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was also harmless.
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The pack routines have been completely rewritten in ARCs
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numbered 2.00 or higher, and the checksum calculation is now
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more rigorous and will detect errors that would have gone
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un-noticed by ARCs 1.xx
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ARC 2.10
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In order to overcome the problem of XMODEM padding we
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made ARC 2.10 check for and ignore any padding at the end of
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an archive. Unfortunately, if the last entry in an archive
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happens to be only one block long, then ARC 2.10 is stupid
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enough to ignore it as XMODEM padding. This has been fixed
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in ARC 2.20.
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While we're on the subject of XMODEM padding...ARCs 1.xx
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can not handle it properly. The archive will still extract
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ok, but ARC may spit out some garbage at the end when it
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encounters the XMODEM padding and thinks it is another
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archive entry.
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Bless us ARC user for we have sinned. It has been six
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months since we first released ARC 1.00. For these and any
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other bugs we have failed to mention, we are truly sorry.
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ARC VERSION 2.20 PAGE - 8
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INTRODUCTION
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ARC was inspired by the program of the same name which
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has been available to MS-DOS users for some time now. It
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allows you to take several related files and back them up
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into a single archive file. The archive can later be
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extracted to obtain exact duplicates of the files that went
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into it. Since ARC automatically compresses the files as
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they are being archived, the resulting archive file takes up
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less disk storage space than the original files. Savings
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vary with the types of files being archived, and is
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typically 50% for text and 10-30% for program files.
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The primary advantage of ARC is as a backup tool. Word
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processing files, assembler source code, database files,
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graphics and music files compress rather well. In fact, due
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to their heavy use of graphics pictures, even games can
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squeeze down quit well in some instances. Normally a
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1541/4040 diskette has a capacity of 664 blocks of storage.
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Using ARC, you can increase this to the equivalent of about
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800 blocks for program disks and 1300 or more for text and
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graphics disks.
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Another big advantage of ARC is the fact that several
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files can be combined into a single archive. This makes it
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significantly easier (and faster) to transfer information
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from one computer to another via the telephone lines. If the
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bulletin board you are calling uses ARC files, you will
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spend less time reading directories and trying to figure out
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which, and how many files you have to download to get the
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program you want to work! Not only this, but after you
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extract the archive, all of the files will have the correct
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name and filetype so renaming files is not nessessary.
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ARC is also a useful tool for general file maintenance.
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Moving files between drives, renaming files, viewing
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directories, and the editing of simple text files is rather
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simple with ARC.
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ARC VERSION 2.20 PAGE - 9
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When Huffman coding is used to squeeze files, the
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compression ratio (the original length divided by the
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squeezed length) is about 1.11 for programs, 1.6 for text
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files, and can be 2.0 or more for graphics screens. Huffman
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coded files show up as 'squeezed' on an archive directory.
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Run-length squeezing ('packing') is sometimes more
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effective, particularly on graphical information.
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Version 2.00 of ARC introduced three new data
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compression methods. 'Squashing' combines run-length coding
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with Huffman squeezing and is generally superior to Huffman
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squeezing alone. 'Crunching' is by far the most interesting
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method used to date in that ARC will choose crunching as the
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most efficient compressor as often as 80 to 90% of the time.
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Crunched files are stored using the Lempel-Zev-Welch
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algorithm and can result in very impressive compression
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ratios. A typically text file will compress to about 45% of
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its original length, and word-pro or paperclip files will
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crunch down to about one third of their original length.
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Crunching combines run-length and Lempel-Zev-Welch
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compression and is unique in that it can be performed
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without requiring an initial pass through the data file. It
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