Three definitions

Modern Operating Systems:

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.

Three definitions

Three Easy Pieces:

1. Virtualization
2. Concurrency
3. Persistence

Three definitions

Exterminate All Operating System Abstractions:

"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.

We now have a pattern:

• I have A.

• A is written explicitly for X...

• ... but I want to support X and Y,

• so I put abstraction B in the middle.

"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.

Kinds of kernels

• monolithic kernel
• microkernel
• exokernel
• unikernel

Common abstractions

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

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

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.