the 1970s, operating systems like Multics and Unix were developed to support time-sharing, allowing multiple users to interact with a computer simultaneously, with Unix emphasizing a lean kernel and user-contributed tools.
• 🏠 The advent of personal computers in the 1980s required simpler operating systems like MS-DOS, which, despite lacking multitasking and protected memory, became popular due to its small size and compatibility with early home computers.

Q & A

What was the primary limitation of computers in the 1940s and early 1950s in terms of running programs?

Computers in the 1940s and early 1950s could only run one program at a time, and the process of loading programs was very manual, involving writing code on punch cards and handing them to a computer operator to be fed into the computer when it was available.

Why was the development of operating systems necessary as computers became faster?

As computers became faster, the time taken by humans to insert programs manually into the computer was longer than the time taken to run the actual programs. Operating systems were needed to automate the process and allow computers to operate themselves more efficiently.

What is batch processing in the context of early operating systems?

Batch processing is a method where computers were given batches of programs to run instead of one at a time. Once one program finished, the computer would automatically and quickly start the next one, reducing downtime.

How did the advent of operating systems help with the issue of diverse computer configurations?

Operating systems acted as intermediaries between software programs and hardware peripherals, providing a software abstraction through APIs called device drivers. This allowed programmers to interact with common input and output hardware using standardized mechanisms, simplifying the process of writing code for different computer configurations.

What problem did the Atlas Supervisor solve in terms of computer usage?

The Atlas Supervisor, developed at the University of Manchester, allowed for multitasking by running several programs at the same time on a single CPU through clever scheduling. This maximized the use of the computer's resources, preventing idle time while waiting for slow mechanical processes like printing.

How does virtual memory help with the complexity of dynamic memory allocation?

Virtual memory allows programs to assume their memory always starts at address 0, simplifying the programming process. The operating system abstracts the actual physical memory locations, handling the remapping from virtual to physical addresses automatically.

What is memory protection and why is it important?

Memory protection is a feature that isolates each program in its own memory space, preventing a buggy program from affecting the memory of other programs. This is crucial for system stability and security, especially against malicious software.

What was the significance of the Multics operating system in the development of Unix?

Multics was an early time-sharing operating system designed with security in mind. However, it was considered over-engineered and complex. The experience with Multics led Dennis Ritchie and Ken Thompson to create Unix, which focused on a lean kernel and a collection of useful tools separate from the core OS.

Why was the simplicity of Unix's design a key factor in its popularity?

The simplicity of Unix's design allowed it to run on cheaper and more diverse hardware. It also made it easier for developers to contribute tools and programs, which contributed to its widespread adoption in the 1970s and 80s.

How did the early personal computers' operating systems differ from those used in larger mainframes?

Early personal computers' operating systems, such as MS-DOS, were much simpler and smaller in size compared to mainframe operating systems. They lacked features like multitasking and protected memory, which meant that programs could easily crash the system, but this was an acceptable tradeoff given the affordability and simplicity of personal computers at the time.

What modern operating systems have inherited features from the developments in operating systems over the decades?

Modern operating systems like Mac OS X, Windows 10, Linux, iOS, and Android have inherited features such as multitasking, virtual memory, and protected memory from the developments in operating systems over the decades. These features enable them to run many programs simultaneously and provide a stable and secure computing environment.