Operating Systems Quiz I

What makes a computer?

processor, memory, I/O devices, system bus

registers

small, fast storage location within the CPU, data that needs quick access, holds operands for arithmetic and addresses for memory access

on cpu cache

small, high speed memory located inside/very close to the cpu, includes L1, L2, L3 caches, managed by cpu, avoids unnecessary read/write on BUS

main memory

large storage media that the cpu can access directly, volatile

secondary storage

non volatile slower memory, hdds and ssds

PC (Program Counter)

Keeps track of the memory address of the next instruction to be executed

IR (Instruction Register)

Holds the current instruction being executed

MAR (Memory Address Register)

Contains the address in memory that is to be read from or written to

MBR (Memory Buffer Register)

Temporarily holds data being transferred to or from memory

I/O AR (Input/Output Address Register)

Stores the address of a specific I/O device for communication

I/O BR (Input/Output Buffer Register)

Temporarily holds data being transferred to or from an I/O device.

Execution Unit

Executes instructions, performing calculation or operations as required.

Main memory

stores both instructions and data required for execution, memory location has an address (0,1,2, …, n-1), stored sequentially at lower addressed while data is stored at higher addresses

I/O module

handles communication between CPU and external devices, includes buffers to store data moving between devices

System Bus

transfers data, addresses, and control signals between components

Fetch Decode Execute Flow

PC → MAR → Memory → MBR → IR → Decode → Execute

Decode

Control unit decodes IR, figures out what operands/registers are needed and what to perform

Execute

Perform instruction, ALU/registers/memory do actual work, store result if needed

Fetch

Address of next instruction goes into MAR, instruction is fetched from memory into MBR, instruction moves to IR, PC moves to next instruction

abstraction

give applications a simple interface while hiding complicated details

resource managment

let the os decide how limited hardware resources are shared

isolation and protection

keeps programs separated, controls what they are allowed to access

API (Application Programming Interface)

defines interface at source code level, how software or programs interact

ABI (Application Binary Interface)

defines interface at binary level, specifying how compiled programs and libraries interact with the os or hardware

CPU time overhead

context switching, process scheduling, handling system calls

memory overhead

kernel code, device drivers, page tables, process control blocks

storage overhead

os binaries, system configurations, swap space, system logs

os abstractions

process, thread, file, socket, memory pages

os mechanisms

create, schedule, open, write, update, allocate, etc

policies

least recently used (LRU), FIFO, Shortest Job next (SJN), etc

kernel

core component of an operating system that interacts directly with the hardware

operating system

system software that provides an interface between user and hardware

program

static representation of operating and data, code, set of instructions to perform specific task stored on disk, passive entity

process

dynamic, instance of an active execution, active entity execution of a program in the memory

multiprogramming

technique in OS that allow multiple programs to reside in memory and execute concurrently by sharing system resources like cpu and memory, appearance of running multiple

pseudo paralellism

no true simultaneous execution of different programs

multiprogramming benefits

keeps cpu busy, reduces idle time, ensures resources are efficiently shared among multiple programs, multiple programs can progress simutanously.