UF COP4600 - Exam 1 Questions and Answers 2024

Algorithm - set of instructions with finite initial store and state, a starting point, and unambiguous ordering until the endpoint Process (general definition) - a program in execution = program + state Program - sequence of instructions that embody an algorithm Job - a task to be completed Why need an O.S.? - - load program onto computer - access and supervise I/O devices - manage resources - protect private info - facilitate program interactions 2 main OS Roles? - 1. resource manager 2. extended machine 3 types of resource management - 1. process manager (who executes) 2. memory manager 3. I/O management Purpose of extended machine - allows user to not think about low-level things. (file storage for example) What OS is not? - - not UI - not development tools - not libraries (even if it may use them) 3 general OS types - - interactive (laptop/pc) - batch (priority is pre-defined queued tasks) - real time (well-defined task priorities like in avionics or cars) 5 generations of OS - '45-'55 : vacuum tubes / plugboards '55-'65 : transistors/batch '65-'80 : ICs and timesharing '80-now : PCs '90-now : mobile computers and multicore systems Multiprogramming v. Uniprogramming - multiple = 2+ programs' data concurrently in main memory (RAM) (uni is just 1 at a time) T/F: modern systems do not allow direct reads from the disk, rather a syscall is passed to the kernel which then returns the info (if allowed) - True 2 types of named calls - 1. procedure calls 2. system calls Procedure Calls - - essentially a function call - no context switch to kernel space (faster bc no OS help necessary) - local vars and parameters - frame pointer (where stack was before call) - stack pointer (where new bottom of stack is) Segments of Process in Memory - - TEXT(lowest): code being executed - DATA(middle growing up): static + dynamic - STACK(highest growing down): activation frames of calls System Calls - - provide interface to OS services - context switch to kernel mode - has sys lib entry point - invocation causes kernel trap - sys call number identifies a sysfunc from table - returns to library, returns to user program - parameters stored at specific mem. locations Hardware Interrupts - - hardware device sends interrupt request signal to the CPU through interrupt controller - CPU acks interrupt (implicitly checks for interrupts before each new instruction is loaded) - interrupt controller sends specific IRQ # - current CPU instruction interrupted and dispatcher finds correct handler, executes - CPU resumes in user mode - type of ASYNCHRONOUS TRAP Handle an interrupted interrupt process? - - solved with interrupt masks - a CPU feature that allows computer to ignore an interrupt request until mask bit is disabled - stores interrupt data in a (sometimes dedicated) register until ready - implement protection states that allow for hierarchical interrupting