StuffIt X Format Options

Compression Method

Compression method allows you to select different compressors for use when adding files to a StuffIt X archive with compression. Method is passed to the compressor as a value between 0 and 6.

• Method 1: Method 1 provides compression that is optimized for speed of compression and decompression. It works by replacing a series of bytes with a reference to a previous occurrence of the same series of bytes.

• Method 2: Method 2 is optimized for the compression of binary files (such as applications) and also for fast decompression. Method 2 works in the same way as Method 1, except that it has a more exact way of representing the offsets and lengths, which makes it compress a little more, but at the cost of slower compression and decompression. Typically Method 2 will provide you with the best results when you’re compressing applications.

• Method 3: Method 3 provides the best trade off between compression/decompression speed and archive file size and works well on a variety of different file types. This compression method does a reversible sort on the data, which places like data closer together which makes it more compressible.

• Method 4: Method 4 provides compression that is primarily optimized for text. This compression method works by “predicting” what the next byte will be based on previous data. For example, if it is predicting the byte following “t” and “h”, it will give high probabilities to “e”, and “a”.

• Method 5: This compression method uses a file filter to determine which of the previous methods should be used to compress a file based on its file type.

• Method 6: This method breaks the file being compressed into small pieces and compresses each piece with methods 2 through 4. Whichever method produces the smallest output is used for that chunk of data. This makes it very slow but it generally produces the smallest possible files.

Level and Extent

Levels generally set “how hard” each method tries to compress.

In the matching algorithms (method 1 & 2), levels 1-9 generally correspond to Gzip's compression levels. The higher the number the harder it tries to find a match (more compression, but slower). Levels above 9 use a different, more exhaustive search for previous matches, which gets extra compression, but at the expense of speed. In the “prediction” algorithm, the level corresponds to how many previous bytes to use when making the prediction.

Extents generally set how much data is processed at a time.

Extents has a direct relationship to how much memory is used. In methods 1 & 2, the extent sets how far back to look for a match. In method 4, extent sets how much memory to used for storing the prediction information.

As you move the Extent slider, you will see an estimate of how much memory will be used for compression and decompression displayed. The StuffIt application is currently configured to cap compression settings so that the maximum amount of memory required to expand a StuffIt X archive is 64Mb.

Encryption

StuffIt X archives can be created with encryption. There are 4 compression methods supported:

• 1=RC4 - Supports up to 512bit key lengths.

• 2=DES - Supports up to 64bit key lengths

• 3=BlowFish - Supports up to 448bit key lengths

• 4=AES - Supports up to 256bit key lengths

When you use encryption through on of the options in the StuffIt application, RC4 will be used by default.

Text Encoding

StuffIt X archives can also be converted to ASCII text format. Three text encoding methods are available, Base64, Base 88, and Base 222. The levels of available text encoding determine how much of the full ACSII character set will be used to encode the data.The more characters used, the less size overhead will be imposed as a result of translating the binary data of the archive into text characters. When sending archives via E-mail, it is best to use Base64. This uses the fewest characters, but as a result is the most compatible. Base 222 is a good choice if files are being posted to a news group.

StuffIt X archives created with Text Encoding can only be opened as "Read Only" archives, meaning that you can browse their contents and extract files, but you cannot add new items, or delete existing ones.

Redundancy

StuffIt X archives can be created with Redundancy. Adding Redundancy information to an archive will increase its size, but its availability allows the engine to reconstruct data damaged as the result of bad media or transfer errors during the decode phase. You can change the level of error correction that is applied to an archive, the values are defined as the percentage of a block that can be recovered: 1/8, 1/16, 1/32, 1/64, and 1/128. Error correction is off by default.

StuffIt X archives created with Redundancy can only be opened as "Read Only" archives, meaning that you can browse their contents and extract files, but you cannot add new items, or delete existing ones.

Optimizers

When optimizers are turned on, StuffIt will look for specific types of files as they are being added to the archive, and always compress them with a compression method that is optimized specifically for that file type. Optimizers are on by default.

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