Operating System Fundamentals
Figure 5.4 Device Driver Structure
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| Figure 5.4 Device Driver Structure In this diagram, the blue box represents the device driver, which is divided into the Upper Half and Lower Half. The red arrows represent the flow of instructions from the operating system, which first pass into the Upper Half, then into the Shared Request List. These instructions are then programmed by the Lower Half, and forwarded to the device controller for execution. The blue arrows represent the flow of requests and data out of the device driver. In this diagram, the device controller is returning results back to the device driver, which then sends them back out to the operating system. The interrupt handler is also demonstrated issuing an interrupt request to the interrupt controller. Operating System Fundamentals 70 Managing Magnetic Disks Magnetic disk storage represents one of the most popular categories of IO resources used by a computer. Processes and threads must be able to read data from, and write data to magnetic storage devices such as hard disks and floppy disks. This is most frequently done when accessing pages from virtual memory, but it also occurs when processes try to open or close files stored on disks. In this section, we will look at how magnetic storage devices are formatted to hold data, and how that data is structured on a disk so that the operating system can read and manage it. We will also take a look at the elevator algorithm, which is a pattern used by operating systems to manage data retrieval as efficiently as possible. Disk Formatting Disk formatting is the process of preparing a disk to hold data. When you reformat a disk, it destroys all of the data previously stored on it. There are three key stages to the formatting process fora disk Low-level formatting Takes place at the factory. Involves physically drawing tracks and sectors on the disk surface. Partitioning Done by the user. Involves dividing the disk into logical sections. Only primary hard disks can be partitioned (cannot partition external hard disks or floppy disks) High-level formatting Done by the user. Involves the selection of a file system (such as FAT or NTFS for Windows, and the installation of an operating system. Different partitions can use different file systems, and can even be used to install different operating systems in the same computer. Download 2.34 Mb. Share with your friends:
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