Input and output (IO) systems Last week we considered the memory management layer of the operating system. This week we will look at another layer of the operating system; the input output systems layer.

This week we are going to consider: – What is the IO system? – Device drivers – IO system and resource sharing – Daemons – Spooling – Direct Memory Access (DMA)

Input/Output (IO) System The IO system is concerned with how peripherals and system components ‘talk to’ each other. It often works together with other parts of the operating system Example: Deleting a file, user interface calls the IO system to operate the disk as well as the file system.

Device Drivers Every IO device needs a piece of software to allow the operating system and device to communicate. Sometimes the operating system can cope with particular device, without the need for extra software. Sometimes an extra piece of software is needed, this is a device driver.

Sometimes device drivers are considered to be part of the IO system; even if they are software that was added later. Device driver perform same action as the basic IO functions, but just for one device. IO system is sometimes thought of as a set of basic device drivers.

Unix has all the hardware device driver built-in. Windows is able to add or delete device drivers as needed.

Resource Sharing What the resource is determines how it is shared. A printer for example, a process using a printer would have solo control, until it has finished printing, otherwise two (or more) printing jobs would be trying to use the printer at the same time.

Daemons Unix uses programs daemons, to organise requests for data transfer between a device and multiple users. The device request in placed in a list of other requests (queue) until the current request has been dealt with.

Spooling Spooling (Simultaneous Peripheral Output Online) is system that stores peripheral requests in a queue, until dealt with. A Spooler is traditionally a term reserved for a spooler for a printer.

Spoolers are for output only, general in large volumes. Device drivers are generally used for devices such as Hard disks, CD drives. Though we do usually refer to the software on PCs for communicating with printers as printer drivers.

Direct Memory Access (DMA) Sometimes devices need data to be transferred between the processor and the device as fast as possible. Examples: – Network cards – Scanners – Hard disks

To handle the fast devices, the PC uses Direct Memory Access. An extra device on the motherboard handles this, transferring the data quickly and leaving the processor to get on with other tasks. Throughput is increased.

IO systems role in DMA is to organise and negotiate details such as: – The memory locations to access – Whether data is to written or read – Which DMA line (channel) is to be used.

Summary The IO system is concerned with how peripherals and system components ‘talk to’ each other. Every IO device needs software to allow the operating system and device to communicate. The operating system often copes with particular device, without the need for extra software. Sometimes an extra piece of software is needed, this is a device driver. What the resource is determines how it is shared.

Unix uses programs daemons, to organise requests for data transfer between a device and multiple users. The request in placed in a queue until the current request has been dealt with. Spooling is system that stores peripheral requests in a queue, until dealt with. A Spooler is a term reserved for a spooler for a printer. Spoolers are for output only, general in large volumes. Device drivers are generally used for devices such as Hard disks, CD drives

To handle the fast devices, the PC uses Direct Memory Access. An extra device on the motherboard handles this, transferring the data quickly and leaving the processor to get on with other tasks. IO systems role in DMA is to organise and negotiate details with the other parts of the operating system.