WGU C191 MODULE 3 Latest Update Graded A Magnetic disks ✔✔What is the most common secondary storage? Transfer rate ✔✔The rate at which data flow between drive and computer Positioning time (random -access time) ✔✔Time to move disk arm to desired cylinder (seek time) and time for desired sector to rotate under the disk head (rotational latency) Head crash ✔✔Results f rom disk head making contact with the disk surface (it's bad) EIDE, ATA, SATA, USB, Fiber Channel, SCSI, SAS, Firewire ✔✔What are examples of I/O busses? Host controller ✔✔Uses bus to talk to disk controller built into drive or storage array Seek dist ance ✔✔Seek time is equal to what? Bandwidth ✔✔Is the total number of bytes transferred, divided by the total time between the first request for service and the completion of the last transfer Shortest seek time first, is a form of SJF but may cause st arvation of some requests. ✔✔SSTF Storage area networks (SANs) ✔✔Network in which many hosts attach to many storage units Network -attached storage (NAS) ✔✔A storage made available over a network rather than over a local connection (such as a bus) Demand paging ✔✔Bring a page into memory only when it is needed Less I/O needed Less memory needed Faster response More users ✔✔What are 4 benefits of demand paging? Execution time binding ✔✔The method of binding instructions and data to memory performed by most general -purpose operating systems. Logical address ✔✔An address generated by the CPU, also called virtual address Physical address ✔✔An address l oaded into the memory -address register of the memory from the MMU. Memory management unit (MMU) ✔✔- The hardware device that maps from virtual to physical addresses dynamically (hardware device) - user program deals with logical addresses; it never sees real physical address - the value in the relocation register is added to every address generated by a user process at the time it is sent to memory Virtual address ✔✔What is another name for logical address? dynamic loading ✔✔- routine is not loaded un til it is called - unused routine never loaded - useful when large amounts of code needed dynamic linking ✔✔- linking postponed until execution time - stub is used to locate library routine - stub replaces itself with address of the routine and then executes the routine -dynamic linking useful for libraries -system known as shared libraries swapping ✔✔A process can be swapped temporarily out of memory to a backing store, and then brought ba ck into memory for continued execution - Major part of swap time is transfer time; total transfer time is directly proportional to the amount of memory swapped - System maintains a ready queue of ready -to-run processes which have memory images on disk backing store ✔✔fast disk large enough to accommodate copies of all memory images for all users; must provide direct access to these memory images Roll out, roll in ✔✔swapping variant used for priority -based scheduling algorithms; lower -
priority process is swapped out so higher -priority process can be loaded and executed Contiguous Allocation ✔✔main memory usually into two partitions - resident operating system usually held in low memory with interrupt vector - user processes then held in high memory relocation registers ✔✔- used to protect user processes from each other, and from changing operating -system code and data - base register and limit register Base register ✔✔Memory register that holds the smallest, legal physical -memory address Limit regi ster ✔✔Memory register that specifies the size of the range
priority process is swapped out so higher -priority process can be loaded and executed Contiguous Allocation ✔✔main memory usually into two partitions - resident operating system usually held in low memory with interrupt vector - user processes then held in high memory relocation registers ✔✔- used to protect user processes from each other, and from changing operating -system code and data - base register and limit register Base register ✔✔Memory register that holds the smallest, legal physical -memory address Limit regi ster ✔✔Memory register that specifies the size of the range
