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Input Output Functions of an Operating System

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Ricki Lambert Operating Systems Assignment 2 Input Output Subsystem Introduction An operating system is the device used to communicate with all input and output devices. For example this may be a keyboard or mouse, things of this nature. This process is controlled by a virtual layer which is known as a application input output interface. It is this device that ensures every input output device under goes a buffering and scheduling process. From here the operating system can communicate with the processor in order for the hardware device to be controlled / managed. There are four main functions that assist with this processor communications and they are as follows; 1. Input output instructions vs. memory mapped. - This is where information is sent in order for the process to be logged in to its own memory location within a register. 2. Input output hardware device - At this stage the operating system will check whether it has to read the device or write to it. 3. Polled vs. interrupt driven - Modern operating systems use interrupt driven methods in preference to its counterpart. ...read more.


be issued in to the status register * The device can see the command is ready and from here is sets the device to busy * It is now enabled to perform the writing operation It is when the above is complete that the cycle can begin again for a new set of instructions. More complex processors use the interrupt driven method and are capable of the following tasks; * At the end of each instruction it checks for further interrupts that maybe pending * It will save the programme counter * Saves the processor status * It can change the processors mode * It will jump to the well known address Interrupt Driven I/O - Data is entered form a keyboard and stored in the memory so the instruction is to write. This is then placed in to the instruction register but the actual data itself will be placed in the data register. The CPU will then receive this and send the data from the register to its desired destination. The instructions are stored in to the intermediate buffer. ...read more.


They are single buffering, double buffering and circular buffering. A singular buffer is used store data between the input and output device and user process. There is a double buffer which has twice the holding capacity and a circle buffer which holds many more commands. This allows less CPU waiting which ensures a better and more efficient system. This form of CPU management can then be broken down into input output issues. Caching: Caching is the form of fast memory holding copied of data (normally the data held in the data buffer). It can work with both read and write and it is key to input output performance. Scheduling: Operating systems try to invoke fairness when switching between input and output properties. This is similar to the scheduling technique. Spooling: Spooling is the form of control used by singular input/output devices. It can queue commands for example a printer, by storing them in the spooling area. Error Handling: It has input output error checking properties; it can recover from a disk read error, when the device is unavailable and such possibilities. The system often records errors in a log on the operating system. Device Reservation: It can use system calls for specific duties when needing exclusive access to a device. ...read more.

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