This character set was devised by the now extinct[2]Arab Standardization and Metrology Organization in 1982[2] to be the 7-bit standard to be used in Arabic-speaking countries. The design of this character set is derived[3] from the 7-bit ISO 646 (version of 1973) but with modifications suited for the Arabic language. In code points ranging from 0x41 to 0x72 (hexadecimal), Latin letters were replaced with Arabic letters. Punctuation marks which were identical in the Latin and Arabic scripts remained the same, but where they differed (comma, semicolon, question mark), the Latin ones were replaced by Arabic ones. Only nominal letters are encoded, no preshaped forms of the letters, so shaping processing is required for display. This character set is not bidirectional and was intended to be used in right to left writing. Therefore, symmetrical pairs of punctuation marks (( and ), < and >, [ and ], { and }) appear reversed () and (, > and <, ] and [, } and {).
There is a variant, sometimes named ASMO 449+[5] which adds the characters NBSP in 0x75, "ﹳ" in 0x76, "لآ" in 0x77, "لأ" in 0x78, "لإ" in 0x79 and "لا" in 0x7A.
Relationship with other character sets
ASMO 449 is a 7-bit character set. Although some encodings allocate this 7-bit character set in the upper part of the 8-bit character set, it should not be confused with ASMO 708. In the character sets that allocate ASMO 449 (or some variant of it) in the upper part of the 8-bit character set, the existence of apparently repeated characters is due to the fact that the characters in the lower part are for left-to-right script while the characters in the upper part are for right-to-left script. When ASMO 449 (or some variant of it) is allocated to the upper part of the 8-bit character set, it has Arabic digits.
Al-Arabi[5] adds the characters NBS in 0xF5, "-" in 0xF6, "÷" in 0xF7, "×" in 0xF8, "«" in 0xF9 and "»" in 0xFA, and replaces "ـ" with "`"; this character set is sometimes referred as Code Page 768 (not an official IBM code page).
DEC's DEC/8/ASMO[5] has the same repertoire and the same sequence of Arabic characters but dislocates them.
Apple's MacArabic adds French, German and Spanish characters in their typical code points from MacRoman, and adds letters for Persian and Urdu.
Apple's MacFarsi replaces the Arabic digits from MacArabic with Persian ones.
The Code Table 7[6] from MARC-8 allocates ASMO 449 in the lower part of the 8-bit character set and allocates the upper part with the Arabic Extension (ISO 11822 / IR 224).
Microsoft's Code page 709,[5] for MS-DOS, adds French and German characters in their typical code points from code page 437.
References
^Computing and the Qurʾān - Some caveats, 2007, Thomas Milo
