#Express zip threat softwareThis header takes up some space, so reduces the efficiency of the compression, but it allows the compression software to use any type of character-set that it likes, making it useable for any file. So what I can do is to include a special header in the file, a small piece of data that contains the details of the encoding used, in this case it will mention that each character uses 5 bits and then has a list of all the characters that are used. Now a file like this can only be interpreted correctly if the software on the other end knows it's dealing with a file that uses 5 bits to encode a lowercase letter. #Express zip threat fullSo for the first character, I don't use the full byte, but rather just the first 5 bits and for the next character, I use 3 remaining bits of the first byte and 2 bits from the next byte, etc. If I know that a file only contains lowercase letters, I only need 26 different characters, which can be covered with just 5 out of the 8 bits that make up a byte. Using standard ASCII encoding, 1 character uses 1 byte of space, but this 1 byte allows for 256 different characters to be expressed. Note that this algorithm is very simplistic and could still be improved.Īnother technique that can be used is reducing the size of the alphabet. $=Reddit!I'm going to write $ \5 times (5$) and post it on $. Applying our compression algorithm, we get: I'm going to write Reddit 5 times (RedditRedditRedditRedditReddit) and post it on Reddit. We use the \ to indicate that the following character has no special meaning and should be interpreted literally. We use the format "X=word" at the start of the text to define a substitution of "word" by symbol "X", with the actual text starting with a !. Lets use both of the previous concepts (replacement of repeated data in a sequence by a number and a single instance of that data and replacement of freqeuntly occurring data by a special symbol and a "dictionary" at the start of the file). In order to ensure that the decompression software knows what's going on, the file format could be such that it first includes a list of these substitutions, followed by a specific symbol (or combination thereof) that marks the actual content.Ī practical example. Suppose a piece of text contains many instances of a certain word, then the software could replace that word by a single character/symbol. Next up a compression tool might replace recurring pieces of data by a symbol that takes up considerably less space. In some special cases, the filesize actually increases due to the rules I introduced to properly represent numbers and slashes. In certain cases, where the file doesn't contain many numbers or slashes, the size of the file can be reduced by this shorthand notation. If I know that files of this type rarely contain anything other than letters, I could replace this string by "20a" and program my software to read this as an instruction to create a string of 20 a's.īut what happens if I want to use the same function for something that does contain a number? Well, I could decide that any number that is to be interpreted literally, rather than as part of an instruction is preceded by a -symbol (and then add the special case of using \ whenever I want to represent a single ). This is 20 characters of data (or 20 bytes using basic ASCII encoding). Suppose I have a file that contains the string "aaaaaaaaaaaaaaaaaaaa" (w/o quotes). It's best explained with a simplified example. Zip/compress to reduce file size for email transmission or save hard drive disc space when archiving.Compression is a way to more efficiently store data. Easily create, edit, manage and extract zipped files and folders on OS X. #Express zip threat mac* Simple but powerful user interface with easy-to-use drag and drop functionalityĮxpress Zip Mac File Compression Software is easy-to-use. * Burn archived files to CD/DVD for long term backup * Quickly zip common folders with the Express menu * Convert archives to zip from other formats * Open and extract other archives including rar, iso, cab, 7z, tar and more Fast and efficient file zipping and unzipping lets you create zip files of your important documents, images, music and more to save disk space, email or burn to CD. #Express zip threat archiveCompress files to reduce size for email transmission or archive data using less disk space when backing up information. An archiving and file compression tool to easily create, edit, manage and extract zipped files and folders. Express Zip Mac File Compression Software.
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