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ARC
File Archive Utility
Version 5.1
(C) COPYRIGHT 1985, 1986 by System Enhancement Associates;
ALL RIGHTS RESERVED
This document describes the ARC file utility, version 5.1, which was
created by System Enhancement Associates in January of 1986.
Table of Contents Table of Contents
Introduction .................................................... 1
Using ARC ....................................................... 3
ARC commands .................................................... 4
Adding files ................................................ 4
Extracting files ............................................ 6
Deleting files .............................................. 6
Listing archive entries ..................................... 7
Printing files .............................................. 9
Running files ............................................... 9
Testing an archive .......................................... 10
Converting an archive ....................................... 10
ARC options ..................................................... 11
Suppressing compression ..................................... 11
Backup retention ............................................ 12
Message suppression ......................................... 13
Encryption/decryption ....................................... 14
RAMdisk support ................................................. 15
MARC ............................................................ 16
XARC ............................................................ 17
Version numbers ................................................. 18
Program update service .......................................... 19
Common questions and answers .................................... 20
Revision history ................................................ 22
Changes in version 3 ........................................ 22
Changes in version 4 ........................................ 22
Changes in version 4.1 ...................................... 23
Changes in version 4.3 ...................................... 23
Changes in version 4.4 ...................................... 24
Changes in version 4.5 ...................................... 24
Changes in version 5.0 ...................................... 25
Changes in version 5.1 ...................................... 26
Program history and credits ..................................... 27
Site license .................................................... 28
Order form ...................................................... 30
INTRODUCTION INTRODUCTION
ARC is the copyrighted property of System Enhancement Associates. You
are granted a limited license to use ARC, and to copy it and
distribute it, provided that the following conditions are met:
1) No fee may be charged for such copying and distribution.
2) ARC may ONLY be distributed in its original, unmodified state.
Any voluntary contributions for the use of this program will be
appreciated, and should be sent to:
System Enhancement Associates
21 New Street
Wayne, NJ 07470
You may not use this product in a commercial environment or a
governmental organization without paying a license fee of $35. Site
licenses and commercial distribution licenses are available. A
program disk and printed documentation are available for $50. See the
order form in the back of this manual for more details.
A word about user supported software:
freeware The user supported software concept (usually referred to as freeware)
is an attempt to provide software at low cost. The cost of offering a
new product by conventional means is staggering, and hence dissuades
many independent authors and small companies from developing and
promoting their ideas. User supported software is an attempt to
develop a new marketing channel, where products can be introduced at
low cost.
If user supported software works, then everyone will benefit. The
user will benefit by receiving quality products at low cost, and by
being able to "test drive" software thoroughly before purchasing it.
The author benefits by being able to enter the commercial software
arena without first needing large sources of venture capital.
But it can only work with your support. We're not just talking about
ARC here, but about all user supported software. If you find that you
are still using a program after a couple of weeks, then pretty
obviously it is worth something to you, and you should send in a
contribution.
ARC Page 1
And now, back to ARC:
ARC is used to create and maintain file archives. An archive is a
group of files collected together into one file in such a way that the
individual files may be recovered intact.
ARC is different from other archive and library utilities in that it
automatically compresses the files being archived, so that the
resulting archive takes up a minimum amount of space.
When ARC is used to add a file to an archive it analyzes the file to
determine which of four storage methods will result in the greatest
savings. These four methods are:
1) No compression; the file is stored as is.
2) Repeated-character compression; repeated sequences of the same byte
value are collapsed into a three-byte code sequence.
3) Huffman squeezing; the file is compressed into variable length bit
strings, similar to the method used by the SQ programs.
4) Dynamic Lempel-Zev compression; the file is stored as a series of
variable size bit codes which represent character strings, and
which are created "on the fly".
Note that since one of the four methods involves no compression at
all, the resulting archive entry will never be larger than the
original file.
An interesting note: It has been brought to our attention that BASIC
not programs compress to a smaller size when they are not tokenized. If
you are more concerned with space than speed, you may wish to convert
your BASIC programs to ASCII form before adding them to an archive.
Your BASIC manual should give instructions on how to do this.
ARC Page 2
USING ARC USING ARC
ARC is invoked with a command of the following format:
ARC <x> <arcname> [<template> . . .]
Where:
<x> is an ARC command letter (see below), in either upper or lower
case.
<arcname> is the name of the archive to act on, with or without an
extension. If no extension is supplied, then ".ARC" is assumed.
The archive name may include path and drive specifiers.
<template> is one or more file name templates. The "wildcard"
characters "*" and "?" may be used. A file name template may
include a path or drive specifier, though it isn't always
meaningful.
If ARC is invoked with no arguments (by typing "ARC", and pressing
"enter"), then a brief command summary is displayed.
Following is a brief summary of the available ARC commands:
a = add files to archive
m = move files to archive
u = update files in archive
f = freshen files in archive
d = delete files from archive
x,e = extract files from archive
r = run files from archive
p = copy files from archive to standard output
l = list files in archive
v = verbose listing of files in archive
t = test archive integrity
c = convert entry to new packing method
Following is a brief summary of the available ARC options, which may
alter how a command works:
b = retain backup copy of archive
s = suppress compression (store only)
w = suppress warning messages
n = suppress notes and comments
g = encode or decode archive entry
ARC Page 3
ARC COMMANDS ARC COMMANDS
This section describes each of the commands. ARC will accept any one
command at a time. If no commands are given, then a brief command
list is displayed.
____________ ADDING FILES
Files are added to an archive using the "A" (Add), "M" (Move), "U"
(Update), or "F" (Freshen) commands. Add always adds the file. Move
differs from Add in that the source file is deleted once it has been
added to the archive.
Update differs from Add in that the file is only added if it is not
already in the archive, or if it is newer that the corresponding entry
in the archive.
Freshen is similar to Update, except that new files are not added to
the archive; only files already in the archive are updated.
For example, if you wish to add a file named "TEST.DAT" to an archive
named "MY.ARC", you would use a command of the form:
ARC a my test.dat
If you wanted to add all files with a ".C" extension, and all files
named "STUFF" to an archive named "JUNK.ARC", you could type:
ARC a junk *.c stuff.*
If you wanted to move all files in your current directory into an
archive named "SUM.ARC", you could use a command of the form:
ARC m sum *.*
If you have an archive named "TEXT.ARC", and you wanted to add to it
all of your files with an extension of ".TXT" which have been created
or changed since they were last archived, then you would type:
ARC u text *.txt
If you have a bunch of files in your current directory, with backup
copies being stored in an archive named "SAFE.ARC", then if you wanted
to make sure that every file in the archive is the latest version of
that file, you would type:
ARC f safe
ARC Page 4
A word about Update and Freshen: These are similar in that they look
at the date and time of last change on the file, and only add it if
the file has been changed since it was last archived. They differ in
that Update will add new files, while Freshen will not.
In other words, Update looks for the files on disk, and adds them if
they are new or have changed, while Freshen looks in the archive, and
tries to update the files which are already there.
Archive entries are always maintained in alphabetic order. Archive
entries may not have duplicate names. If you add a file to an archive
that already contains a file by that name, then the existing entry in
the archive is replaced. Also, the archive itself and its backup will
not be added.
You may also add a file which is in a directory other than your
current directory. For example, it is perfectly legal to type:
ARC a junk c:\dustbin\stuff.txt
You cannot add two files with the same name. In other words, if you
have a file named "C:\DUSTBIN\STUFF.TXT" and another file named
"C:\BUCKET\STUFF.TXT", then typing:
arc a junk c:\dustbin\*.* c:\bucket\*.*
will not work.
ARC does not save the path name. In other words, if you specify a
drive and/or path when adding a file, only the actual file name is
stored in the archive.
ARC will never add an archive to itself, nor will it add the temporary
copy or a backup copy of the archive.
ARC Page 5
________________ EXTRACTING FILES
Archive entries are extracted with the "E" (Extract) and "X" (eXtract)
commands. For example, if you had an archive named "JUNK.ARC", and
you wanted all files in it with an extension of ".TXT" or ".DOC" to be
recreated on your disk, you could type:
ARC x junk *.txt *.doc
If you wanted to extract all of the files in an archive named
"JUNK.ARC", you could simply type:
ARC x junk
Whatever method of file compression was used in storing the files is
reversed, and uncompressed copies are created in the current
directory.
You can also specify a path name, in which case the decompressed copy
is placed in the specified directory. For example, if you had an
archive named "JUNK.ARC", and you wanted all files in it with an
extension of ".TXT" to be placed in the directory "C:\WASTE\LAND",
then you could type:
ARC x junk c:\waste\land\*.txt
If you wanted to put the file "TRASH.TXT" on your A: drive, and the
file "LITTER.TXT" on your B: drive, you could type:
ARC x junk a:trash.txt b:litter.txt
If you give more than one path for a file, then only the first one is
used. For example, if you typed:
ARC x junk a:trash.txt b:trash.txt
then TRASH.TXT will be placed on your A: drive.
______________ DELETING FILES
Archive entries are deleted with the "D" (Delete) command. For
example, if you had an archive named "JUNK.ARC", and you wished to
delete all entries in it with a filename extension of ".C", you could
type:
ARC d junk *.c
ARC Page 6
_______________________ LISTING ARCHIVE ENTRIES
You can obtain a list of the contents of an archive by using the "L"
(List) command or the "V" (Verbose list) command. For example, to see
what is in an archive named "JUNK.ARC", you could type:
ARC l junk
If you are only interested in files with an extension of ".DOC", then
you could type:
ARC l junk *.doc
ARC prints a short listing of an archive's contents like this:
Name Length Date
============ ======== =========
ALPHA.TXT 6784 16 May 85
BRAVO.TXT 2432 16 May 85
COCO.TXT 256 16 May 85
==== ========
Total 3 9472
"Name" is simply the name of the file.
"Length" is the unpacked file length. In other words, it is the
number of bytes of disk space which the file would take up if it were
extracted.
"Date" is the date on which the file had last been modified, as of the
time when it was added to the archive.
"Total" is pretty obvious, I think.
ARC prints a verbose listing of an archive's contents like this:
Name Length Stowage SF Size now Date Time CRC
============ ======== ======== ==== ======== ========= ====== ====
ALPHA.TXT 6784 Squeezed 35% 4413 16 May 85 11:53a 8708
BRAVO.TXT 2432 Squeezed 41% 1438 16 May 85 11:53a 5BD6
COCO.TXT 256 Packed 5% 244 16 May 85 11:53a 3AFB
==== ======== ==== ========
Total 3 9472 27% 6095
"Name", "Length", and "Date" are the same as for a short listing.
"Stowage" is the compression method used. The following compression
methods are currently employed:
-- No compression.
Packed Runs of repeated byte values are collapsed.
Squeezed Huffman squeeze technique employed.
Crunched Lempel-Zev compression technique employed.
ARC Page 7
"SF" is the stowage factor. In other words, it is the percentage of
the file length which was saved by compression. The total stowage
factor is the stowage factor for the archive as a whole, not counting
archive overhead.
"Size now" is the number of bytes the file is occupying while in the
archive.
"Time" is the time of last modification, and is associated with the
date of last modification.
"CRC" is the CRC check value which has been stored with the file.
Another CRC value will be calculated when the file is extracted or
tested to ensure data integrity. There is no especially good reason
for displaying this value.
ARC Page 8
______________ PRINTING FILES
Archive entries may be examined with the "P" (Print) command. This
works the same as the Extract command, except that the files are not
created on disk. Instead, the contents of the files are written to
standard output. For example, if you wanted to see the contents of
every ".TXT" file in an archive named "JUNK.ARC", but didn't want them
saved on disk, you could type:
ARC p junk *.txt
If you wanted them to be printed on your printer instead of on your
screen, you could type:
ARC p junk *.txt >prn
_____________ RUNNING FILES
Archive entries may be run without being extracted by use of the "R"
(Run) command. For example, if you had an archive named "JUNK.ARC"
which contained a file named "LEMON.COM", which you wished to run, you
could type:
ARC r junk lemon
You can run any file from an archive which has an extension of ".COM",
".EXE", ".BAT", or ".BAS". You do not have to specify the extension,
but all matching files are run if you do not. In other words, if you
had an archive named "JUNK.ARC" which contained the files "LEMON.COM",
"LEMON.EXE", and "LEMON.BAS", and you typed:
ARC r junk lemon
Then all three programs will be run. You can avoid this by specifying
an extension in this case.
You cannot give arguments to a program you are running from an
archive. Also, you will need a fair amount of memory to run a program
from an archive. It probably cannot be done with less than 256k.
In practice, the file to be run is extracted, run, and then deleted.
ARC Page 9
__________________ TESTING AN ARCHIVE
The integrity of an archive may be tested by use of the "T" (Test)
command. This checks to make sure that all of the file headers are
properly placed, and that all of the files are in good shape.
This can be very useful for critical archives, where data integrity
must be assured. When an archive is tested, all of the entries in the
archive are unpacked (without saving them anywhere) so that a CRC
check value may be calculated and compared with the recorded CRC
value.
For example, if you just received an archive named "JUNK.ARC" over a
phone line, and you want to make sure that you received it properly,
you could type:
ARC t junk
It defeats the purpose of the T command to combine it with N or W.
_____________________ CONVERTING AN ARCHIVE
The "C" (Convert) command is used to convert an archive entry to take
advantage of newer compression techniques. This is occasionally
desirable when a new version of ARC is released. Please refer to the
revision history section for details on when new compression methods
were implemented.
For example, if you had an archive named "JUNK.ARC", and you wanted to
make sure that all files with an extension of ".DOC" were encoded
using the very latest methods, you could type:
ARC c junk *.doc
Or if you wanted to convert every file in the archive, you could type:
ARC c junk
ARC Page 10
ARC OPTIONS ARC OPTIONS
This section describes the options which are available to modify how
ARC works. Any of these options can be combined with any of the
commands, though the result may not always be something you'd want to
do.
_______________________ SUPPRESSING COMPRESSION
The "S" (Suppress compression) option can be combined with any command
that updates archive entries. These include Add, Move, Update,
Freshen, and Convert. The effect of the S option is to prevent any
compression techniques from being employed. This is intended to allow
you to add a few files at a time to an archive quickly, and then later
convert the archive to compress everything at once.
For example, over the course of a day you might give each of the
following commands:
ARC as junk *.txt
ARC as junk *.mac
ARC as junk *.doc
At the end of the day, when you have finished adding things to the
archive, you could have all of the archive entries compressed at once
by typing:
ARC c junk
You could also decompress the archive by typing:
ARC cs junk
though I can't imagine why you'd want to.
ARC Page 11
________________ BACKUP RETENTION
When ARC changes an archive (during an Add, Move, Update, Freshen,
Delete, or Convert) it creates a new archive with the same name, but
with an extension of ".$$$". For example, if you add a file to an
archive named STUFF.ARC, then ARC will create a new archive named
STUFF.$$$. ARC will read from your existing archive and write out the
new archive with any changes to the ".$$$" copy.
Normally when ARC is finished it deletes the original and renames the
new archive to the original name (ie. STUFF.ARC goes away, and
STUFF.$$$ becomes the new STUFF.ARC). Among other things, this means
that if anything goes wrong and ARC is unable to finish, then your
original archive will still be intact.
In some circumstances you may wish to retain the original version of
the archive as a backup copy. You can do this easily by using the
Backup option. Add the letter "B" to your command, and ARC will
rename your original archive to have an extension of ".BAK" instead of
deleting it.
In other words, if you wanted to add "WASTE.TXT" to an archive named
"JUNK.ARC", but wanted to keep a backup copy, then you would type:
ARC ab junk waste.txt
Your original archive would become "JUNK.BAK", while "JUNK.ARC" would
contain the new "WASTE.TXT" file.
If you keep a backup of an archive which already has a backup, then
the older backup copy is deleted.
ARC Page 12
___________________ MESSAGE SUPPRESSION
ARC prints three types of messages: warnings, comments, and errors.
Warnings are messages about suspected error conditions, such as when a
file to be extracted already exists, or when an extracted file fails
the CRC error check. Warnings may be suppressed by use of the "W"
(Warn) command. You should use this command sparingly. In fact, you
should probably not use this command at all.
Comments (or notes) are informative messages, such as naming each file
as it is added to the archive. Comments and notes may be suppressed
by use of the "N" (Note) command.
Errors are actual system problems, such as running out of disk space.
You cannot suppress errors.
For example, suppose you extracted all files with an extension of
".BAS" from an archive named "JUNK.ARC" Then, after making some
changes which you decide not to keep, you decide that you want to
extract them all again, but you don't want to be asked to confirm
every one. In this case, you could type:
ARC xw junk *.bas
Or, if you are going to add a hundred files with an extension of
".MSG" to an archive named "TRASH.ARC", and you don't want ARC to list
them as it adds them, you could type:
ARC an trash *.msg
Or, if you want to extract the entire contents of an archive named
"JUNK.ARC", and you don't want to hear anything, then type:
ARC xnw junk
ARC Page 13
_____________________ ENCRYPTION/DECRYPTION
Archive entries may be encrypted and decrypted by using the "G"
(Garble) option. The Garble option takes the remainder of the command
last string as the password to use, so it must be the last option.
For example, if you wanted to add a file named "WASTE.TXT" to an
archive named "JUNK.ARC", and you wanted to encrypt it using the
password "DEBRIS", then you would type:
ARC agdebris junk waste.txt
Later on, when you want to extract it again, you would type:
ARC xgdebris junk waste.txt
The password you supply is used to encrypt (or decrypt) the archive
entry by performing an exclusive OR between each byte of the packed
data and each byte of the password. The password can be any length,
and each of its bytes is used in rotation. The password is converted
not to uppercase before it is used, so it is not case sensitive. Since
the encryption is performed on the packed data, it has no effect on
stowage factors.
This is not a particularly sophisticated means of encryption, and it
is theoretically possible to crack. Still, since it is performed on
the packed data, the result should be quite sufficient for casual use.
You can, if you wish, use different passwords for different files in
an archive, but we advise against it. If you are going to encrypt an
archive, we suggest you use the same password for every file, and give
the password whenever you do anything at all with the archive. It is
possible to list the entries in an encrypted archive using the "L" and
"V" commands without giving the password, but nothing else will work
properly.
We advise that you use this option sparingly, if at all. If you
should forget or mistype your password, it is highly unlikely that you
will ever recover your data.
ARC Page 14
RAMDISK SUPPORT RAMDISK SUPPORT
If you have a RAMdisk, or other high-speed storage, then you can speed
up ARC somewhat by telling it to put its temporary files on the
RAMdisk. You do this by setting the ARCTEMP environment string with
the MS-DOS SET command. For example, if drive B: is your RAMdisk,
then you would type:
set ARCTEMP=B:
Refer to the MS-DOS manual for more details about the SET command.
You need only set the ARCTEMP string once, and ARC will use it from
then on until you change its value or reboot your system.
If ARC does not find an environment string named ARCTEMP, then it
looks for one named TEMP to use instead. Several packages already use
the TEMP string for exactly this purpose. If you have need of an
environment string named TEMP for something else, then you should be
sure to define ARCTEMP.
There are a limited number of temporary files created by ARC. The one
most often used is "$ARCTEMP.CRN", which is created (if possible) when
adding a file to an archive. The Convert command uses a file named
"$ARCTEMP.CVT" to hold each file as it is being converted. The Run
command also creates a temporary file, which has the name "$ARCTEMP",
and whose extension matches that of the file being run.
ARC Page 15
MARC MARC
MARC is a separate program which is used to merge archives created by
ARC. MARC moves files from one archive to another without unpacking
them.
MARC is used as follows:
MARC <target> <source> [<template> . . .]
Where:
<target> is the name of the archive to add files to.
<source> is the name of the archive to read files from.
<template> is one or more file name templates. The wildcard
characters "*" and "?" may be used. If no template is supplied,
then all of the files in <source> are added to <target>.
It is not necessary for the target to exist. If it does not exist,
then it is created. Thus, MARC can be used as an "extractor" as well
as a "merger".
For example, if you wanted to create an archive named "JUNK.ARC",
which is to contain all of the files with an extension of ".TXT" which
are currently contained in another archive named "WASTE.ARC", then you
could type:
MARC junk waste *.txt
If you wanted to create an archive named "JUNK.ARC", which is to
contain all of the files currently in the archives "WASTE.ARC" and
"TRASH.ARC", you could type:
MARC junk waste
MARC junk trash
Though it would probably be faster to type:
COPY waste.arc junk.arc
MARC junk trash
If MARC is invoked with no arguments, then it gives brief directions
in its use.
ARC Page 16
XARC XARC
XARC is a separate program which is used to extract all files from one
or more archives. It doesn't do anything that ARC doesn't do, and it
isn't any faster, but it may be preferred in certain cases, as it is
much smaller than ARC.
XARC is used as follows:
XARC <arcname> . . .
Where <arcname> is the name of one or more archives. The wildcard
characters "*" and "?" may be used. All files are extracted from the
named archives.
For example, if you wanted to extract everything from two archives
named "WASTE.ARC" and "JUNK.ARC", you could type:
XARC waste junk
If you wanted to extract every file from every archive in a
subdirectory named "TRASH", you could type:
XARC trash\*.arc
If XARC is invoked with no arguments, then it gives brief directions
in its use.
ARC Page 17
VERSION NUMBERS VERSION NUMBERS
There seems to be some confusion about our version numbering scheme.
All of our version numbers are given as a number with two decimal
places.
The units indicate a major revision, such as adding a new packing
algorithm.
The first decimal place (tenths) indicates a minor revision that is
not essential, but which may be desired.
The second decimal place (hundredths) indicates a trivial revision
that will probably only be desired by specific individuals or by die-
hard "latest version" fanatics.
ARC also displays its date and time of last edit. A change of the
date and time without a corresponding change in version number
indicates a truly trivial change, such as fixing a spelling error.
To sum up: If the units change, then you should get the newer version
as soon as you can. If the tenths change, then you may want to get
the newer version, but there's no hurry. If anything else changes,
then you probably shouldn't bother. This is reflected by our own
habit of referring to "version 4.5" instead of "version 4.52".
ARC Page 18
PROGRAM UPDATE SERVICE PROGRAM UPDATE SERVICE
A license to ARC entitles you to use all future versions of ARC. New
versions are generally available through normal freeware distribution
channels, and we prefer that you obtain them that way. However, many
users of ARC have written to ask us about an update service.
A program disk containing the latest version is returned on every
order of $50 or more. If you wish to purchase a single-user license
and want an update disk, please enclose a check or money order for $50
instead of $35.
For a fee of $50 per year you can subscribe to our program update
service. Subscribers get up to five program updates per year mailed
to them as new versions come out. This does not include trivial
releases.
ARC Page 19
COMMON QUESTIONS AND ANSWERS COMMON QUESTIONS AND ANSWERS
Here are some of the more common questions we've received about ARC,
along with their answers:
Q: Why do you bother with squeezing when crunching is so much faster?
A: Because crunching isn't really as fast as it looks. Crunching is a
one pass operation, while squeezing requires two passes. ARC
actually does the crunching during the analysis pass, and puts the
crunched output in a file named "$ARCTEMP.CRN". If crunching turns
out to be the best method, then this temporary file is copied into
the new archive. In other words, when ARC says "crunching" it
isn't really crunching, it's just copying a file.
much Also, there are a lot of files out there that squeeze much better
than they crunch.
Q: Why does ARC run out of room if I make an archive bigger than about
180k?
A: Because you are working on a floppy disk. ARC creates a copy of
your archive, incorporating any new files as it goes. When it is
done, it deletes the original and renames the new one. There are a
number of reasons for doing it this way, one being that your
original archive is still intact if anything happens while ARC is
running. ARC also needs room for the temporary file used in
crunching.
You can save some space by using the ARCTEMP environment string to
put the temporary file on another disk, as well as using drive
specifiers and having the archive and the files to add on separate
disks, but you still won't be able to make an archive larger than
about 180k. If you need to make a larger archive, and if you have
a fixed disk, then you can create the archive on the fixed disk and
then copy it to the floppy.
Q: I've seen an ARC.COM and an ARC.EXE. Which one is the right one?
A: ARC.EXE. One or more people have been running ARC through a
utility that converts an ".EXE" file to a ".COM" file. But this
space utility is designed to save space, not speed. On ARC it saves
about 250 bytes, and makes no measurable difference in program
speed. We've decided that the savings are not worth the extra step
in development in this case.
ARC Page 20
Q: Can I use ARC to distribute my public domain or freeware program?
A: Yes, of course.
Q: Can I use ARC to distribute my commercial software package?
A: Yes. Please contact us for a commercial distribution license.
Q: I'm a commercial user. Why should I pay for freeware that others
get for free?
all A: Because you cannot credibly plead poverty. Freeware, all freeware,
is an attempt to develop a new marketing channel to the benefit of
everyone. You can still "test drive" freeware for a short period,
but if you decide to use it in your business, then you should pay
for it.
Q: Why not allow me to select which method of compression I want ARC
to use?
A: It would needlessly complicate ARC, both internally and in use.
The exact nature of the compression methods used are complex, and
quite different. The only sure way to tell which will be best in
any given case is to analyze the data, as ARC does. The method
chosen may not always be what you expect.
Q: How can I get the latest version of ARC?
A: ARC updates are distributed through normal freeware channels, and
by FidoNet. We also ship a program update disk on every order of
$50 or more. In addition, we also offer an update subscription
service. See the previous section for more details.
ARC Page 21
REVISION HISTORY REVISION HISTORY
____________________ CHANGES IN VERSION 3
The function used to calculate the CRC check value in previous
versions has been found to be in error. It has been replaced with the
proper function. ARC will still read archives created with earlier
versions of ARC, but it will report a warning that the CRC value is in
error. All archives created prior to version 3.0 should be unpacked
and repacked with the latest version of ARC.
Transmitting a file with XMODEM protocol rounds the size up to the
next multiple of 128 bytes, adding garbage to the end of the file.
This used to confuse ARC, causing it to think that the end of the
archive was invalidly formatted. This has been corrected in
version 3.01. Older archives may still be read, but ARC may report
them to be improperly formatted. All files can be extracted, and no
data is lost. In addition, ARC will automatically correct the problem
when it is encountered.
____________________ CHANGES IN VERSION 4
ARC is adding another data compression technique in this version. We
have been looking for some technique that could improve on Huffman
squeezing in at least a few cases. So far, Lempel-Zev compression
seems to be fulfilling our fondest hopes, often achieving compression
rates as much as 20% better than squeezing, and sometimes even better.
Huffman squeezing depends on some bytes being more "popular" than
others, taking the file as a whole. Lempel-Zev compression is instead
looking for strings of bytes which are repeated at various points
(such as an end of line followed by spaces for indentation). Lempel-
Zev compression is therefore looking for repetition at a more "macro"
level, often achieving impressive packing rates.
In the typical case a file is added to an archive once and then
extracted many times, so the increased time for an update should more
than pay for itself in increased disk space and reduced file
transmission time.
As usual, ARC version 4.0 is completely upward compatible. That is,
it can deal properly with any archive created by any earlier version
of ARC. It is NOT reverse compatible. Archives created by ARC 4.0
will generally not be usable by earlier versions of ARC.
ARC Page 22
______________________ CHANGES IN VERSION 4.1
Lempel-Zev coding has been improved somewhat by performing non-repeat
compression on the data before it is coded (as was already done with
Huffman squeezing). This has the two fold advantage of (a) reducing
to some extent the amount of data to be encoded, and (b) increasing
the time it takes for the string table to fill up. Performance gains
are small, but noticeable.
The primary changes are in internal organization. ARC is now much
"cleaner" inside. In addition to the aesthetic benefits to the
author, this should make life easier for the hackers out there. There
is also a slight, but not noticeable, improvement in overall speed
when doing an update.
Version 4.1 is still fully upward compatible. But regretfully, it is
again not downward compatible. Version 4.1 can handle any existing
archive, but creates archives which older versions (including 4.0)
cannot unpack.
______________________ CHANGES IN VERSION 4.3
Version 4.3 adds the much-demanded feature of using pathnames when
adding files to an archive. For obscure technical reasons, files
being extracted still go in the current directory on the current
drive. Pathnames are also not supported for any of the other
commands, because it would make no sense.
Version 4.3 is also using a slightly different approach when adding a
file to an archive. The end result is twofold:
1) Slightly more disk space is required on the drive containing the
archive. This should only be noticeable to those creating very
large archives on a floppy based system.
2) A 30% reduction in packing time has been achieved in most cases.
This should be noticeable to everyone.
As always, version 4.3 is still fully upwards compatible, and is
backwards compatible as far as version 4.1.
ARC Page 23
______________________ CHANGES IN VERSION 4.4
The temporary file introduced in version 4.3 occasionally caused
problems for people who had not added a FILES= statement to their
CONFIG.SYS file. This has now been corrected. Also, support of the
ARCTEMP environment string was added to allow placing of the temporary
file on a RAMdisk.
A bug was reported in the Run command, which has been fixed. From the
nature of the bug, and the extreme time required before the bug was
reported, it is deduced that the Run command is probably the least
used feature of ARC.
The Update command was changed. It is no longer a straight synonym
for Add. Instead, Update now only adds a file if it is newer than the
version already in the archive, as shown by the MS-DOS date/time
stamp.
______________________ CHANGES IN VERSION 4.5
The Convert command was not making use of RAMdisk support. Now it is.
The Freshen command was added. Our first choice for a name was
Refresh, but we already had a Run command. Assuming that you have an
archive which already contains everything you want in it (for software
distribution, perhaps), then Freshen would be used to update the
archive. It was pointed out to us that ARC already knows what is in
the archive, so it should be able to look on disk for newer versions.
Now it can.
The Suppress compression option was added by popular demand. It
allows files to be added quickly to an archive, since the files are
not analyzed or compressed, but merely stored straight. The intent is
to allow users to build an archive "in pieces", and then compress all
of the entries at once with the Convert command. The conversion is
much faster if you take advantage of RAMdisk support.
A minor bug was detected in our handling of date/time stamps which
occasionally resulted in stamping an archive with the wrong date and
time. This has been corrected.
ARC Page 24
______________________ CHANGES IN VERSION 5.0
Several users of ARC have written us to suggest that we should put an
order form in the documentation. It seems that several types of
organizations require something like that or they cannot pay no matter
how much they'd like to. While doing that, we also went over the
documentation from top to bottom and "slicked it up". It's now a bit
more of an actual manual. We think you'll appreciate the table of
contents as well; we sure do!
The Move command used to delete the files as it went. It now waits
until it is finished updating the archive, and deletes them all at
did once. (You did know that Move is just an Add where the file gets
deleted, didn't you?) This, along with the changes made in version
4.5, means that it is now much safer to interrupt ARC while it is
working.
The Print command no longer prints the name of each file. Instead, it
prints a formfeed after each file.
The Run command now supports BASICA programs. Also, the filename
extension is no longer required on the Run command.
The Garble option was added. It provides a convenient means of low
level data security for the casual user. Use it sparingly, if at all.
ARC no longer tests for the presence of $ARCTEMP.CRN before creating a
new one. If you interrupt ARC a lot, you'll find this much more
convenient. If you happen to have a file named $ARCTEMP.CRN which you
want to keep, too bad.
Improved error recovery was added when reading an archive. ARC now
has a good chance of recovering the data from a corrupted archive (the
corrupted entry is still lost, of course).
Path support has been added for all commands, though it doesn't do
anything on most of them. For example, there isn't much we can do
with a path in the List command. But many users will be glad to know
that a path can be used when extracting a file, and specifies where
the file is to be placed.
Support for the TEMP environment string was added. If ARC doesn't
find an environment string named ARCTEMP, then it looks for one named
TEMP to use instead. Several packages already use the TEMP string for
exactly this purpose. With any luck, maybe we can get a standard
going.
ARC Page 25
ARC is now using a different variation of Lempel-Zev coding, courtesy
of Kent Williams, who found it on USENET and adapted it to the IBM PC.
The new method differs from the old in several respects. The most
significant differences are:
1) Where our previous implementation used a fixed code size of twelve
bits, the new one starts with a code size of nine bits and
increases it as it needs to.
2) The earlier method tended to "choke" on large files when its string
table filled up. The new method has a rather ingenious scheme its
adaptive reset authors call adaptive reset. When it notices that its string table
has filled, and its compression ratio is starting to suffer, it
clears the table and starts defining new strings.
Our benchmarks show an improvement in compression on the order of 10%
when crunching is used. Additionally, ARC 5.0 is on the order of 23%
faster at adding a file when crunching is used, or 13% faster when
squeezing is used. Extracting a file crunched with the new method is
27% faster than it is with the old method. Extraction of any other
type of file (including those crunched with the older method) is no
faster than before. These figures are based on our own benchmark
tests; your results may vary.
The previous implementation of Lempel-Zev coding is no longer used to
pack files. The "V" (Verbose listing) command distinguishes between
the two by referring to the older method as "crunched" (with a lower-
case "c"), and the newer method as "Crunched" (with a capital "C").
ARC 5.0 can still read archives created by earlier versions of ARC,
but once again it creates archives which older versions cannot read.
______________________ CHANGES IN VERSION 5.1
Rick Moore discovered that ARC was occasionally adding an archive to
itself. This would only happen when the archive is in the same
directory as the files being added, and its name comes last. This bug
has been fixed, though it is still possible to fool ARC into adding an
archive to itself by getting tricky with path names.
Dana Montgomery found the upper limit on how many files can be added
to an archive. There's always been an upper limit, but it depends on
memory, and used to be larger than anyone could possibly want (knock
on wood). However, the added memory requirements in version 5.0
lowered this limit into the realm of possibility. It's somewhere
around 500 files, though odd things may happen before then, depending
on how the heap gets fragmented. At any rate, ARC now tries to detect
the error and print a meaningful error message.
We've also introduced a new packaging method for ARC and its documen-
tation, since we are in the unique position of being unable to use ARC
for this purpose. We've created a program called ARC51.COM which,
when executed, attempts to create the ARC program and manual. You
must be in the same directory as ARC51.COM when you run it.
ARC Page 26
PROGRAM HISTORY AND CREDITS PROGRAM HISTORY AND CREDITS
In its short life thus far, ARC has astounded us with its popularity.
We first wrote it in March of 1985 because we wanted an archive
utility that used a distributive directory approach, since this has
certain advantages over the more popular central directory approach.
We added automatic squeezing in version 2 at the prompting of a
friend. In version 2.1 we added the code to test for the best
compression method. Now (in October of 1985) we find that our humble
little program has spread across the country, and seems to have become
a new institution.
We are thankful for the support and appreciation we have received. We
hope that you find this program of use.
If we have achieved greatness, it is because we have stood upon the
shoulders of giants. Nothing is created as a thing unto itself, and
ARC is no exception. Therefore, we would like to give credit to the
following people, without whose efforts ARC could not exist:
Brian W. Kernighan and P. J. Plauger, whose book "Software Tools"
provided many of the ideas behind the distributive directory approach
used by ARC.
Dick Greenlaw, who wrote the public domain SQ and USQ programs, in
which the Huffman squeezing algorithm was first developed.
Robert J. Beilstein, who adapted SQ and USQ to Computer Innovations
C86 (the language we use), thus providing us with important parts of
our squeezing logic.
Kent Williams, who graciously allowed us to use his LZWCOM and LZWUNC
programs as a basis for our Lempel-Zev compression logic, and who
continues to make valuable contributions.
David Schwaderer, whose article in the April 1985 issue of PC Tech
Journal provided us with the logic for calculating the CRC 16 bit
polynomial.
Terry A. Welch, whose article "A Technique for High Performance Data
Compression", IEEE Computer Vol 17 No 6 (June 1984) seems to have
started all the research on Lempel-Zev coding.
Spencer W. Thomas, Jim McKie, Steve Davies, Ken Turkowski, James A.
Woods, and Joe Orost, who are the authors of the UNIX compress
utility.
And many, many others whom we could not identify.
ARC Page 27
SITE LICENSE SITE LICENSE
Corporate users may wish to obtain a site license for the use of ARC.
Please use the order form in this manual to order a site license.
Site licenses are granted as of when we receive your payment. License
fees vary depending on the number of computers on which ARC will be
used, as follows:
1 to 9 copies $35 each
10 to 24 copies $25 each
25 to 49 copies $20 each
50 to 99 copies $15 each
over 99 copies $1500 one time fee
The following page is a site license agreement, which should be signed
and sent with your payment when ordering a commercial site license.
ARC Page 28
The use of ARC in a commercial environment or government organization
is granted under the following terms:
1. Payment of the license fee must be made to System Enhancement
Associates. The fee is based on the number of computers which
will be used to run ARC, as follows:
1 to 9 copies $35 each
10 to 24 copies $25 each
25 to 49 copies $20 each
50 to 99 copies $15 each
over 99 copies $1500 one time fee
2. You may use ARC on the number of computers included in the license
fee. If you have paid the fee for over 99 copies, then you may
use ARC on any number of computers within your organization.
3. You may make copies of the program, in its original, unmodified
form, without restriction. You may distribute these copies of
the program without restriction.
4. If these copies are distributed outside of your organization, you
have no obligation to control the use of those copies which are
outside of your organization.
5. You may make copies of the program documentation, in both its
printed form and machine readable form, without restriction.
6. You may use future versions of ARC under this license. The latest
version is available from System Enhancement Associates for a
small service charge.
7. You may NOT modify the program or charge a fee for copying or
distributing the program.
8. It is your responsibility to make the necessary copies and to
deliver them to the computers which they will be used on.
I agree to abide by the terms and conditions of this license.
_____________________________ __________________________
Signature Date
_____________________________
Name (please print or type)
_____________________________
Title
_____________________________
Company
ARC Page 29
ORDER FORM ORDER FORM
Check which items you wish to purchase:
(_) Noncommercial license for the use of ARC.
(_) Commercial license for the use of ARC on ___ computers (see
price schedule and terms on preceding page).
(_) Program disk and documentation (only on orders of $50 or
more).
(_) Program update subscription service (not more than five
updates, does not include trivial changes), $50/year.
(_) Payment of $_____ is enclosed (check or money order).
(_) Please charge $_____ to my (_) Visa or (_) MasterCard:
Card number: ______________________________
Expiration date: __________________________
_______________________________________________
Name
_______________________________________________
_______________________________________________
Address
______________________ ________ ____________
City State Zip
_______/_______
FidoNet address
Send this completed form to:
System Enhancement Associates
21 New Street
Wayne, NJ 07470
For program disk orders outside the U.S., please add an additional $5,
and enclose an international money order payable in U.S. currency.
For commercial site license orders, please enclose a signed copy of
the site license agreement.
ARC Page 30
