Operating System Concepts - Multiprocessing

Computer Startup

• The bootstrap program is loaded at power-up or reboot, typically stored in ROM or EPROM (firmware).
• It initializes all aspects of the system and loads the operating system kernel, starting its execution.

Computer System Organization

• A computer system consists of one or more CPUs, device controllers connected through a common bus, providing access to shared memory.
• The system allows concurrent execution of CPUs and devices, competing for memory cycles.

Computer-System Operation

• I/O devices and the CPU can execute concurrently.
• Each device controller is in charge of a particular device type and has a local buffer.
• The CPU moves data from/to main memory to/from local buffers.
• I/O is from the device to the local buffer of the controller, and the device controller informs the CPU when it has finished its operation by causing an interrupt.

Interrupt Handling

• Interrupts transfer control to the interrupt service routine through the interrupt vector, which contains the addresses of all service routines.
• The interrupt architecture must save the address of the interrupted instruction.
• Incoming interrupts are disabled while another interrupt is being processed to prevent lost interrupts.
• A trap is a software-generated interrupt caused by an error or user request.
• An operating system is interrupt-driven.

Interrupt Timeline

• The operating system preserves the state of the CPU by storing registers and the program counter.
• It determines which type of interrupt has occurred, using polling or a vectored interrupt system.
• Separate segments of code determine what action to take for each type of interrupt.

I/O Structure

• After I/O starts, control returns to the user program either upon I/O completion or without waiting for I/O completion.
• In the first case, the wait instruction idles the CPU until the next interrupt, and at most one I/O request is outstanding at a time.
• In the second case, a system call is used to request the operating system to allow the user to wait for I/O completion.
• A device-status table contains an entry for each I/O device, indicating its type, address, and state.

Direct Memory Access Structure

• Used for high-speed I/O devices able to transmit information at close to memory speeds.
• The device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention.
• Only one interrupt is generated per block, rather than one interrupt per byte.

Storage Structure

• Main memory is the only large storage media that the CPU can access directly.
• Secondary storage is an extension of main memory, providing large nonvolatile storage capacity.
• Magnetic disks are rigid metal or glass platters covered with magnetic recording material.
• The disk surface is logically divided into tracks, which are subdivided into sectors.
• The disk controller determines the logical interaction between the device and the computer.

Storage Hierarchy

• Storage systems are organized in a hierarchy based on speed, cost, and volatility.
• Caching involves copying information into a faster storage system, and main memory can be viewed as a last cache for secondary storage.

Computer-System Architecture

• Most systems use a single general-purpose processor, but also have special-purpose processors.
• Multiprocessor systems are growing in use and importance, providing advantages such as increased throughput, economy of scale, and increased reliability.

Operating System Structure

• Multiprogramming is needed for efficiency, as a single user cannot keep the CPU and I/O devices busy at all times.
• Multiprogramming organizes jobs (code and data) so the CPU always has one to execute.
• A subset of total jobs in the system is kept in memory, and one job is selected and run via job scheduling.
• When a job has to wait, the OS switches to another job.
• Timesharing (multitasking) is a logical extension, where the CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing.

Operating-System Operations

• The operating system is interrupt-driven, responding to hardware interrupts, software errors, or user requests.
• Dual-mode operation allows the OS to protect itself and other system components, using a mode bit to distinguish between user and kernel mode.
• The operating system provides a timer to prevent infinite loops and process hogging of resources.

Process Management

• A process is a program in execution.

This quiz covers the concepts of multiprocessing in operating systems, including increased throughput, economy of scale, and increased reliability. It also discusses two types of multiprocessing: asymmetric and symmetric.