Memory Management Questions and Answers

Answer: D

Correct answer: the address generated by the CPU, before translation

A logical or virtual address is the one the CPU generates while a program runs. A physical address is what the memory unit finally sees. The memory management unit performs the translation between them at run time. The distinction is what makes modern operating systems possible. Each process has its own logical address space beginning at zero, and can neither name nor reach any address outside it, so isolation comes for free. Processes can be moved in physical memory without their addresses changing, which is what allows swapping, compaction and paging. The set of all logical addresses a process can generate is its logical address space; the corresponding physical addresses form its physical address space. The two are the same only when binding happens at compile or load time, which no general-purpose system now does. The user program never sees a physical address at all - it deals entirely in logical ones, and the mapping is invisible to it.

Answer: A

Correct answer: Power cord

Connectivity is what joins a device to the resources it needs, in the way a power cord joins it to the supply - the point of the comparison is that both are links rather than things in themselves. The internet is one thing you may connect to, and a floppy disk and data are not connections at all.

Answer: C

Correct answer: a free-frame list

The operating system maintains a free-frame list recording which physical frames are unallocated. When a page must be brought in, a frame is taken from that list; when a process terminates or a page is evicted, its frames are returned to it. If the list is empty, a victim page must be chosen by the replacement algorithm and evicted first - written back if it is dirty, discarded if clean. Real systems keep a reserve rather than letting the list run to zero, because finding a frame at the moment one is needed adds latency to a page fault. A background process reclaims pages when the free count falls below a threshold, so a frame is usually available immediately. The other options are all per-process or hardware structures with different jobs: a page table maps one process’s pages, the TLB caches recent translations, and the process control block holds a process’s saved state. None of them has any view of which physical frames are free system-wide.

Answer: B

Correct answer: Access point

Coaxial cable, fibre and shielded twisted pair are all cabling used in Ethernet. An access point belongs to a wireless network, which is a different medium.

Answer: D

Correct answer: The page table becomes large but internal fragmentation is low

A small page size reduces internal fragmentation, since the waste is on average half a page per process. But it multiplies the number of pages, so the page table grows - consuming memory and requiring more levels of indirection. It also reduces TLB coverage: each TLB entry maps less of the address space, so a given program touches more entries and the miss rate rises. And disk transfers become less efficient, because the fixed cost of a seek is amortised over less data. A large page size reverses all four: smaller table, better TLB coverage, more efficient transfers, but more internal fragmentation and more data transferred that may never be used. The compromise most systems have settled on is 4 KB, with support for huge pages of 2 MB or 1 GB where a database or a virtual machine host benefits from the reduced TLB pressure. Page size is always a power of two, so that splitting an address into page number and offset requires no arithmetic.

Answer: A

Correct answer: Computers can share information and share peripheral equipment

A LAN allows files and devices to be shared. It does not make any individual machine faster, and reaching the internet requires a further connection beyond the local network.

Answer: D

Correct answer: All of the above

A wide area network needs compatible equipment at each site, communication links of adequate bandwidth to span the distance, and processing capable of handling the traffic.

Answer: B

Correct answer: Google

Google is a search engine; Internet Explorer and Firefox are browsers, which are how a search engine is reached, and Flash was a plug-in for animation.

Answer: D

Correct answer: Switching hub

A switching hub, or switch, reads the destination address in each frame and forwards it only to the port where that address lies, instead of repeating it to every port as a plain hub does.

Answer: A

Correct answer: the page has been modified since it was loaded

The dirty or modify bit records whether a page has been written to since it was brought into memory. The hardware sets it on any write to the page. Its purpose is to avoid unnecessary disk writes. When a page is chosen for replacement, a clean page - one never modified - can simply be discarded, since an identical copy already exists on the backing store. A dirty page must be written out first. Since a disk write costs milliseconds, preferring clean victims measurably improves performance, and some replacement algorithms weigh the dirty bit alongside recency for exactly that reason. It sits among the other status bits in a page table entry: the valid bit, saying whether the page is resident; the reference bit, used by clock and second-chance algorithms to approximate LRU; and protection bits marking a page read-only or execute-only. Code pages are typically read-only and therefore always clean, which is one reason they are cheap to evict.