Operating Systems

Introduction Operating System A program that acts as an intermediary between a user of a computer and the computer hardware Operating system goals Ex

Firmware $$\\rightarrow$$ Bootloader $$\\rightarrow$$ OS kernelxv6: BIOS $$\\rightarrow$$ bootblock $$\\rightarrow$$ kernelLinux: BIOS/UEFI $$\\righta

Processes Running Dynamic Code Basic function of OS is to execute and manage code dynamically Command line terminal Icon double click Jobs/tasks run a

A server with many clientsA computer with many CPU coresSpace must be allocated for the new processfork() copies all state of the parentEach message h

N CPUs, P process/threadsIn what order should the process be run?On what CPU should each process run?Focus on scheduling in case of 1 CPUI/O bound or

Priority is CPU burst timeFCFS's priority is arrival timeRR's priority is dynamicalStarvationHigh priority tasks can dominate the CPU$$\\Rightarrow$$

Fair Share Scheduling New goal: Fairness From now on, schedulers are designed to optimize performance Minimize response time, turnaround time MLFQ achieves these goals, but complicated Non-trivial ...

Evil process can ruin other process or access kernel memoryCompiled programs include fixed pointer addressesEx) two copies of the same programProgram

Add BASE value to virtual addressIf translated address is bigger than BASE + BOUND,then Raise Protection ExceptionBASE and BOUND are protectedOnly cod

TLB

Swap frames between physical memory and diskLoad data from swap back into memory on-demandIf a process access a page that has been swapped out,page fa

Basics Dynamic allocation of pages Page table allows the OS to dynamically assign physical frames to process on-demand On Linux, processes use sbrk(), brk(), mmap() to request additional heap pages ...

Concurrency Concurrency vs Parallelism Concurrency Whether processes can access resources (CPU) simultaneously Parallelism Whether actually do multip

Construct for managing control flowCondition variables are not locksEach condition variable is associated with a mutexThreads that can't run yet wait(

Non-Deadlock Bugs Atomicity violation Desired serializability among multiple memory accesses is violated Two different threads access the field proc

Hard Disk Drive Geometry Hard drives expose a large number of sectors(blocks) Typically 512 or 4096 bytes(=page size -> easy to swap) Individual sector writes are atomic Multiple sectors writes...

How to cope with disk failureMechanical parts break over timeSectors may become silently corruptedCapacity is limitedManaging files across multiple ph

The cheapest way to store large amounts of dataSlowest component in most computersFragile mechanical components can breakDisk motor is extremely power