intermezzOS workshop

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![rhizome](../public/images/rhizome.jpg)

## .subtitle[Wat is operating system?]

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# Nobody really can say

## .subtitle[Or rather, everyone can say?]

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# Three definitions

[Modern Operating Systems](https://www.amazon.com/Modern-Operating-Systems-Andrew-Tanenbaum/dp/013359162X):

> It is hard to pin down what an operating system is other than saying it is
> the software that runs in kernel mode—and even that is not always true. Part
> of the problem is that operating systems perform two basically unrelated
> functions: providing application programmers a clean abstract set of
> resources instead of the messy hardware ones and managing these hardware
> resources.

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# Three definitions

[Three Easy Pieces](http://pages.cs.wisc.edu/~remzi/OSTEP/):

1. Virtualization
2. Concurrency
3. Persistence

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# Three definitions

[Exterminate All Operating System Abstractions](https://people.eecs.berkeley.edu/~brewer/cs262b/hotos-exokernel.pdf):

> "software that securely multiplexes and abstracts physical resources"

But, uh...

> We believe that this denition specifically its view of the OS as an
> abstractor of hardware, is crippling and wrong.

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# abstractions

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![program-hardware](../public/images/program_hardware.png)

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![program-os-hardwares](../public/images/program_os_hardware.png)

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![program-vm-oss-hardwares](../public/images/program_vm_os_hardware.png)

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### We now have a pattern:

- ## I have `A`.
- ## `A` is written explicitly for `X`...
- ## ... but I want to support `X` and `Y`,
- ## <strong>so I put .highlight[abstraction] `B` in the middle.</strong>

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# isolation

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# "Kernel" vs. "Operating System"

- This is also a bit fuzzy
- "the software that runs in kernel mode", "even that is not always true"
- The kernel is the core of the operating system.

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# Kinds of kernels

- monolithic kernel
- microkernel
- exokernel
- unikernel

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# Common abstractions

These are some common abstractions provided by an operating system and/or kernel:

- address spaces
- memory protection
- processes
- files
- input/output devices

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# Some quick history

Another way to divide up kinds of kernels is through a sort of history:

- no OS
- batch OS
- single user
- multi user

Each of these changes caused new features to be required.

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# Some quick history

![core war](../public/images/corewar.png)