Operating Systems Chapter 1: Computer System Overview Quiz

Computer System Overview

• An Operating System (OS) manages hardware resources, provides services to users, and manages secondary memory and I/O devices.

Basic Elements

• Processor (Central Processing Unit, CPU):
  • Controls the computer's operation
  • Performs data processing functions
• Main Memory (Real Memory, RAM):
  • Volatile, contents lost when the computer is shut down
  • Referred to as primary memory
• I/O Modules:
  • Moves data between the computer and external environments (e.g., storage, communications equipment, terminals)
• System Bus:
  • Provides communication among processors, main memory, and I/O modules

Top-Level View

• Microprocessor:
  • Invention that brought about desktop and handheld computing
  • Processor on a single chip
  • Fastest general-purpose processor
• Multiprocessors:
  • Each chip (socket) contains multiple processors (cores)

Instruction Execution

• A program consists of a set of instructions stored in memory
• Two steps: processor reads (fetches) instructions from memory, and processor executes each instruction
• Basic Instruction Cycle:
  • Processor fetches the instruction from memory
  • Program counter (PC) holds the address of the next instruction to be fetched
  • Instruction Register (IR) loads the fetched instruction
  • Processor interprets the instruction and performs required action

Interrupts

• Interrupt the normal sequencing of the processor
• Provided to improve processor utilization
• Most I/O devices are slower than the processor, causing the processor to pause and wait for the device
• Common classes of interrupts:
  • I/O completion
  • Timer expiration
  • Error detection
  • External events

Memory Hierarchy

• Major constraints: amount, speed, and expense
• Memory must keep up with the processor
• Cost of memory must be reasonable
• Memory relationships:
  • Greater capacity = smaller cost per bit
  • Faster access time = greater cost per bit
  • Greater capacity = slower access speed
• The Memory Hierarchy:
  • Decreasing cost per bit, increasing capacity, and increasing access time as you move down the hierarchy
  • Data is organized to minimize accesses to lower levels of memory

Secondary Memory

• Also referred to as auxiliary memory
• External, nonvolatile, and used to store program and data files
• Invisible to the OS
• Interacts with other memory management hardware

Cache and Main Memory

• Cache:
  • Small, fast memory
  • Contains a copy of a portion of main memory
  • Processor first checks cache
  • If not found, a block of memory is read into cache
• Cache/Main-Memory Structure:
  • Cache size
  • Number of cache levels
  • Block size
• Mapping Function:
  • Determines which cache location the block will occupy
  • Two constraints: replacement and search complexity
• Replacement Algorithm:
  • Least Recently Used (LRU) Algorithm
  • Effective strategy to replace a block that has been in the cache the longest with no references to it
• Write Policy:
  • Dictates when the memory write operation takes place
  • Can occur every time the block is updated or when the block is replaced
  • Minimizes write operations, leaving main memory in an obsolete state

Symmetric Multiprocessors (SMP)

• A stand-alone computer system with:
  • Two or more similar processors
  • Shared main memory and interconnected bus
  • Shared access to I/O devices
  • Integrated operating system controlling interactions between processors and programs

Multicore Computer

• Also known as a chip multiprocessor
• Combines two or more processors (cores) on a single piece of silicon (die)
• Each core consists of an independent processor, with additions like L2 cache and L3 cache in some cases