Operating System Concepts: Multiprocessing

Multiprocessor Systems

• Increased throughput can be achieved through multiprocessor systems.
• Two types of multiprocessor systems:
  • Asymmetric Multiprocessing
  • Symmetric Multiprocessing

Clustered Systems

• Like multiprocessor systems, but multiple systems work together.
• Usually share storage via a storage-area network (SAN).
• Provides a high-availability service that survives failures.
• Two types of clustering:
  • Asymmetric clustering: one machine in hot-standby mode.
  • Symmetric clustering: multiple nodes running applications, monitoring each other.

Operating System Structure

• Multiprogramming is needed for efficiency.
• A subset of total jobs in the system is kept in memory.
• One job is selected and run via job scheduling.
• When a job has to wait (e.g. for I/O), the OS switches to another job.
• Timesharing (multitasking) is a logical extension of multiprogramming.
• Response time should be less than 1 second.
• Each user has at least one program executing in memory (a process).
• If several jobs are ready to run at the same time, CPU scheduling is used.
• If processes don't fit in memory, swapping moves them in and out to run.
• Virtual memory allows the execution of processes not completely in memory.

Process Management

• A process is a program in execution.
• Process management activities:
  • Creating and deleting processes
  • Suspending and resuming processes
  • Providing mechanisms for process synchronization
  • Providing mechanisms for process communication
  • Providing mechanisms for deadlock handling

Interrupt Handling

• The operating system preserves the state of the CPU by storing registers and the program counter.
• Determines which type of interrupt has occurred.
• Separate segments of code determine what action should be taken for each type of interrupt.
• Interrupt handling involves:
  • Polling
  • Vectored interrupt system

I/O Structure

• Two types of I/O structures:
  • Wait instruction idles the CPU until the next interrupt.
  • System call – request to the operating system to allow the user to wait for I/O completion.

Storage Hierarchy

• Storage systems are organized in a hierarchy.
• Cache: copying information into faster storage system.
• Main memory: only large storage media that the CPU can access directly.
• Secondary storage: extension of main memory that provides large nonvolatile storage capacity.

Computer-System Architecture

• Most systems use a single general-purpose processor.
• Multiprocessors systems are growing in use and importance.
• Advantages of multiprocessors:
  • Increased throughput
  • Economy of scale
  • Increased reliability – graceful degradation or fault tolerance

Memory Management

• Memory management activities:
  • Keeping track of which parts of memory are currently being used and by whom.
  • Deciding which processes and data to move into and out of memory.
  • Allocating and deallocating memory space as needed.

Storage Management

• OS provides a uniform, logical view of information storage.
• Abstracts physical properties to logical storage unit - file.
• File-System management:
  • Creating and deleting files and directories.
  • Primitives to manipulate files and directories.
  • Mapping files onto secondary storage.
  • Backup files onto stable storage media.

Mass-Storage Management

• Proper management of mass storage is of central importance.
• OS activities:
  • Free-space management.
  • Storage allocation.
  • Disk scheduling.
• Some storage need not be fast, such as tertiary storage.

Performance of Various Levels of Storage

• Movement between levels of storage hierarchy can be explicit or implicit.
• Importance of cache coherency in hardware.

I/O Subsystem

• I/O subsystem responsible for:
  • Memory management of I/O, including buffering, caching, and spooling.
  • General device-driver interface.
  • Drivers for specific hardware devices.

Protection and Security

• Protection: any mechanism for controlling access of processes or users to resources defined by the OS.
• Security: defense of the system against internal and external attacks.
• Systems distinguish among users to determine who can do what.
• User identities (user IDs, security IDs) include name and associated number.
• Access control includes user ID, group ID, and privilege escalation.