Chapter 6 review. Are the following statements true or false? Explain why or why not.

a) An operating system is a virtual machine.
True. It's a virtual machine that lets a user accomplish tasks that would be difficult and time-consuming to perform directly with the underlying actual machine.

b) An operating system is a resource manager.
True. It's also a collection of programs that manage the resources, including the processors, memory, and input/output devices of a computer.

c) Job control language (JCL) described the employment of computer programmers.
False. JCL encoded specific instructions to a batch operating system or its human operator.

d) Batch operating systems streamlined usage of computer resources.
True. Rather than wait for people to submit jobs, a batch OS keeps itself busy by taking jobs (programs to run) from a job queue.

e) Multiprogramming makes both multi-user and multi-tasking systems possible.
True. Multiprogramming lets a system switch between several different processes all stored in memory. These processes may serve many users (multi-user) and/or accomplish different tasks (multi-tasking).

f) Multitasking is when several users can send tasks to the same machine.
False. Multitasking lets a single user submit and switch between many tasks or programs.

g) Preemptive multitasking is when users determine which task is using the processor.
False. Preemptive multitasking means the OS can determine when to switch. Cooperative multitasking relies more on users as well as programs that permit the OS to switch them out of execution.

h) In a LAN, a client is a person who is requesting services.
False. A client is a computer that requests services from other machines, called servers.

i) Access to the Internet typically requires access to a network server.
True. This server is often called an Internet Service Provider (ISP). Access to a server may be via modem or a high-speed connection such as Ethernet.

j) Booting a system is giving a recalcitrant machine a swift kick.
False. Machines don't respond well to violence. Booting is the process a machine and its operating system go through to start up.

k) To enable a PC to run Unix instead of DOS, you must reprogram the ROM.
False. The same ROM can start up many different operating systems.

l) The scheduler responds to events--such as when a user clicks on a mouse.
False. The command processor responds to events. The scheduler arranges for the execution of a program, by adding it to a job queue or process table.

m) A program counter is similar to the program address register, only every process has one.
True. The difference is that the PAR is built-into the hardware, whereas the operating system maintains a copy of a PC for each process in the process table.

n) Virtual memory is limited by the amount of RAM a machine has.
False. Virtual memory usually far exceeds RAM, by using space on a hard disk in a "swap file."

o) A dispatcher responds to interrupts by switching from one process to another.
True. The dispatcher saves the state of one process (its registers and PC) and sets up the PC and registers for the new program, as the current process.

p) Thrashing is when a frustrated user is shaking a keyboard or a mouse.
False. It's when an OS spends most of its time switching between processes rather than executing them.

q) A spool can make more effective use of high quality printers and other resources.
True. Spooling--holding data for output on disk until the device is ready--lets each process act as if it has use of its own printer (actually, it's a virtual printer), thus avoiding any collisions.

r) A fully connected network has a higher connection cost than a ring or hierarchical network.
False. A fully connected network guarantees immediate links from any node to any other node. The problem is that the physical cost of a fully connected network quickly becomes prohibitive.

s) Only hosts, which are servers for other machines, require their own unique host name.
False. If a node machine on a network is to be identifiable to other machines on the Internet, it must have its own unique host name. So a client machine may need its own host id. But it's also possible for a clients not to be identifiable except to an Internet Service Provider.

t) A domain name service (DNS) provides names for users on the Internet.
False. The primary job of a DNS is to map symbolic host names into numeric Internet addresses.

u) HTTP, FTP, NSP, SNMP and TCP are examples of network protocols.
True. HTTP is Hypertext Transfer Protocol, used by most WWW documents. FTP is File Transfer Protocol, a generic way to transfer files. NSP is the Name Server Protocol for binding host names to Internet addresses. SNMP is the Simple Network Management Protocol, which establishes communication with between two machines through a network. TCP is the Transmission Control Protocol, which breaks files up into packets, each one with a TCP header on it providing information about how to put the packets back together again on the other side.

v) Computer security has to do with keeping unauthorized users out of a computer room.
False. Computer security measures confidence in the protection of a system and its data.

w) Protection and security are more important for networked than stand-alone computers.
True. The more users and processes involved, the more potential for damage or tampering.

x) Obscure words like 'ROM' or 'cipher' or 'gnostic' make good passwords.
False. Words are fairly easy to guess, using a large dictionary. Good passwords contain at least one non-alphabetic character, so that they are not words at all.

y) A public-key encryption scheme is unsuitable for securing data over the Internet.
False. Though you make your public key available to anyone, your decryption key is private.
By using fairly large (several hundred digits long) prime numbers as decryption keys, breaking this scheme, while conceivable, is not feasible in a reasonable time frame.

z) Viruses and other malicious software and spread via floppy diskettes or over networks.
True. Unwittingly, you can spread a virus which attaches to your floppy and then copies itself to the next machine in which you insert the diskette. Viruses have also been known to spread through e-mail.