![]() Each controller card ( device ) on a system has a different set of addresses ( registers, a.k.a. I/O Control consists of device drivers, special software programs ( often written in assembly ) which communicate with the devices by reading and writing special codes directly to and from memory addresses corresponding to the controller card's registers.Modern disk put more and more of the electronic controls directly on the disk drive itself, leaving relatively little work for the disk controller card to perform. At the lowest layer are the physical devices, consisting of the magnetic media, motors & controls, and the electronics connected to them and controlling them.File systems organize storage on disk drives, and can be viewed as a layered design:.Block sizes may range from 512 bytes to 4K or larger. Disks are usually accessed in physical blocks, rather than a byte at a time.Hard disks have two important properties that make them suitable for secondary storage of files in file systems: (1) Blocks of data can be rewritten in place, and (2) they are direct access, allowing any block of data to be accessed with only ( relatively ) minor movements of the disk heads and rotational latency.Abraham Silberschatz, Greg Gagne, and Peter Baer Galvin, "Operating System Concepts, Ninth Edition ", Chapter 12 12.1 File-System Structure.Operating Systems: File-System Implementation ![]()
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