Regarding virtual memory management techniques, specifically Thrashing, Working-Set Model, Page Replacement Algorithms, and Copy-on-Write (COW), which of the following statements are TRUE?
A (a) A classic symptom of thrashing is low CPU utilization. This occurs because processes spend the majority of their time waiting for the paging device (I/O), which often misleads the standard OS scheduler into increasing the degree of multiprogramming, thereby worsening the thrashing.
B (b) Belady's anomaly refers to the phenomenon where increasing the number of available page frames results in an increase in the number of page faults. This anomaly can occur in the FIFO algorithm but is mathematically proven to be impossible in LRU (Least Recently Used), which belongs to the class of stack algorithms.
C (c) When fork() is executed with Copy-on-Write enabled, the parent and child processes share the same physical pages. To detect when a copy is needed, these shared pages are initially marked as read-write in the page table so that the hardware allows the write to proceed immediately without OS intervention.
D (d) The Working-Set Model prevents thrashing by estimating the current locality of each process. If the sum of the working-set sizes of all active processes exceeds the total number of available frames, the operating system selects a process to suspend (swap out) to release frames.
