Operating System Structure Questions and Answers

Answer: D

All four are Windows handles: (1), (2), (3) and (4).

In the Windows API a handle is an opaque value that identifies an object managed by the system. HDC is a handle to a device context, HBRUSH to a GDI brush, HMENU to a menu and HWND to a window. All four are handle types defined in the Windows headers.

Any option that leaves out HBRUSH or HMENU (options A, B and C) is incomplete.

Answer: D

Terminal Services support multiple interactive user sessions on a single system.

Windows Terminal Services, renamed Remote Desktop Services in Windows Server 2008 R2, lets several users log on to the same Windows server at once, each in an independent session with its own desktop and applications, usually over the Remote Desktop Protocol from another computer.

The name refers to terminals (client machines), not to terminating anything, so ending sessions and shutting down are wrong. Managing display devices is the job of device drivers and display settings.

Answer: A

The diagram represents a Centralized system.

All the processing is done by one computer system, C, and the dumb terminals, T, have no processing power of their own. They only send keystrokes to the central computer and display what it returns. A single computer serving many terminals is the classic centralized (time-sharing mainframe) arrangement.

A distributed system would need several computers, each with its own processing, cooperating over a network. Local-access and remote-access describe how a user reaches a computer, not the architecture shown, in which everything depends on the one central system.

Answer: B

The kill command is used to Send a signal to a process.

Despite its name, kill sends any signal to a process: by default SIGTERM, asking it to terminate, but also SIGKILL, SIGSTOP, SIGCONT, SIGHUP and others, for example kill -HUP 1234 to make a daemon reload its configuration.

Terminating a process is only one common use, which is why 'Kill a running process' is less appropriate. Ending a login session or shutting the system down is done with other commands.

Answer: B

Windows uses a Hybrid kernel and Linux a Monolithic kernel.

The Windows NT kernel combines microkernel ideas (a small executive, subsystems and message passing) with many services running in kernel mode for speed, so it is classed as hybrid. Linux runs the whole kernel, including drivers, file systems and networking, in a single kernel address space, which is the monolithic design, extended with loadable modules.

Linux is not a microkernel (Linus Torvalds famously debated that with Andrew Tanenbaum), so options pairing it with 'Micro' are wrong, and Windows is not purely monolithic.

Answer: D

The availability is approximately 99.97%.

Availability is the fraction of time the system is up:

\[ \begin{aligned} A &= \frac{MTBF}{MTBF + MTTR} \\ &= \frac{43200}{43200 + 10} \\ &= 0.99977 \approx 99.97\% \end{aligned} \]

Here 30 days = 30 × 24 × 60 = 43,200 minutes, so both times are in minutes. The other options are far too low: 96.97% would mean about 22 hours of downtime a month, not 10 minutes.

Answer: A

An example of a distributed OS is Amoeba.

Amoeba, developed by Andrew Tanenbaum and colleagues at the Vrije Universiteit Amsterdam, makes a collection of networked machines appear to users as a single time-sharing system, with processes and files spread transparently across them.

UNIX and MULTICS are time-sharing operating systems for a single computer, and MS-DOS is a single-user, single-tasking system.

Answer: B

A network operating system runs on the server, option (B).

A network operating system (NOS) is the software on the central server that manages the shared resources of a network: users and groups, file and printer sharing, security and administration. The client machines run their own ordinary operating system plus client software to reach the server.

Option A and option C would put the NOS itself on every machine, which is the distributed operating system or the peer-to-peer arrangement rather than the client-server NOS the question describes. Option D is wrong because the NOS must run somewhere, and that place is the server.

Answer: C

The command makes the variable available to child processes.

VAR=10 creates a shell variable that exists only in the current shell. export VAR then marks it for the environment, so every program or subshell started from this shell afterwards receives a copy of VAR with the value 10. A script run from the shell can read it, for example with echo $VAR.

Option A describes VAR=10 on its own, before the export. A read-only variable is made with the readonly command, and a variable is deleted with unset; export does neither.

Answer: B

The keyed answer is that it prints the name of the shell executing the script.

$0 is the shell's special parameter for the name of the program that is running. In an interactive shell, echo $0 prints the shell's own name, such as bash. Strictly, inside a script it holds the name by which the script was invoked, for example ./backup.sh; the options do not offer that, and the paper's option B is its description of $0 as the name of the running program.

The other options belong to other parameters and commands. The last exit status is $?. The current working directory is printed by pwd. The first argument to a script is $1, a common mix-up with $0.