Chapter 5: input/output (IO) Management

Chapter 5: input/output (IO) Management

I/O device concept:

It refers to all devices inside the computer except the central processor and memory, also known as external devices.

I/O device category:

· Classification by interaction object:

· Human-Computer Interaction Device

· Devices that interact with computers or other electronic devices

· Same-Email devices between computers

· Classification by interaction:

· Input (readable)

· Output (writable)

· Input/output (read/write)

· Classification by peripheral features:

· Features

· Data transfer rate

· Information Organization Features

I/O Control Mode:

· Program Access Control Method

· Interrupt control mode

· DMA (Direct Memory addressing): Data Transfer in memory

· Channel mode (represented by USB)

I/O software goals:

· Device independence: when accessing a device, you do not need to know the specific operation method of the device.

· Uniform Naming

I/O hierarchy:

· User layer

· Device independent Layer

· Device driver layer

· Medium fault

· Hardware layer

I/O scheduling concept:

Scheduling a group of requests is to determine a good order to run these requests.

The operating system maintains a request pair column for each device for scheduling.

One way for the I/O core subsystem to improve computer efficiency is to schedule I/O operations and use memory or disk storage technology, such as buffering, high-speed cache, and off-line.

Cache:

High-speed cache is a high-speed memory that can retain data copies. The cache copy access is more efficient than the original data access.

Cache zone:

A buffer is the memory area used to store data between two devices or between devices and applications.

Three Functions of buffering are used:

· The speed difference between producers and consumers who process data streams

· Coordinating devices with inconsistent data sizes

· Copy semantics of application I/O

Buffer zone:

· Single Buffer

· Dual Buffering

· Circular buffer

· Buffer Pool

Device allocation Overview:

· For an exclusive device process, you must apply for allocation before I/O transmission.

· For shared devices and Virtual Devices, there is no need to consider allocation issues. The process can be directly requested through file systems.

Principles of device allocation:

Depends on the device features, user requirements, and system configurations.

Device allocation methods: Static and Dynamic Allocation

Device allocation policy: first request first allocation (FIFO), first allocation of higher priority

SPOOLing ):

Convert an exclusive device into a shared Device

Composition of the SPOOLing system:

· Input and Output wells (stored in external storage)

· Input buffer and output buffer (in memory)

· Input process SP1 and output process SP0

Error handling:

If an error occurs on the I/O device, it should be handled by I/O.