Correct Answer: For load-time dynamic linking: Load module to be loaded is read into memory Any reference to a target external module causes that module to be loaded and the references are updated to a relative address from the start base address of the application module With run-time dynamic loading: Some of the linking is postponed until actual reference during execution Then the correct module is loaded and linked
2. In the context of memory management, what are placement and replacement algorithms?
Correct Answer: Placement algorithms determine where in available real-memory to load a program Common methods are first-fit, next-fit, best-fit Replacement algorithms are used when memory is full, and one process (or part of a process) needs to be swapped out to accommodate a new program The replacement algorithm determines which are the partitions to be swapped out
Correct Answer: We encounter cycle stealing in the context of Direct Memory Access (DMA) Either the DMA controller can use the data bus when the CPU does not need it, or it may force the CPU to temporarily suspend operation The latter technique is called cycle stealing Note that cycle stealing can be done only at specific break points in an instruction cycle
4. What is the resident set and working set of a process?
Correct Answer: Resident set is that portion of the process image that is actually in real-memory at a particular instant Working set is that subset of resident set that is actually needed for execution (Relate this to the variable-window size method for swapping techniques)
5. What is the Translation Lookaside Buffer (TLB)?
Correct Answer: In a cached system, the base addresses of the last few referenced pages is maintained in registers called the TLB that aids in faster lookup TLB contains those page-table entries that have been most recently used Normally, each virtual memory reference causes 2 physical memory accesses- one to fetch appropriate page-table entry, and one to fetch the desired data Using TLB in-between, this is reduced to just one physical memory access in cases of TLB-hit
Correct Answer: Windows NT uses protection mechanism called rings provides by the process to implement separation between the user mode and kernel mode