Code page 437


Code page 437
Code page 437, as rendered by the IBM PC using a VGA adapter.

IBM PC or MS-DOS code page 437, often abbreviated CP437 and also known as DOS-US, OEM-US or sometimes misleadingly referred to as the OEM font, High ASCII or Extended ASCII,[1][2] is the character set of the original IBM PC.

In a strict sense, this character set was not born as a code page but was simply the graphical glyph repertoire available in the 9 by 14 pixels-per-character font of the IBM Monochrome Display Adapter (MDA) and the 8 by 8 pixels-per-character font of the Color Graphics Adapter (CGA) cards of the original IBM PC. The ROM of the IBM Enhanced Graphics Adapter (EGA) has an 8 by 14 pixels-per-character version and the VGA adapter expanded the character cell to 9 by 16 for the finer VGA resolution. Today, the character set is still the primary font in the core of any EGA and VGA compatible graphic card; i.e. the text you can see on screen when a PC reboots, before any other font can be loaded from a storage medium, is rendered with this "code page".

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. This way, beyond the original ASCII graphical character set (values 32dec to 126dec, 95 in total), the implementors put in ROM a handful of miscellaneous characters even for the range 0dec to 31dec, reserved in ASCII for control (non graphical) purposes.

The code page has two main uses: as an information interchange code (through files and telecom), in which the values 0dec to 127dec plays the same role as in ASCII plus the international text characters 128dec to 175dec (see the table below), and as a graphical resource for screen and printers (by merely writing in the video RAM character cell/sending through line the appropriate code), in which the full range can be used to build fine presentations.

Contents

Characters

The following is a table representing CP437 using equivalent Unicode characters (see notes below as there are multiple equivalent Unicode characters for some cells).

For many uses, the codes in the range 0dec to 31dec and the code 127dec will not produce these symbols. Some (or all) of them will be interpreted as ASCII control characters. For instance sending the code 13dec to a terminal or printer is very likely to produce a carriage return and not an eighth-note symbol.

Most fonts for Microsoft Windows include these glyphs 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 CP437 characters, at least at some resolutions). To draw these glyphs directly from these code values, a Microsoft Windows font called MS Linedraw[3] replicates all of the CP437 characters, thus providing one way to display DOS text on a contemporary Windows machine as it was shown in DOS, with limitations.[4]

CP437
−0 −1 −2 −3 −4 −5 −6 −7 −8 −9 −A −B −C −D −E −F
 
0−
 
NUL
0000
0

263A
1

263B
2

2665
3

2666
4

2663
5

2660
6

2022
7

25D8
8

25CB
9

25D9
10

2642
11

2640
12

266A
13

266B
14

263C
15
 
1−
 

25BA
16

25C4
17

2195
18

203C
19

00B6
20
§
00A7
21

25AC
22

21A8
23

2191
24

2193
25

2192
26

2190
27

221F
28

2194
29

25B2
30

25BC
31
 
2−
 
SP
0020
32
!
0021
33
"
0022
34
#
0023
35
$
0024
36
%
0025
37
&
0026
38
'
0027
39
(
0028
40
)
0029
41
*
002A
42
+
002B
43
,
002C
44
-
002D
45
.
002E
46
/
002F
47
 
3−
 
0
0030
48
1
0031
49
2
0032
50
3
0033
51
4
0034
52
5
0035
53
6
0036
54
7
0037
55
8
0038
56
9
0039
57
:
003A
58
;
003B
59
<
003C
60
=
003D
61
>
003E
62
?
003F
63
 
4−
 
@
0040
64
A
0041
65
B
0042
66
C
0043
67
D
0044
68
E
0045
69
F
0046
70
G
0047
71
H
0048
72
I
0049
73
J
004A
74
K
004B
75
L
004C
76
M
004D
77
N
004E
78
O
004F
79
 
5−
 
P
0050
80
Q
0051
81
R
0052
82
S
0053
83
T
0054
84
U
0055
85
V
0056
86
W
0057
87
X
0058
88
Y
0059
89
Z
005A
90
[
005B
91
\
005C
92
]
005D
93
^
005E
94
_
005F
95
 
6−
 
`
0060
96
a
0061
97
b
0062
98
c
0063
99
d
0064
100
e
0065
101
f
0066
102
g
0067
103
h
0068
104
i
0069
105
j
006A
106
k
006B
107
l
006C
108
m
006D
109
n
006E
110
o
006F
111
 
7−
 
p
0070
112
q
0071
113
r
0072
114
s
0073
115
t
0074
116
u
0075
117
v
0076
118
w
0077
119
x
0078
120
y
0079
121
z
007A
122
{
007B
123
|
007C
124
}
007D
125
~
007E
126

2302
127
 
8−
 
Ç
00C7
128
ü
00FC
129
é
00E9
130
â
00E2
131
ä
00E4
132
à
00E0
133
å
00E5
134
ç
00E7
135
ê
00EA
136
ë
00EB
137
è
00E8
138
ï
00EF
139
î
00EE
140
ì
00EC
141
Ä
00C4
142
Å
00C5
143
 
9−
 
É
00C9
144
æ
00E6
145
Æ
00C6
146
ô
00F4
147
ö
00F6
148
ò
00F2
149
û
00FB
150
ù
00F9
151
ÿ
00FF
152
Ö
00D6
153
Ü
00DC
154
¢
00A2
155
£
00A3
156
¥
00A5
157

20A7
158
ƒ
0192
159
 
A−
 
á
00E1
160
í
00ED
161
ó
00F3
162
ú
00FA
163
ñ
00F1
164
Ñ
00D1
165
ª
00AA
166
º
00BA
167
¿
00BF
168

2310
169
¬
00AC
170
½
00BD
171
¼
00BC
172
¡
00A1
173
«
00AB
174
»
00BB
175
 
B−
 

2591
176

2592
177

2593
178

2502
179

2524
180

2561
181

2562
182

2556
183

2555
184

2563
185

2551
186

2557
187

255D
188

255C
189

255B
190

2510
191
 
C−
 

2514
192

2534
193

252C
194

251C
195

2500
196

253C
197

255E
198

255F
199

255A
200

2554
201

2569
202

2566
203

2560
204

2550
205

256C
206

2567
207
 
D−
 

2568
208

2564
209

2565
210

2559
211

2558
212

2552
213

2553
214

256B
215

256A
216

2518
217

250C
218

2588
219

2584
220

258C
221

2590
222

2580
223
 
E−
 
α
03B1
224
ß
00DF
225
Γ
0393
226
π
03C0
227
Σ
03A3
228
σ
03C3
229
µ
00B5
230
τ
03C4
231
Φ
03A6
232
Θ
0398
233
Ω
03A9
234
δ
03B4
235

221E
236
φ
03C6
237
ε
03B5
238

2229
239
 
F−
 

2261
240
±
00B1
241

2265
242

2264
243

2320
244

2321
245
÷
00F7
246

2248
247
°
00B0
248

2219
249
·
00B7
250

221A
251

207F
252
²
00B2
253

25A0
254
NBSP
00A0
255
−0 −1 −2 −3 −4 −5 −6 −7 −8 −9 −A −B −C −D −E −F

Along with the characters in the range 0dec to 31dec (00hex to 1Fhex), which can be interpreted as ASCII controls as well as graphical dingbats, some characters have overloaded meanings. 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 255dec (FFhex) both draw a blank space, as does 32dec (20hex). The use of 255dec for U+00A0 Non-breaking space (NBSP) has some precedent in word processors designed for the IBM PC.
  • 225dec (E1hex) is both the German sharp S (U+00DF, ß) and the Greek lowercase beta (U+03B2, β).
  • 227dec (E3hex) 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, ∏).
  • 228dec (E4hex) is both the n-ary summation sign (U+2211, ∑) and the Greek uppercase sigma (U+03A3, Σ).
  • 230dec (E6hex) is both the micro sign (U+00B5, µ) and the Greek lowercase mu (U+03BC, μ).
  • 234dec (EAhex) 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.[5]).
  • 235dec (EBhex) 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, ∂).
  • 237dec (EDhex) is supposed to be used as Greek lowercase phi, but is mainly used as the empty set sign (U+2205, \varnothing) and was also used as the Greek phi symbol in italics (U+03D5, \phi\,\!) to name angles, diameter sign (U+2300, \varnothing), and as a surrogate for the Latin lowercase O with stroke (U+00F8, ø).
  • 238dec (EEhex) 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, €).

Entry on keyboards

In DOS and Windows, most characters from the currently active DOS code page can be inserted by holding down the Alt key and entering the character's three-digit decimal code on the numpad. This technique is called Windows Alt keycodes. One can find out which DOS code page is currently active by issuing the DOS command mode con or chcp.

Difference from ASCII

CP437 is based on ASCII, with the following modifications:

  • Codes from the C0 control range (00hex to 1Fhex) and ASCII DEL (7Fhex) can assume their original function as control characters, but also function as graphic symbols when displayed in text mode from the screen buffer. For example, DEL and most of the C0 control codes are displayed graphically in a screen editor like MS-DOS Editor or when written to the screen via the DOS type command. The graphics include smiling faces, card suits, and musical notes. Code 127dec (7Fhex), DEL, shows as a "house". This behavior is not specific to CP437, but shared by all DOS code pages and so-called Windows OEM code pages, which generally resemble CP437.
  • The high-bit range, 128dec to 255dec (80hex to FFhex), is mapped to various symbols: a few European characters (accented Latin letters, etc.) in no particular order and not sufficient for representation of most Western European languages; box drawing characters; mathematical symbols; and a few Greek letters commonly used in mathematics and physics.

The repertoire of CP437 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, often called bizarre,[citation needed] has some internal logic:

  • Table rows 0 and 1, codes 0dec to 31dec (00hex to 1Fhex), are assorted dingbats (complementary and decorative characters). The isolated character 127dec (7Fhex) also belongs to this group.
  • Table rows 2 to 7 (except character 127dec, 7Fhex), codes 32dec to 126dec (20hex to 7Ehex), are the standard ASCII printable characters.
  • Table rows 8dec to 10dec (8hex to Ahex), codes 128dec to 175dec (80hex to AFhex), are a selection of international text characters.
  • Table rows 11dec to 13dec (Bhex to Dhex), codes 176dec to 223dec (B0hex to DFhex), are box drawing and block characters. This block is arranged so that characters 192dec to 223dec (C0hex to DFhex) of the rows 12dec and 13dec (Chex and Dhex) have all right arms (except 217dec, D9hex) or right filled areas (except 221dec, DDhex), and this is due to the following technical reason:[6] the original IBM PC MDA display adapter stored the CP437 character glyphs as bitmaps eight pixels wide, but for visual enhancement displayed them every nine pixels on screen (eight plus an additional gap). Thus characters with connections at their right edge had to duplicate their eighth pixels to avoid visual interruptions in the designs built up with them. This pixel extension is done by special hardware circuitry, and only this character subset is affected.
  • Table rows 14dec and 15dec (Ehex and Fhex), codes 224dec to 255dec (E0hex to FFhex) are devoted to mathematical symbols, where the first twelve are a selection of Greek letters commonly used in physics. Characters 244dec (F4hex) and 245dec (F5hex) 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 179dec (B3hex), the vertical line of the box drawing block. Characters 249dec (F9hex) and 250dec (FAhex) are almost indistinguishable: the first is slightly larger than the second, which resembles the typographic middle dot (·). The character 255 (FFhex) is merely blank, and acts as a kind of non-breaking space in order to arrange math formulae.

Internationalization

CP437 has a series of international characters, mainly values 128dec to 175dec (80hex to AFhex). However, it lacks many characters important to several Western languages:

  • Spanish (Á, Í, Ó, Ú), French (À, Â, È, Ê, Ë, Ì, Î, Ï, Ô, Œ, œ, Ù, Û), and Portuguese (Ã, ã, Õ, õ).
  • German sharp S (ß) shares its code point with the beta symbol (β).
  • Scandinavian lacks Ø and ø. Character number 237dec (EDhex), the empty set symbol, could be used as a surrogate, but its spacing is awkward for display within a word. To compensate, the Norwegian and Danish code pages (CP865 and CP861), replaced cent (¢) with ø, and yen (¥) with Ø.
  • Most Greek alphabet symbols. (They were included in the Greek-language code pages CP737 and CP869.)

Along with the cent (¢), pound sterling (£) and yen/yuan (¥) currency symbols, it has a couple of 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 CP850 (DOS Latin-1), CP852 (DOS Central-European) and CP737 (DOS Greek), filled the gaps for international use with some compatibility with CP437 by retaining the single and double box-drawing characters, while discarding the mixed ones (e.g. horizontal double/vertical single). All CP437 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

References

  1. ^ The Extended ASCII Chart
    Note: CP437 is an extended ASCII code page, but is not the extended ASCII, because numerous incompatible extensions exist.
  2. ^ OEM font Definition
  3. ^ MS LineDraw - Version 2.00
  4. ^ WD97: MS LineDraw Font Not Usable in Word
  5. ^ The Unicode Consortium, The Unicode Standard 4.0, Chapter 7, "European Alphabetic Scripts", p176. PDF version
  6. ^ Richard Wilton, Programmer's Guide to PC & PS/2 Video Systems, 1987, Microsoft Press.

External links


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