Code page 437

Code page 437 is the character set of the original IBM PC (personal computer), or MS-DOS. It is also known as CP437, OEM 437,^[1] PC-8,^[2] or MS-DOS Latin US.^[3] The set includes ASCII codes 32–126, extended codes for accented letters (diacritics), some Greek letters, icons, and line-drawing symbols. It is sometimes referred to as the "OEM font" or "high ASCII", or as "extended ASCII"^[2] (one of many mutually incompatible ASCII extensions).

In a strict sense, this character set was not conceived as a code page; it was simply the graphical glyph repertoire available in the original IBM PC. This character set remains the primary font in the core of any EGA and VGA-compatible graphics card. Text shown when a PC reboots, before any other font can be loaded from a storage medium, typically is rendered with this "Code Page".^[4] Many file formats developed at the time of the IBM PC, such as .nfo, define this as the default encoding.

Display adapters

The code page stored in ROM is also called the hardware code page. In Western PCs it typically defaults to code page 437, but various Eastern European PCs used a number of other code pages as their hardware code page, sometimes user-selectable via jumpers or CMOS setup. Arabic and Hebrew PCs and printers even supported multiple software-switchable hardware code pages, also named font pages.

The original IBM PC contained this font as a 9×14 pixels-per-character font stored in the ROM of the IBM Monochrome Display Adapter (MDA) and an 8×8 pixels-per-character font of the Color Graphics Adapter (CGA) cards. The IBM Enhanced Graphics Adapter (EGA) contained an 8×14 pixels-per-character version, and the VGA contained a 9×16 version.

All these display adapters have text modes in which each character cell contains an 8-bit character code point (see details), giving 256 possible values for graphic characters. All 256 codes were assigned a graphical character in ROM, including the codes from 0 to 31 that were reserved in ASCII for non-graphical control characters.

Alt Codes

A legacy of code page 437 and other DOS codepages is the set of number combinations used in Windows Alt keycodes introduced in the first versions of MS-DOS. The user could enter a character by holding down the Alt key and entering the three-digit decimal Alt keycode on the numpad. When Microsoft switched to more standard character sets (such as CP1252 and later Unicode) in Windows, so many users had memorized the numbers used by their DOS codepage that Microsoft chose to retain the original codes (they added the ability to type a code in the current character set by typing the numpad 0 before the digits).

Characters

The following tables show code page 437. Each character is shown with its equivalent Unicode code point and its decimal code point. See also the notes below as there are multiple equivalent Unicode characters for some code points. The decimal codes are also known as Alt codes.

Although the ROM provides a graphic for all 256 different possible 8-bit codes, some APIs that ostensibly support code page 437 will not print some or all of these code points, in particular the range 1-31 and the code at 127.^[5] Instead they will interpret them as control characters. For instance the BIOS on the original IBM PC has a character-output command that would interpret the codes for CR, LF, BS, and some others. Code 26 (^Z) could not be stored in MSDOS text files as it indicated end of file. Many printers were also unable to print these characters.

Implementers of translation to Unicode should note that these codes do not have a unique, single Unicode equivalent and the correct choice depends upon context:

• 0 and 255 (FF_hex) both draw a blank space, as does 32 (20_hex). The use of 255 for U+00A0 Non-breaking space (NBSP) has some precedent in word processors designed for the IBM PC.
• 225 (E1_hex) is both the German sharp S (U+00DF, ß) and the Greek lowercase beta (U+03B2, β).
• 227 (E3_hex) is the Greek lowercase pi (U+03C0, π), but early fonts such as Terminal use a variant of pi that is ambiguous in case, and therefore can be used for the Greek capital pi (U+03A0, Π) or the n-ary product sign (U+220F, ∏).
• 228 (E4_hex) is both the n-ary summation sign (U+2211, ∑) and the Greek uppercase sigma (U+03A3, Σ).
• 230 (E6_hex) is both the micro sign (U+00B5, µ) and the Greek lowercase mu (U+03BC, μ).
• 234 (EA_hex) is both the ohm sign (U+2126, Ω) and the Greek uppercase omega (U+03A9, Ω). (Unicode considers the ohm sign to be equivalent to uppercase omega, and suggests that the latter be used in both contexts.^[7]).
• 235 (EB_hex) is the Greek lowercase delta (U+03B4, δ), but it has also been used as a surrogate for the Icelandic lowercase eth (U+00F0, ð) and the partial derivative sign (U+2202, ∂).
• 237 (ED_hex) is supposed to be used as Greek lowercase phi, but is mainly used as the empty set sign (U+2205, ∅) and was also used as the Greek phi symbol in italics (U+03D5, Φ) to name angles, diameter sign (U+2300, ⌀), and as a surrogate for the Latin lowercase O with stroke (U+00F8, ø).
• 238 (EE_hex) is both the Greek lowercase epsilon (U+03B5, ε) and the element-of sign (U+2208, ∈). Later it was often used for the euro sign (U+20AC, €).

History

The repertoire of code page 437 was taken from the character set of Wang word-processing machines, according to Bill Gates in an interview with Gates and Paul Allen that appeared in the 2 October 1995 edition of Fortune Magazine:

"... We were also fascinated by dedicated word processors from Wang, because we believed that general-purpose machines could do that just as well. That's why, when it came time to design the keyboard for the IBM PC, we put the funny Wang character set into the machine—you know, smiley faces and boxes and triangles and stuff. We were thinking we'd like to do a clone of Wang word-processing software someday."

The selection of graphic characters has some internal logic:

• Table rows 0 and 1, codes 0 to 31 (00_hex to 1F_hex), are assorted dingbats (complementary and decorative characters). The isolated character 127 (7F_hex) also belongs to this group.
• Table rows 2 to 7 (except character 127, 7F_hex), codes 32 to 126 (20_hex to 7E_hex), are the standard ASCII printable characters.
• Table rows 8 to 10 (8_hex to A_hex), codes 128 to 175 (80_hex to AF_hex), are a selection of international text characters.
• Table rows 11 to 13 (B_hex to D_hex), codes 176 to 223 (B0_hex to DF_hex), are box drawing and block characters. This block is arranged so that characters 192 to 223 (C0_hex to DF_hex) contain all the right arms and right-filled areas. The original IBM PC MDA display adapter stored the code page 437 character glyphs as bitmaps eight pixels wide, but for visual enhancement displayed them every nine pixels on screen. This range of characters had the eighth pixel column duplicated by special hardware circuitry,^[8] thus filling in gaps in lines and filled areas.
• Table rows 14 and 15 (E_hex and F_hex), codes 224 to 255 (E0_hex to FF_hex) are devoted to mathematical symbols, where the first twelve are a selection of Greek letters commonly used in physics. Characters 244 (F4_hex) and 245 (F5_hex) are the upper and lower portion of an italic long S, the symbol used as the integral sign (∫), and they can be extended with the character 179 (B3_hex), the vertical line of the box drawing block. Character 244 could also be used as a surrogate for the ſ character. Characters 249 (F9_hex) and 250 (FA_hex) are almost indistinguishable: the first is slightly larger than the second, which resembles the typographic middle dot (·). The character 255 (FF_hex) is merely blank, and acts as a kind of non-breaking space in order to arrange math formulae.

Most fonts for Microsoft Windows include the special graphic characters at the Unicode indexes shown, as they are part of the WGL4 set that Microsoft encourages font designers to support. (The monospaced raster font family Terminal was an early font that replicated all code page 437 characters, at least at some resolutions.) To draw these characters directly from these code points, a Microsoft Windows font called MS Linedraw^[9] replicates all of the code page 437 characters, thus providing one way to display DOS text on a modern Windows machine as it was shown in DOS, with limitations.^[10]

Internationalization

Code page 437 has a series of international characters, mainly values 128 to 175 (80_hex to AF_hex). However, it lacks several characters important to many Western languages:

• Spanish (Á, Í, Ó, Ú), French (À, Â, È, Ê, Ë, Ì, Î, Ï, Ô, Œ, œ, Ù, Û), Portuguese (Á, À, Â, Ã, ã, Ê, Í, Ó, Ô, Õ, õ, Ú), and Catalan (À, È, Í, Ï, Ò, Ó, Ú).
• German sharp S (ß) shares its code point with the beta symbol (β), which is acceptable at the low resolution on the original IBM CGA hardware, but unacceptable at higher resolutions. Most newer glyph sets for code page 437, including those built into the IBM EGA and VGA graphics cards, prefer the German sharp S shape for this character.
• Scandinavian lacks slashed-o 'Ø' and 'ø'. Character number 237 (ED_hex), the empty set symbol, could be used as a surrogate, but its spacing is awkward for display within a word. To compensate, the Danish/Norwegian and Icelandic code pages (865 and 861), replaced cent mark (¢) with 'ø' and yen (¥) with 'Ø'.
• Most Greek alphabet symbols were omitted, beyond the basic math symbols. (They were included in the Greek-language code pages 737 and 869.)

Along with the cent (¢), pound sterling (£) and yen/yuan (¥) currency symbols, it has a couple of former European currency symbols: the florin (ƒ, Netherlands) and the peseta (₧, Spain). The presence of the last is unusual, since the Spanish peseta was never an internationally relevant currency, and also never had a symbol of its own; it was simply abbreviated as "Pt", "Pta", "Pts", or "Ptas". Spanish models of the IBM electric typewriter, however, also had a single position devoted to it.

Later MS-DOS character sets, such as code page 850 (DOS Latin-1), code page 852 (DOS Central-European) and code page 737 (DOS Greek), filled the gaps for international use with some compatibility with code page 437 by retaining the single and double box-drawing characters, while discarding the mixed ones (e.g. horizontal double/vertical single). All code page 437 characters have similar glyphs in Unicode and in Microsoft's WGL4 character set, and therefore are available in most fonts in Microsoft Windows, and also in the default VGA font of the Linux kernel, and the ISO 10646 fonts for X11.

See also

• Alt codes
• ANSI
• ANSI art
• ASCII
• ASCII art
• .nfo file format, which uses CP437
• Semi graphical characters
• Western Latin character sets (computing)
• Terminal (typeface)
• Nibble
• Dwarf Fortress

References

1. ↑ "OEM 437". Go Global Developer Center. Microsoft. Retrieved 22 Sep 2011. 
2. 1 2 "OEM font". Encyclopedia. PCmag.com. Retrieved 15 Nov 2011. 
3. ↑ "Code Page 437 MS-DOS Latin US". Developing International Software. Microsoft. Retrieved 14 Nov 2011. 
4. ↑ Systems available in Eastern European, Arabic, and Asian countries often use a different set. The designation "OEM", for "original equipment manufacturer", indicates that the "native" hardware character set supplied in ROM could be changed by the manufacturer to meet different markets.
5. ↑ "00437". Code pages by CPGID. IBM. Retrieved 14 Nov 2011. 
6. ↑ "cp437_DOSLatinUS to Unicode table" (TXT). The Unicode Consortium. Retrieved 14 Nov 2011. 
7. ↑ The Unicode Consortium, The Unicode Standard 4.0, Chapter 7, "European Alphabetic Scripts", p176. PDF version
8. ↑ Richard Wilton, Programmer's Guide to PC & PS/2 Video Systems, 1987, Microsoft Press.
9. ↑ Staff (2012). "MS LineDraw - Version 2.00". Microsoft. Microsoft Corporation. Retrieved 1 July 2012. 
10. ↑ Staff (22 January 2007). WD97 "WD97: MS LineDraw Font Not Usable in Word" Check |url= value (help). Microsoft. Microsoft. Retrieved 1 July 2012. 

External links

• IBM Code Page 437 reference chart
• IBM PC memory-mapped video graphics to Unicode on official Unicode site

Character encodings Character sets Early telecommunications ASCII ISO/IEC 646 ISO/IEC 6937 T.61 BCD Baudot code Morse code (Telegraph code) Special telegraphy codes: Non-Latin, Chinese, Cyrillic ISO/IEC 8859 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 -14 -15 -16 Bibliographic use ANSEL ISO 5426 / 5426-2 / 5427 / 5428 / 6438 / 6861 / 6862 / 10585 / 10586 / 10754 / 11822 MARC-8 National standards ArmSCII CNS 11643 GOST 10859 GB 18030 HKSCS ISCII JIS X 0201 JIS X 0208 JIS X 0212 JIS X 0213 KPS 9566 KS X 1001 PASCII SI 960 TIS-620 TSCII VISCII YUSCII EUC CN JP KR TW ISO/IEC 2022 CN JP KR CCCII MacOS codepages ("scripts") Arabic CentralEurRoman ChineseSimp / EUC-CN ChineseTrad / Big5 Croatian Cyrillic Devanagari Dingbats Farsi Greek Gujarati Gurmukhi Hebrew Icelandic Japanese / ShiftJIS Korean / EUC-KR Roman Romanian Symbol Thai / TIS-620 Turkish Ukrainian DOS codepages 111 112 113 151 161 162 163 164 165 220 300 301 367 371 437 449 620 667 668 708 709 710 711 720 737 770 771 772 773 774 775 776 777 778 790 806 808 813 819 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 872 874 876 877 878 881 882 883 884 885 891 895 896 897 898 899 900 901 902 903 904 906 907 909 910 911 912 913 914 915 916 919 920 921 922 923 925 926 927 928 932 934 936 938 941 942 943 944 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 971 991 1004 1006 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1023 1029 1034 1036 1038 1039 1040 1041 1042 1043 1044 1046 1086 1088 1089 1090 1092 1093 1098 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1111 1114 1115 1116 1117 1118 1119 1124 1125 1126 1127 1129 1131 1133 1139 1161 1162 1163 1167 1168 1169 1174 1270 1275 1276 1277 1280 1281 1282 1283 1284 1285 1286 1287 1288 1350 1351 1361 1362 1363 1373 Kamenický Mazovia MIK Iran System Windows codepages 874 / TIS-620 932 / Shift JIS 936 / GBK 949 / EUC-KR 950 / Big5 1200 / UTF-16 (Little Endian) 1201 / UTF-16 (Big Endian) 1250 1251 1252 1253 1254 1255 1256 1257 1258 54936 / GB18030 EBCDIC codepages 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 29 30 31 32 33 34 35 36 37/1140 38 39 40 251 252 254 256 257 258 259 260 264 273/1141 274 275 276 277/1142 278/1143 280/1144 281 282 283 284/1145 285/1146 286 287 288 289 290 293 297/1147 298 310 320 321 322 330 351 361 363 382 383 384 385 386 387 388 389 390 391 392 393 394 395 410 420/16804 421 423 424/12712 425 435 500/1148 803 829 833 834 835 836 837 838/1160 839 870/1153 871/1149 875/9067 880 881 882 883 884 885 886 887 888 889 890 892 893 905 918 924 930/1390 931 933/1364 935/1388 937/1371 939/1399 1001 1002 1003 1005 1007 1024 1025/1154 1026/1155 1027 1028 1030 1031 1032 1033 1037 1047/924 1068 1069 1070 1071 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1087 1091 1097 1110 1112/1156 1113 1122/1157 1123/1158 1130/1164 1132 1136 1137 1150 1151 1152 1159 1165 1166 1278 1303 1364 JEF KEIS Platform specific ATASCII CDC display code DEC-MCS DEC Radix-50 ELWRO-Junior Fieldata GSM 03.38 HP roman8 PETSCII TI calculator character sets WISCII ZX80 character set ZX Spectrum character set Unicode / ISO/IEC 10646 UTF-8 UTF-16/UCS-2 UTF-32/UCS-4 UTF-7 UTF-1 UTF-EBCDIC GB 18030 SCSU BOCU-1 Miscellaneous codepages APL Cork HZ JOHAB KOI8 TRON Related topics control character (C0 C1) CCSID Character encodings in HTML charset detection Han unification ISO 6429/IEC 6429/ANSI X3.64 mojibake