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Lesson Plan |
| IMOS Home | Student Center | TallTech Home |
|
Title |
Information Resources on the Web |
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Time Allotment |
3 hrs |
Read chapter 5 from Internet Comprehensive
Additional references/information (from book source) can be found at
http://www.course.com/downloads/NewPerspectives/internet/cmp/t05.html
Common Internet File Formats (HTM) - fairly complete list of formats out there
Please note: Some documents are a little dated, but conceptually the same.
Information Resources
WINZIP
Opening an existing archive.
Viewing files in the archive.
Extracting files in the archive.
Creating new archives.
Adding files to an existing archive.
Deleting files from an existing archive.
Configuring WinZIP
Passwords
With text files, most text editors can be used to access the file.
With binary files, programs specifically used to read the binary must be used.
Binary files can take the
form of compressed files, executable files, sound files, graphic files, word
processing documents, spreadsheets, etc.
Large files, which may be graphics, audio, video or text
information, often take several minutes to transfer or download over the
Internet. To make more efficient use of space and to speed things up, most large
files are compressed. This can often cut download or transfer time by as much as
half.
How does compression work? Compression software uses
complex mathematical equations to scan a file for repeating patterns in the
data. It replaces the repeating data with smaller codes that take up fewer
bytes. For example, one way compression software works is to replace repeating
text characters with a code and notes the code's positions in the document.
Compression is used to reduce the amount of space required
to store information, and to reduce the amount of time required to download
data. There are two types of compression: "lossy" and "lossless."
Lossy compression is usually very high data reduction, but loses some of the
data quality upon de-compression by the receiving computer. Lossless compression
uses very careful mathematical rules (called "algorithms") to
reorganize the data so that it can be accurately de-compressed.
There are a number of common compression types used for different data types:
JPEG
The Joint Photographic Experts Group standard is used to compress still images. Known limitations of the human eye, that color details are less important than contrast (light-dark) and let those details be compressed to a greater degree. JPEG is best for photos with subtle shading.
GIF
General Image Format, created by CompuServe to store images, reduces color bit depth to 8 bits (256 colors). GIF is best for line art or simple "cartoon" images.
Archives
These programs take several input files (even entire data directories), compress them and produces a single archive file. Examples are ARC, ARJ, LHA, ZIP, ZOO.
LZW
Based on the work of pioneers Lempel, Ziv, and Welch at Unisys. (see http://www.cis.ohio-state.edu/hypertext/faq/usenet/compression-faq/ for details on the patents). A variation of LZW is used in the V.42bis modem standard for data transmission.
MPEG
Moving Picture Experts Group standards for video, not only compresses each frame, but also predicts frame-to-frame images by ignoring redundant non-changing pixels, and storing only variations between frames
| ZIP Files | PKZIP / WinZip |
| Compressed Files (.Z) | Unix Compressed File |
| TAR Files | Unix program takes separate files and makes one file. |
| LZH Files | LHA Archive |
There are three main types of compression used on Unix systems: zip, compress, tar.
Take
the example (filename.tar.Z) you
would need to undo the compression from left to right. The '.Z' indicates
compress via 'compress', you'd enter 'uncompress filename.tar.Z' to undo it. You
should be left with 'filename.tar'. The '.tar' indicates the use of 'tar' (Unixesse
for Tape ARchive). To undo this enter 'tar -xf filename.tar'. 'tar' is typically
used to bundle a series of files so undoing '.tar' will likely result in the
creation of a bunch of files.
The zip compression is indicated by a '.zip' extension, undone with 'unzip'. A
closely related, in fact compatible, command is 'pkzip'. This is a public domain
version found frequently on IBM and compatible platforms.