Device Management PDF

Device Management Angelika S. Balagot Instructor Basic Functions Monitoring the status of each device (storage drives, printers, etc.) Enforcing present policies - determine which process will get a device and for how long Allocating the devices Deallocating them a...

Device Management Angelika S. Balagot Instructor Basic Functions Monitoring the status of each device (storage drives, printers, etc.) Enforcing present policies - determine which process will get a device and for how long Allocating the devices Deallocating them at two levels - Process (task) level z - Job level Types of Devices Dedicated Devices Shared Devices z Virtual Devices Types of Devices Dedicated Devices - assigned to only one job at a time - serve that job for the entire time it’s active or until it releases them Examples: z - Tape drives - Printer - Scanner - Plotters Types of Devices Shared Devices - can be assigned to several processes Example: - Direct Access Storage Device z (DASD) - can be shared by several processes at the same time by interleaving their requests. Types of Devices Virtual Devices - a combination of dedicated and shared devices. - they’re dedicated devices that have been transformed into shared devices. Example: z - a printer converted into sharable devices through a spooling program - Spooling program reroutes all print requests to a disk Types of Devices Universal Serial Bus (USB) Controller - acts as an interface between the OS, device drivers, and applications attached via USB host. - One USB host can accommodate up to 127 different devices z - Devices can be flash memory, cameras, scanners, musical keyboards. - Each devices is identified by the USB host controller with a unique identification number, that allows many devices to exchange data with the computer using the same USB connection. Storage Media A physical device that receives, stores, and allows users and programs to access electronic data. The storage media might be inside a computer or other device or attached to a system externally, either directly or over a network. Example: z - CD ROM, DVD ROM, DAT tape, DLT tape, disk drives, SSD, Flash Drive, etc. Storage Media Storage media are divided into two groups: - Sequential Access Storage Media - store records sequentially, one after the other - Direct Access Storage Devices (DASD) - store either sequential or direct access files z There are vast differences in their speed and shareability. Sequential Access Storage Media Magnetic tape Developed for routine secondary storage in early computer systems and features records that are stored serially, one after other. The length of these records is usually z determined by the application program and each record can be identified by its position on the tape. To access a single record, the tape must be mounted and fast- forwarded until the desired position is located. Sequential Access Storage Media Magnetic tape Let’s consider a hypothetical computer system that uses a reel tape that is 2400 feet long. z Sequential Access Storage Media Density of the Tape Determined by the number of characters that can be recorded per inch, such as (1600 bpi). Bytes per inch (bpi) For example, if you had records z of 160 characters each, and were storing them on a tape with a density of 1600 bpi, then you can store 10 records on one inch of tape. Sequential Access Storage Media Records can be stored individually or grouped into blocks: If the records are stored individually, each record would need to be separated by a space to indicate its starting and ending places. If the records are stored in blocks - Preceded by a space - Followed by a space - Individual records are stored sequentially z within the block. Blocking - Way of grouping the record into blocks before recording them on tape. - The number of records in a block is determined by the application program. Sequential Access Storage Media Transfer Rate - The rate at which data is transferred from sequential access media - Density of the tape (measured in bpi), multiplied by tape drive speed (transport speed) z - Can be measured in inches per second (ips) Sequential Access Storage Media Transfer Rate - Transfer Rate (ips) = density * transport speed. Example: - Transport Speed is 200 z - Density is 1600 bpi - Transfer Rate = 1600 * 200 - Transfer Rate = 320,000 bytes can be transferred in one second. Sequential Access Storage Media How long does it take to access a block or record on magnetic tape? - depends on where the record is located, can be calculated. For example, our 2400-foot reel of tape with a tape transport speed of 200 ips can be read without stopping in approximately 2.5 minutes. Therefore, it would take 2.5 minutes zto access the last record on the tape. On the average, then, it would take 1.25 minutes to access a record. And to access one record after another sequentially would take as long as it takes to start and stop a tape - which is 0.003 seconds, or 3 milliseconds (ms). Sequential Access Storage Media Access Time - Total time required to access data in secondary storage. z End of Discussion Angelika S. Balagot Instructor