NetScape Navigator One-Day Course by Don Mayo, Kathy Berkemeyer, Cathy Vesecky |, Paperback | Barnes & Noble
NetScape Navigator One-Day Course

NetScape Navigator One-Day Course

by Don Mayo, Kathy Berkemeyer, Cathy Vesecky
     
 

Product Details

ISBN-13:
9781562435271
Publisher:
Ddc Pub
Publication date:
05/01/1997
Edition description:
SPIRAL
Pages:
600

Related Subjects

Read an Excerpt


EXERCISE 2

  • File Types
  • ASCII and Binary Files
  • Image Files
  • Multimedia files
  • Compressed Files
  • Encoded Files
  • Freeware
  • Shareware
  • and Public Domain Software
  • Avoid Viruses
  • Macro Viruses

NOTES

File Types

There are many types of files available at an FTP site. Among the most common are:

  • document files
  • executable files
  • image files
  • multimedia files

The above files are grouped by the kind of information they contain. But before we discuss these groups, let's distinguish between two broad file categories: ASCII files and binary files.

ASCII and Binary Files

If you classify files by the way they hold information, rather than by the kind of information they contain, there are two broad and important groups:
  • ASCII files contain only the typing characters and a few control
    • For this reason, ASCII files are also called "text" or "plain text" files. Almost every computer in the world can read, display, and print

    • Binary files-all other computer files-use all eight bits of the computer word. In fact, it's the eight-bit-word aspect that makes a binary file "binary" and not "ASCII." - When a program like e-mail tries to exchange a binary file, it treats it like an ASCII file, and ignores the last bit in each word. - Keep this distinction in mind when you read this section. It's often important to know which files are ASCII and which are binary. The usual length of a computer "word" is eight bits (i.e., eight 1s and 0s). But ASCII characters use only seven of those bits for their definition.

    Document files include simple ASCII text files and binary files associated with word processors and other programs. These files usually have the following extensions:

    • (no extension) Often an ASCII (or "plain text") file, including:
      • ReadMe files
      • FAQ (Frequently Asked Questions) files
      • mailing lists
    • .txt ASCII (or "plain text") file
    • .doc A generic "document" file, which can refer to:
      • ASCII text file * Microsoft Word binary
      • document file
    Executable files include all program files, usually with the following extensions:
    • .exe Executable DOS file or self-extracting zip file
    • .com Executable DOS file
    Self-extracting zip files have .exe extensions also. See the section called Compressed and Encoded Files later in this exercise for more information. Image files are binary files that contain pictures. These can be displayed by Web browsers and image programs like LViewPro and ACDSee95.

    Image files have these extensions:

    • .gif Graphics Interchange Format file; a common Internet
    • .jpg, jpeg Joint Photographic Experts Group file, a compressed

    • .tif Tagged Image Format (TIFF) file; a file type

    • .bmp Bitmap, file; Windows makes extensive use of bitmap

    • .pict Picture file; a file format associated with Macintosh

    • .eps Encapsulated PostScript file; a file format for Adobe

      Multimedia Files

      video, sound, and music. These include:
      • .mpg, .mpeg MPG file, a video format; requires special software

      • .save Windows video format; can be immediately viewed in

      • .mov QuickTime video format; a Macintosh format often

      • .wav Sound format. Wave files often contain speech and

      • .mid, .midi MIDI format music files; requires a MIDI driver for

        Compressed Files

        Small files can be transferred easily and quickly using FTP, Large files, many megabytes in size, take a long time to transfer. To make large files smaller and easier to download, FTP sites often contain compressed files--files that have been made smaller with a file compression program.

        On PCs, files are frequently compressed with a program called PKZIP. Files compressed with PKZIP are called zip files. To unzip these files, you need the companion program PKUNZIP. (A Mac version of PKZIP, called Ziplt, is also available.)

        Some zip files are self-extracting. You don't need any program to extract their contents, since they extract themselves when executed. Selfextracting zip files are created with the program ZIP2EXE.

        You can find and download PKZIP by doing a Web search on the program name.

        On Macs, compressed files are frequently created by a program called StuffIt. These files are called stuffed files or sit files (because they have the extension sit).

        You need Stuff It to unstuff them.

        Some Mac compressed files are self-extracting archives. Like selfextracting zip files, these files extract themselves when executed. Selfextracting archives are produced by a number of programs, including CompactPro.

        Compressed files have these extensions:

        • .zip Files compressed with PKZIP. These files must be

        • .exe Self-extracting zip file. These files uncompress

        • .sit Files compressed with Stuff It. These files must be

        • .sea Self-extracting archive file. These files uncompress

          Encoded Files

          • Some binary files are encoded-changed from binary format to ASCII format. Encoding is necessary for files that must pass through e-mail and files that are posted to newsgroups.

          • Even though encoded files are meant to be e-mailed, you can download or upload an encoded file using FTP.

          • Two common encoding schemes for binary files are UUencoding and MIME (or Base64) encoding.

          • Encoded files always are ASCII when viewed, though the two encoding schemes each produce files with a different "look."

          • File extensions vary for encoded files, since decoders usually recognize encoded files by their contents, not by their extension.

          • If you download an encoded file, you must decode it (change it back to binary format) before it can be used.

          • Programs for decoding files can be found on many FTP sites. Most Web browsers and e-mail programs can decode files for you.

          Freeware, Shareware, and Public Domain Software

          • Freeware is software that you can download and use for free. Freeware programs have an owner, but you do not have to buy a license or purchase a disk before you can use them. Freeware can be copied and distributed legally.

          • One type of freeware is called public domain software. Public domain software can be copied and distributed for free. Public domain software has no owner-the "public" owns it.

          • Shareware is also software that you can download for free. But unlike freeware, shareware is made available by its owners only for a limited time so that you can evaluate its usefulness. After the evaluation period, you are expected to purchase the shareware, which is usually inexpensive, or stop using it.

          • Sometimes shareware works on the honor system, and sometimes it stops working after the evaluation period is over.

          • Shareware often comes with online documentation that tells you how you can register your copy of the software. Usually, registering the shareware entitles you to get support and updates as they come out.

          Avoid Viruses

          • Among the hazards of sharing files-either by exchanging disks or passing them back and forth across the Internet-are small computer programs called viruses.

          • Viruses are computer programs that attach themselves secretly to other programs and are activated when the host program is executed.

          • Viruses usually perform some unwanted action, ranging from nuisance to destruction. Some viruses, for example, simply display a message at predetermined times. Other viruses attempt to reformat your hard disk and destroy all your data. . . .

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