Operating System Concepts - Multiprocessing

Study Notes

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.

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.

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.

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.

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.

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.

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.

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 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.

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.

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.

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.