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#operating-systems

some piece of software that manages the hardware
- do?: memory management, I/O management, scheduling, communication, multi-tasking, ...
special layer of software that provides application software access to hardware resources
Kernel: The one program running at all times on the computer
provides an easy to use simple interface to interact with devices and use applications through consistent abstractions
- We take a lot of things for granted these days. However most tasks occur through complex interactions of multiple components in multiple administrative domains (Web Search: DNS Request, DNS Servers, route through internet, data centre, load balancer, search, retrieve from page store, create result page and then show result)
User applications help solve computing problems using the same set of hardware, i.e. hardware resources are shared between multiple programs and thus need to be managed and allocated carefully + efficiently + safely
- Robustness requires an engineering mindset: Meticulous error handling, defending against malicious or careless users
Key Building Blocks:
- Processes
- Threads, Concurrency, Scheduling, Coordination
- Address Space
- Protection, Isolation, Sharing Security
- Communication, Protocols
- Persistent Storage, Transactions, Consistency, Resilience
- Interface to all devices
Processor: Interface -> Threads
For an OS area we can ask the following:
- What hardware interface to handle? (physical reality)
- What software interface to provide? (nicer abstraction)

Process (managing the CPU)

Execution environment with restricted rights provided by OS
What's in a process?:
- Address Space
- one or more threads of control executing in that address space
- additional state(open files, open sockets, ...)
provide nicer interface than raw hardware
OS isolates processes from each other
OS isolates itself from other processes

... even though they are running on the same hardware

a single core CPU can only run a single program at a time, if multiple applications need to be run then they must share the resource (time sharing) i.e. there is a illusion of a private CPU for each program
Scheduling: allocate CPU time to different processes
- each process must get time on the CPU
- priorities must be respected
- should be able to handle multiple cores
- overhead of switching processes must be low
- CPU utilisation must be high, i.e. must be busy all the time; minimise waiting time

Address Space (managing the memory)

Interface: Address Space
memory interactions are either read or write operations
a virtual address space is created for each process giving the illusion of access to the full physical address space

Device Drivers (managing I/O)

From the perspective of an OS, an I/O device is just a bunch of registers
each device will have its own unique and complex interface, the OS defines a single uniform interface for all devices and it becomes the responsibility of the device driver to talk with the device controller
3rd party device drives are one of the most unreliable aspects of OS
- Poorly written by non-stake holders
- Ironically, the attempt to provide clean abstractions can lead to crashes

idx

Process (managing the CPU)

Address Space (managing the memory)

Device Drivers (managing I/O)

Files & Directories (managing storage)

Network

References