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The Computer Network Center (CNC) is a division of the Purdue School of Engineering and Technology at IUPUI. The CNC provides all academic research computing support, as well as Web design and Web application development for engineering and technology students, staff, and faculty. This support includes Web and multimedia services, as well as specialized support for engineering research labs.

For more information about the services that the CNC offers, point your browser to the following URL:

CISC and RISC (Complex and Reduced Instruction Set Computer, respectively) are dominant processor architecture paradigms. Computers of the two types are differentiated by the nature of the data processing instruction sets interpreted by their central processing units (CPUs). They both have advantages and drawbacks, which are detailed below.

To improve performance, CISC systems try to reduce the number of instructions programs must call. To do this, they have large sets of microcode instructions that cover a broad range of tasks. A single microcode instruction, in turn, when translated in the CPU, may become several tasks the processor performs. As a consequence, instructions are of variable length and often require more than one clock cycle to complete.

RISC systems, on the other hand, seek to improve performance by reducing the number of clock cycles required to perform tasks. They have small sets of simplified instructions, doing away with microcodes altogether in most cases. While this means that tasks require more instructions, instructions are all of the same length and usually require only one clock cycle to complete. Because of this, RISC systems are capable of processing instructions in parallel in a process called pipelining. The CPU works on more than one instruction at once by starting the second instruction before it completes the first one. This greatly increases throughput and makes RISC systems substantially faster than their CISC counterparts. RISC systems do have a few disadvantages, however. Notably, because programs usually have more instructions, compilers and applications written in assembly language are more difficult to build for RISC systems.

Examples of CISC processors include the 680x0, x86, and the VAX. RISC processors include the PowerPC, MIPS, SPARC, and the Alpha. Intel's Pentium series chips are sometimes described as CRISC (Complex Reduced Instructions Set Computer) processors, because they are hybrids of the two architectures.

For more information about RISC and CISC, read Apple Computer's "Introduction to RISC Technology," which is available from a number of sites, including:

COM (Component Object Model) is Microsoft's component software architecture developed primarily for Windows. It is the foundation upon which OLE and ActiveX are based, and provides a means to re-use code without requiring re-compilation. In COM, a component is a platform-specific binary file that compliant applications and other components can utilize. Programs incorporating a component's services never have access to its internal data structure, but instead include pointers to its standardized interface. Thus, it is possible for components to interact with each other regardless of how they work or what language they are written in.

COM+ is an enhanced version of COM that provides better security and improved performance. DCOM (Distributed Component Object Model) is an extension of COM that allows applications and components to communicate with each other over a network.

For more detailed information about COM, COM+, DCOM, and related technologies, visit:

Compressed or archived files may contain many separate files in one large archive. Before you can read or run all the separate files and programs, you must use an archiving program to extract the files from the archive.

Many good shareware and freeware programs exist that have this ability. The best archivers allow you to do such things as look at the compressed files before extraction, select which files you want to extract, and allow drag-and-drop operations. They might also support a large variety of different archive file types, such as tar and GNU Zip (Unix), Zip (Windows), and StuffIt (Mac OS). To allow transfer of binary files by e-mail, some archivers have various coding schemes, such as uuencoding, built in.

You can find archive programs at most FTP sites and on the World Wide Web at many shareware sites. For more information, see the references at the end of this article.

Note: You cannot download archived files using an ASCII file transfer. If you are transferring these files using a regular modem connection, you must use a protocol such as xmodem, ymodem, or zmodem. If you are transferring an archived file by FTP, be sure to first set your file transfer type to binary. To do this, at the FTP prompt, enter:

What are computer viruses, worms, and Trojan horses?

What is a virus?

A computer virus, according to Webster's Collegiate Dictionary, is "a computer program usually hidden within another seemingly innocuous program that produces copies of itself and inserts them into other programs or files, and that usually performs a malicious action (such as destroying data)". Two categories of viruses, macro viruses and worms, are especially common today. Computer viruses are never naturally occurring; they are always man-made. Once created and released, however, their spread is not directly under human control. One example of a virus is the Anna Kournikova virus, which comes in the form of a picture sent through e-mail.

Macro viruses

A macro is a piece of code that can be embedded in a data file. Some word processors (e.g., Microsoft Word) and spreadsheet programs (e.g., Microsoft Excel) allow you to attach macros to the documents they create. In this way, documents can control and customize the behavior of the programs that created them, or even extend the capabilities of the program. For example, a macro attached to a Microsoft Word document might be executed every time you save the document and cause its text to be run through an external spell checking program.

A macro virus is a virus that exists as a macro attached to a data file. In most respects, macro viruses are like all other viruses. The main difference is that they are attached to data files (i.e., documents) rather than executable programs. Many people do not think that viruses can reside on simple document files, but any application which supports document-bound macros that automatically execute is a potential haven for macro viruses. By the end of the last century, documents became more widely shared than diskettes, and document-based viruses were more prevalent than any other type of virus. It seems highly likely that this will be a continuing trend. One example of a macro virus is the Melissa virus. It is delivered via e-mail as a Word document attachment with the filename


			List.doc

Worms

Worms are very similar to viruses in that they are computer programs that replicate functional copies of themselves (usually to other computer systems via network connections) and often, but not always, contain some functionality that will interfere with the normal use of a computer or a program. The difference is that unlike viruses, worms exist as separate entities; they do not attach themselves to other files or programs. Because of their similarity to viruses, worms are often also referred to as viruses. A well-known example of a worm is the ILOVEYOU worm, which invaded millions of computers through e-mail in 2000.

What is a Trojan horse?

Named after the wooden horse the Greeks used to infiltrate Troy, a Trojan horse is a program that does something undocumented which the the programmer intended, but that the user would not approve of if he or she knew about it. According to some people, a virus is a particular case of a Trojan horse, namely one which is able to spread to other programs (i.e., it turns them into Trojans too). According to others, a virus that does not do any deliberate damage (other than merely replicating) is not a Trojan. Finally, despite the definitions, many people use the term "Trojan" to refer only to a non-replicating malicious program. An example of a Trojan horse is W32.DIDer. This virus has been found on the computers of users who have downloaded the popular file-sharing program Grokster.

Also see:

Note: On most systems, you must get permission from the system administrator before you can submit job requests to cron. On many shared systems, because there is only one crontab file, only the administrator has access to the crontab command. The cron and crontab commands are not available on any of the Indiana University central systems (such as the Shakespeare systems or Steel).

The cron daemon is a long-running process that executes commands at specific dates and times. You can use this to schedule activities, either as one-time events or as recurring tasks.

For commands that need to be executed repeatedly (e.g., hourly, daily, or weekly), you can use the crontab command. The crontab command creates a crontab file containing commands and instructions for the cron daemon to execute. You can use the crontab command with the following options:

crontab -a filename	Install filename as your crontab file. On many systems, this command is executed simply as crontab filename (i.e., without the -a option).
crontab -e	Edit your crontab file, or create one if it doesn't already exist.
crontab -l	Display your crontab file.
crontab -r	Remove your crontab file.
crontab -v	Display the last time you edited your crontab file. (This option is only available on a few systems.)
crontab -u user	Used in conjunction with other options, this option allows you to modify or view the crontab file of user. When available, only administrators can use this option.

Each entry in a crontab file consists of six fields, specifying in the following order:

The fields are separated by spaces or tabs. The first five are integer patterns and the sixth is the command to execute. The following table briefly describes each of the fields:

Field	Value	Description
minute	0-59	The exact minute that the command sequence executes
hour	0-23	The hour of the day that the command sequence executes
day	1-31	The day of the month that the command sequence executes
month	1-12	The month of the year that the command sequence executes
weekday	0-6	The day of the week that the command sequence executes (Sunday = 0, Monday = 1, Tuesday = 2, and so forth)
command	Special	The complete sequence of commands to execute. The command string must conform to Bourne shell syntax. Commands, executables (such as scripts), or combinations are acceptable.

Each of the patterns from the first five fields may be either * (an asterisk), meaning all legal values, or a list of elements separated by commas. An element is either a number or an inclusive range, indicated by two numbers separated by a minus sign (e.g., 10-12). You can specify days with two fields: day of the month and day of the week. If you specify both of them as a list of elements, cron will observe both of them, for example:

The cron daemon would run the program myprogram in the mydir directory on the first and fifteenth of each month, as well as on every Monday. To specify days by only one field, the other field should be set to * , for example:

If a cron job specified in your crontab entry produces any error messages when it runs, you will get a mail message reporting the errors.

Computers use an internal clock to synchronize all of their calculations. The clock insures that the various circuits inside a computer work together at the same time.

The speed of a clock is measured by how many ticks per second the clock makes. This unit of measurement is called a Hertz (Hz). One Hertz equals one tick per second. The clock speed of computers is usually measured in Megahertz (MHz). One Megahertz equals one million ticks per second.

Clock speed can be used as a rough measurement of how fast a computer is. A 166MHz computer will be faster than a 120MHz computer with the same processor and the same amount of memory. However, clock speed cannot be used to compare computers with different types of processors or computers with different amounts of memory.

Originally, the term "hacker" described any amateur computer programmer who discovered ways to make software run more efficiently. In a broader sense, the term "hacker" describes anyone who writes computer programs, modifies computer hardware, or tinkers with computers or electronic devices for fun. Hackers will "hack" on a problem until they find a solution, always trying to make their equipment work in new, more efficient ways.

Recently, the popular definition of "hacker" has changed to describe a person who maliciously breaks into computer networks with the intent to snoop, steal data, or tamper with files.

Legitimate hackers resent the association of the term "hacker" with criminal activity. They use the term "cracker" to describe someone who breaks into networks.

The term "multi-spin" refers to the way in which a CD-ROM drive spins a CD-ROM to access data. When the drive reads data from the CD-ROM, the CD spins at a rate that depends on the location of the laser. For the drive to read data from the CD at a constant rate, the drive motor must slow down or speed up. If the laser is close to the inner tracks of the disk, the CD spins much faster. If the laser is reading from the outer tracks, it spins much more slowly.

The drive must spin the disk faster because the circumference at the edge of the CD-ROM is greater than at the center, and because the data on a CD-ROM are written at the same linear density everywhere on the disk. The CD's rotation speed must be slower to compensate for the larger circumference in order to read data at the same rate as at the smaller circumference.

This method of spinning at different rates is called Constant Linear Velocity (CLV). Many CD-ROM drives, especially older drives, employ this technology. Many newer drives, however, employ a technology called Constant Angular Velocity (CAV). With CAV, the disk rotates at a constant speed regardless of what area of the disk is being accessed. The reported speeds of CAV drives can be misleading because they refer to the access speeds of the outer tracks. For more information, see the Knowledge Base document What is meant by the speed of a CD-ROM drive?

The Common Gateway Interface (CGI) is a method of allowing a hyperlink to refer to a program rather than a static Web page. The easiest way to understand how a CGI works is by contrast with an ordinary Web page.

When you use a browser to link to a URL, the browser requests that the host named in the URL send the data specified by the rest of the URL. This is normally just the contents of the file or directory specified by the URL, encoded with the appropriate MIME type.

However, if the URL points to a CGI, the computer on the far end runs the program, and sends its output to the client as though the output were the contents of an HTML file. Depending on the URL, you might not be able to tell that a CGI ever ran.

CGIs are often used for processing submissions from HTML forms (collections of fill-in fields, checkboxes, buttons, etc.). They can also generate variable or customized content for a Web page, ranging from visitor counters to data based upon information supplied by the client browser.

You can write a CGI program in any programming language supported on the server computer. You can find many tutorials on the Web to help you write a CGI. The following two are a good start:

In addition, a number of excellent packages have been written that make it easier to program CGIs in Perl or C. There is a huge collection of resources about CGI, HTML, forms, and all aspects of the Web and the Internet, on the University of Geneva's TECFA Toolbox page at:

CMOS, short for Complementary Metal Oxide Semiconductor, is a low-power, low-heat semiconductor technology used in contemporary microchips, especially useful for battery-powered devices. The specific technology is explained in detail at:

Most commonly, though, the term CMOS is used to refer to small battery-powered configuration chips on system boards of personal computers, where the BIOS stores the date, time, and system configuration details.

Note: UITS is replacing Cord accounts for IUPUI students, faculty, and staff with accounts on Steel, an interactive environment for general purpose Unix computing, which is also the location for editing personal Web pages served by Php. After August 18, 2002, UITS will not create new Cord accounts. On December 23, 2002, UITS will retire Cord. For information on how to create a Steel account, see the Knowledge Base document What is Steel? For information on how to copy files from your Cord account to your Steel account, see the Knowledge Base document On a PC or Mac, how do I move files from my Cord account to my Steel account?

Cord is a combination of two HP 9000 K class servers running HP 10.20 Unix. The domain name cord.iupui.edu allows access to both servers. Cord maintains its file space on a shared Network File System (NFS) drive.

Cord's primary purpose is to provide a location for editing personal home pages served by Php for IUPUI faculty, staff, and students. Cord also provides access to newsgroups and IRC, and runs distance learning applications as well. To access Cord, you may use telnet, SSH, SCP, or FTP. The default account quota on Cord is 20MB.

All IUPUI students, staff, and faculty may have accounts on Cord. To create one, point your Web browser to the Network ID Services page:

Cyber Patrol is Internet filtering software that comes installed on many new PCs. The software has two high-performance filter engines that can filter out information on the Web that you don't want to see. You can customize it to fit criteria that you specify. You can find a complete list of criteria at:

Chinon America, Inc. reported in 1994 that a Trojan horse program linking itself to their company name had been found on the Internet. Trojan horse programs are destructive programs that trick the unsuspecting into executing them by pretending to be useful software.

This program, identified by the filename CD-IT.ZIP, claims to be a PC utility allowing you to use a Chinon CD-ROM drive as a CD burning device, which is technically impossible. In reality, this program, if executed, writes itself to your hard drive, where it destroys critical system files, then crashes your PC.

What is the Cholera virus?

The Cholera virus is a two-part executable worm, written in Visual C++, that can affect Windows 95, 98, and 2000 systems. Cholera's two components are the worm that carries the virus (W32.Cholera), and the virus itself (W32.CTX). Cholera spreads by copying itself to writable file shares and automatically sending itself as an e-mail attachment. Infected e-mail will have empty subject lines and will appear to be from legitimate past senders (i.e., people with whom the recipient has exchanged e-mail). Executing the worm's


			setup.exe

file from an e-mail attachment or from a file share will result in infection, barring the presence of updated antivirus software such as Norton AntiVirus.

According to Symantec, when Cholera's


			setup.exe

executes, the system becomes infected and the following message is displayed:

"Cannot open file: it does not appear to be a valid archive. If you downloaded this file, try downloading the file again."

UITS recommends that you always confirm the content of an e-mail message or attachment with the sender before you execute it. Even though Cholera does not appear to have spread rampantly, the execution of unconfirmed attachments is a primary means of spreading such viruses. Install virus protection software, and be sure to follow the instructions for updating virus file patterns and scanning for viruses.

Symantec

Trend Micro

Computer Associates Virus Encyclopedia

Also see:

The Common Object Request Broker Architecture (CORBA) is a set of specifications designed to support platform- and language-independent, object-oriented distributed computing. Similar in purpose to Microsoft's Distributed Component Object Model (DCOM), CORBA is a middleware technology, serving to connect diverse components of a software system. However, while DCOM is a proprietary technology, CORBA was devised by an assembly of over 800 corporations in the computing industry known collectively as the Object Management Group (OMG). The primary mission of the OMG is to support open standards, thereby encouraging interoperability between systems regardless of platform or implementation language. For example, CORBA makes it possible to integrate a legacy code base written in COBOL with a newly developed C++ application. A CORBA component written in Java and running under Linux can communicate seamlessly with another component written in C and running under Windows.

An Object Request Broker (ORB) is a software package that implements the CORBA standard. Some notable ORBs are:

Cobalt was a research-only computer for faculty and faculty-sponsored graduate students at Indiana University. On July 1, 2001, Cobalt was retired. Former Cobalt users can move to Steel or the Research SP for general research computing.

Cobalt was an HP Series 800 model K200 system with four CPUs, 1.9GB of real memory, and over 4GB of virtual memory, running HP-UX 10.20. This system was intended to provide an additional platform for researchers who already had access to Hewlett-Packard Unix systems in their labs or departments, but needed more horsepower. Cobalt allowed researchers to use their own HP-UX systems for development, then move seamlessly to Cobalt's central cycles for production.

A+ (A Plus) is an entry level computer certification for PC computer service technicians. The exam is designed to certify the competency of entry level PC computer service professionals in installing, maintaining, customizing, and operating personal computers.

The A+ certification is sponsored by CompTIA, which is the Computing Technology Industry Association (formerly ABCD: The Microcomputer Industry Association). CompTIA is a large trade group, founded in 1982 and made up of resellers, distributors, and manufacturers. It sets voluntary guidelines dealing with business ethics and professionalism, and is involved with many issues including product returns, warranty claims, and price protection.

The A+ exam contains situational, traditional, and identification types of questions. All of the questions are multiple choice, and there is only one answer for each question. The A+ exam is open to anybody, although it is designed to be taken by those with at least six months' job experience as service technicians.

The exam is divided into two sections or modules: a core module covering basic to advanced hardware knowledge of a wide range of computer concepts, and a DOS/Windows portion that tests competency in troubleshooting operating systems. Each module contains 60 to 70 questions, with a 90-minute time limit per module. A passing score is 75% for each module. You don't need to take both modules in the same sitting or back-to-back, but you must pass both modules within 90 calendar days of each other to receive the A+ designation. Once an individual is A+ certified, recertification is not required when the test is revised.

Currently, A+ is the only major non-vendor-specific hardware certification available for IBM-compatible computer systems. Increasingly, many help desk positions as well as service centers are requiring A+ certification or similar experience as a basis for hiring.

CompTIA also sponsors certification for document imaging (Certified Document Imaging Architech [CDIA]) and a network certification exam (Network+). The CompTIA certifications are in general more basic and less product-specific than other certifications, such as Microsoft's MCSE or a Novell CNE.

CompTIA formerly offered a Macintosh module and certificate in the repair and installation of Apple computer systems. This module has been discontinued for several years, and currently the only hardware certification for Macintosh computer systems is available through Apple. You can find more information on the Apple Service certification at:

You can take the A+ certification exam, as well as many other certifications, at a number of testing centers around the world. To register for an exam via one of these centers, Sylvan Prometric, please see Sylvan's online registration Web page at: