Among various character sets that are used for Hebrew characters on computers and the Internet, 1) Unicode / ISO 10646 (UCS (Universal Multiple-Octet Coded Character Set)), 2.1) ISO-8859-8-I ("Logical Hebrew"), 2.2) ISO-8859-8 ("Visual Hebrew") and 3) Windows-1255 ("Windows Hebrew") are probably the most widely used ones.
Unicode is a 16-bit coded character set covering most of the characters used in the major languages of the world, including Hebrew characters, so it makes it possible to mix Hebrew letters, vowel signs and cantillation marks as well as characters of other scripts. In many areas of computing it is mostly used in the form of UTF-8 (Unicode Transformation Format 8-bit Encoding Form). It is a 7-48 bit character encoding scheme of Unicode using an 8-bit base, and is compatible with ASCII, which is in its 7-bit format. Unicode, especially UTF-8, is becoming the de facto standard encoding not only for Hebrew but also other characters of the world.
ISO-8859-8(-I) is a 8-bit coded character set covering ASCII and Hebrew letters but not vowel signs and cantillation marks. Like Unicode, ISO-8859-8-I ("Logical Hebrew") supports the bidirectional algorithm, which enables the correct visual rendition of Hebrew characters encoded in a logical order. On the other hand, ISO-8859-8 ("Visual Hebrew") does not support it, so Hebrew characters are encoded in a reverse logical order so that they may be visually rendered from right to left. It used to be used for browsers and other programs not supporting the bidirectional algorithm, and is still used as a legacy of the past, especially for web documents. One of its shortcomings is that the maximam number of characters on a single line must be predetermined, so if the size of fonts and display is altered, lines and the order of characters are messed up, and it is impossible to copy and paste Hebrew text strings encoded in it. Furthermore, more and more programs, including browsers, support the bidirectional algorithm. Therefore, it is losing its raison d'être.
Windows-1255 ("Windows Hebrew") is a proprietary 8-bit coded character set (or "code page") by Microsoft. It is identical to ISO-8859-8(-I) in positions that are assigned to ASCII and Hebrew letters, but it covers vowel signs in positions that are reserved for control characters in ISO-8859-8(-I). It is recommended to avoid using this character set.