Operating System Concepts - Storage Hierarchy and Device Management

Mobile Computing

• Mobile computing has extra features such as GPS, gyroscope, and allows for new types of apps like augmented reality.
• Mobile devices use IEEE 802.11 wireless or cellular data networks for connectivity.
• Leaders in mobile operating systems are Apple iOS and Google Android.

Client-Server Computing

• Client-server computing is a model of distributed system where dumb terminals are replaced by smart PCs.
• The compute-server system provides an interface for clients to request services such as database access.
• The file-server system provides an interface for clients to store and retrieve files.

Peer-to-Peer (P2P) Computing

• P2P computing is another model of distributed system where nodes are considered peers.
• Peers can act as both clients and servers.
• Each node must join a P2P network and register its service with a central lookup service or broadcast requests for service via a discovery protocol.
• Examples of P2P systems include Napster, Gnutella, and Voice over IP (VoIP) systems like Skype.

Cloud Computing

• Cloud computing delivers computing, storage, and applications as a service across a network.
• It is a logical extension of virtualization, using virtualization as its base functionality.
• Cloud computing provides resources such as CPU, memory, I/O, and files as needed.

Process Management

• Creating and deleting both user and system processes.
• Suspending and resuming processes.
• Providing mechanisms for process synchronization, communication, and deadlock handling.
• Process management is responsible for reclaiming resources after process termination.

Memory Management

• Memory management determines what is in memory and when.
• It optimizes CPU utilization and computer response to users.
• Activities include:
  • 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.

File-System Management

• The OS provides a uniform, logical view of information storage.
• Files are usually organized into directories.
• Access control is used to determine who can access what.
• File-system management activities include:
  • Creating and deleting files and directories.
  • Primitives to manipulate files and directories.
  • Mapping files onto secondary storage.
  • Backing up files onto stable storage media.

Mass-Storage Management

• Mass storage is used to store data that does not fit in main memory or data that must be kept for a long period.
• Proper management is critical.
• OS activities include:
  • Mounting and unmounting.
  • Free-space management.
  • Storage allocation.
  • Disk scheduling.
  • Partitioning.
  • Protection.

Caching

• Caching is an important principle performed at many levels in a computer.
• Information in use is copied from slower to faster storage temporarily.
• Faster storage (cache) is checked first to determine if information is there.
• Cache management is an important design problem.

I/O Subsystem

• The I/O subsystem is responsible for hiding hardware device peculiarities from the user.
• Activities include:
  • Memory management of I/O.
  • Buffering, caching, and spooling.
  • General device-driver interface.
  • Drivers for specific hardware devices.

Protection and Security

• Protection is any mechanism for controlling access to resources defined by the OS.
• Security is the 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, one per user.
• Group identifier (group ID) allows set of users to be defined and controls managed.

Virtualization

• Virtualization allows operating systems to run applications within other OSes.
• It is a vast and growing industry.
• Emulation is used when source CPU type is different from target type.

Multiprocessing

• Multiprocessing is a system that contains multiple processors.
• It provides:
  • Increased throughput.
  • Economy of scale.
  • Increased reliability – graceful degradation or fault tolerance.
• There are two types: asymmetric and symmetric multiprocessing.

Symmetric Multiprocessing Architecture

• Each processor performs all tasks.
• The OS is responsible for scheduling processes across processors.

Clustered Systems

• Clustered systems are like multiprocessor systems, but multiple systems working together.
• They usually share storage via a storage-area network (SAN).
• They provide:
  • High-availability service that survives failures.
  • Asymmetric clustering has one machine in hot-standby mode.
  • Symmetric clustering has multiple nodes running applications, monitoring each other.

PC Motherboard

• A PC motherboard is an example of a computer system.

Computer System Environments

• There are several types of computer system environments:
  • Traditional.
  • Mobile.
  • Client-server.
  • Peer-to-peer.
  • Cloud computing.
  • Real-time.
  • Embedded.
  • Computing environments are becoming more interconnected.

Traditional Computing

• Traditional computing is characterized by stand-alone general-purpose machines.
• But, most systems interconnect with others (e.g., the Internet).
• Portals provide web access to internal systems.
• Network computers (thin clients) are like Web terminals.
• Mobile computers interconnect via wireless networks.
• Networking is becoming ubiquitous – even home systems use firewalls to protect home computers from Internet attacks.

Mobile Computing

• Mobile computing is characterized by handheld devices such as smartphones and tablets.
• Mobile devices interconnect via wireless networks.

Storage Hierarchy

• The storage hierarchy is organized by speed, cost, and volatility.
• Caching is copying information into faster storage system.
• Device drivers are used to manage I/O.

Storage-Device Hierarchy

• The storage-device hierarchy is a hierarchical organization of storage devices.

How a Modern Computer Works

• A modern computer works using a von Neumann architecture.
• The CPU fetches instructions from memory and executes them.

Direct Memory Access Structure

• Direct memory access is used for high-speed I/O devices.
• The device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention.

Operating-System Operations

• The bootstrap program is a simple code that initializes the system and loads the kernel.
• The kernel loads, starts system daemons, and kernel interrupt-driven.
• Hardware interrupts are generated by devices.
• Software interrupts are generated by software errors or requests for operating system service.

Multiprogramming

• Multiprogramming is a system that organizes jobs (code and data) so that the CPU always has one to execute.
• When a job has to wait, the OS switches to another job.

Multitasking

• Multitasking is a logical extension of batch systems.
• The CPU switches jobs so frequently that users can interact with each job while it is running.
• Response time should be less than 1 second.
• Each user has at least one program executing in memory.
• CPU scheduling is used to schedule jobs.

Memory Layout for Multiprogrammed System

• The memory layout for a multiprogrammed system includes multiple jobs running concurrently.

Dual-mode Operation

• Dual-mode operation allows the OS to protect itself and other system components.
• The mode bit is used to distinguish between user mode and kernel mode.
• Privileged instructions are only executable in kernel mode.
• System calls are used to change the mode to kernel mode.

Timer

• The timer is used to prevent infinite loops.
• The timer is set to interrupt the computer after some time period.
• The OS sets the timer (privileged instruction).
• When the timer is zero, an interrupt is generated.

Process Management

• A process is a program in execution.
• It is a unit of work within the system.
• Process management is responsible for creating, deleting, suspending, and resuming processes.
• It is also responsible for providing mechanisms for process synchronization, communication, and deadlock handling.