OS notes

Basically , links

Hyper-threading

Threads: User-level vs Kernel

User/Kernel Mode, Syscall, I/O, Exceptions

• The user-mode program places values in registers, or creates a stack frame with arguments, to indicate what specific service it requires from the operating system.
• The user-mode program then performs the trap instruction.
• Immediately, the CPU switches to kernel mode, and jumps to instructions at a fixed location in memory.
• These instruction, which are part of the operating system, have memory protections so that they cannot be modified by user-mode programs, and may also be unreadable by user-mode programs.
• The instructions, known as the trap or system call handler, read the details of the requested service + arguments, and then perform this request in kernel mode.
• With the system call done, the operating system resets the mode to user-mode and returns from the system call, or there is an instruction to do both at the same time.

https://stackoverflow.com/questions/19441823/a-file-opened-for-read-and-write-can-be-unlinked/19441923

https://www.guru99.com/mutex-vs-semaphore.html

https://en.wikipedia.org/wiki/Rate-monotonic_scheduling

https://www.geeksforgeeks.org/rate-monotonic-scheduling/

https://www.geeksforgeeks.org/earliest-deadline-first-edf-cpu-scheduling-algorithm/

https://www.geeksforgeeks.org/program-for-next-fit-algorithm-in-memory-management/