Code page 437: Wikis

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Code page 437, as rendered by the IBM PC using an EGA.

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 more strict sense, this character set was not born as a real code page (in its present sense) but being merely the graphical glyph repertoire available in the ROM of the IBM Enhanced Graphics Adapter (EGA). This bitmapped font is a 8 by 16 pixels-per-character version of the 8 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. Today, it 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 a 8 bit character code point (see details), giving 256 possible values for graphic characters. This way, beyond the original ASCII graphical character set (values 32 to 126, 95 in total), the implementors put in ROM a handful of miscellaneous characters even for the range 0 to 31, reserved in ASCII for control (non graphical) purposes.

So this code page has two main uses: as an information interchange code (through files and telecom), in which the values 0 to 127 plays the same role as in ASCII plus the international text characters 128 to 175 (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.

Characters

The following is a table representing CP437 using the equivalent Unicode characters. Standard ASCII and ISO 8859-1 (Latin-1) character glyphs, along with the Greek letters, are shown as coloured cells.

Due to the dual use of values in the range 0 to 31 (hexadecimal 00 to 1F), there are two sets for these, the first being their meanings as ASCII control characters and the second their graphical output on screen/printer.

For value 127 (7F), its graphical output is shown in the last table, its meaning being the ASCII control character "DEL" (delete), Unicode value U+007F. A font in Microsoft Windows called Terminal replicates most but not all of these characters.

—0 —1 —2 —3 —4 —5 —6 —7 —8 —9 —A —B —C —D —E —F

0−

NUL
0000
0
SOH
0001
1
STX
0002
2
ETX
0003
3
EOT
0004
4
ENQ
0005
5
ACK
0006
6
BEL
0007
7
BS
0008
8
HT
0009
9
LF
000A
10
VT
000B
11
FF
000C
12
CR
000D
13
SO
000E
14
SI
000F
15

1−

DLE
0010
16
DC1
0011
17
DC2
0012
18
DC3
0013
19
DC4
0014
20
NAK
0015
21
SYN
0016
22
ETB
0017
23
CAN
0018
24
EM
0019
25
SUB
001A
26
ESC
001B
27
FS
001C
28
GS
001D
29
RS
001E
30
US
001F
31
—0 —1 —2 —3 —4 —5 —6 —7 —8 —9 —A —B —C —D —E —F
CP437
—0 —1 —2 —3 —4 —5 —6 —7 —8 —9 —A —B —C —D —E —F

0−

FSP
2007
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

Legend: yellow cells are control characters, blue cells are punctuation, purple cells are numbers, green cells are ASCII letters, and tan cells are international letters.

NOTE: graphical output for characters 0 (00), 32 (20), and 255 (FF) are mere blank cells, without printable marks of any kind.

NOTE: the graphical output chosen for character number 0 (00) is U+2007 FIGURE SPACE (FSP), a space of the same width as digits in the variable-pitch fonts.

Below is an example of Terminal (based on code page 437) typing. If you don't have this font, the text below will be displayed by monospace typeface.

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

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`.

In programs that only support Windows-1252, attempts to enter characters from CP437 will result in an attempt at transliteration for the Greek letters (αΓπΣστΦΘΩδφε become aGpSstFTOdfe) and graphical approximations for other characters (∩ and ⁿ both become n, √ becomes v, etc.).

Difference from ASCII

CP437 is based on ASCII, with the following modifications:

• Codes from the C0 control range (hex 00 to 1F) and ASCII DEL (7F) can assume their original function as controls, but when placed to display text buffer in text mode and then viewed, they show as graphics; see above. For example, DEL and some of C0 control codes have a graphic appearance in a screen editor like MS-DOS Editor and when put to the screen via type command or so. The graphics are various, such as smiling faces, card suits and musical notes. Code 127 (7F), DEL, similarly shows as a graphic (a house). Though, this is is not specific to CP437 itself, but to all DOS (or so named Windows OEM, which is nearly the same) code pages, which usually resemble CP437.
• The high-bit range, 128 to 255 (80 to FF), is mapped to various symbols: a few European characters (accented Latin vowels, 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 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 graphic character set selection, often accused of being somewhat bizarre, has some internal logic:

• Table rows 0 and 1, codes 0 to 31 (00 to 1F), are assorted dingbats (complementary and decorative characters). The isolated character 127 (7F) also belongs to this group.
• Table rows 2 to 7 (except character 127, 7F), codes 32 to 126 (20 to 7E), are the standard ASCII printable characters.
• Table rows 8 to 10 (8 to A), codes 128 to 175 (80 to AF), are a picked selection of international text characters.
• Table rows 11 to 13 (B to D), codes 176 to 223 (B0 to DF), are box drawing and block characters. This block is subarranged in such way that characters 192 to 223 (C0 to DF) of the rows 12 and 13 (C and D) have all right arms (except 217, D9) or right filled areas (except 221, DD), and this is due to the following technical reason[3]: the original IBM PC MDA display adapter had stored the CP437 character glyphs as little bitmaps eight pixels wide, but displays them every nine pixels on screen, eight plus an additional gap, for visual enhancement. Thus, characters with connection designs at their right side must duplicate their eighth pixels in order to not interrupt visually the lines/filled surfaces they built when are put consecutively. This pixel extension is done by special hardware circuitry, and only this character subset is affected.
• Table rows 14 and 15 (E and F), codes 224 to 255 (E0 to FF) are devoted to mathematical symbols, where the first twelve are a picked selection of Greek letters commonly used in physics. Characters 244 (F4) and 245 (F5) are the upper and lower portion of an italic long S, the symbol used as integral sign (), and they can be extended through the character 179 (B3), the vertical line of the box drawing block. Characters 249 (F9) and 250 (FA) are almost indistinguishable: the first is slightly larger than the second, which resembles the typographic middle dot (·). The character 255 (FF) 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 128 to 175 (hex 80 to AF). However, it lacks many characters important to several Western languages:

• It lacks many characters for 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).
• It has umlauts for German (Ä, ä, Ö, ö, Ü, ü), but sharp S (ß) must be represented with the beta symbol (β).
• It has Scandinavian Æ, æ, Å, å, Ä, ä but lacks Ø and ø (character number 237, empty set, may be used as a surrogate, but is not properly displayed within a word). To compensate the Norwegian and Danish edition replaced cent (¢) with ø, and yen (¥) with Ø.

Along with the cent (¢), pound sterling (£) and yen/yuan (¥) currency symbols, it has a couple of European currency symbols, for the florin (ƒ, Netherlands) and the peseta (₧, Spain). The presence of the last is a surprise, 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". The only related fact is that Spanish models of the IBM electric typewriter also had a single type 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 are in Unicode and in Microsoft's WGL4 character set, therefore in most of the fonts on Microsoft Windows, and also in the default VGA font of the Linux kernel, and the ISO 10646 fonts for X11.

Multiple-meaning character glyphs

Along with the characters in the range 0 to 31 (hex 00 to 1F), which can be interpreted as ASCII controls as well as graphical dingbats, some characters with ambiguous look (to the eyes of its implementors, not to the eyes of a typographer) have overloaded meanings, depending upon context:

• 225 (E1) is both the German sharp S (U+00DF, ß) and the Greek lowercase beta (U+03B2, β).
• 227 (E3) 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 as such, can be used for the Greek capital pi (U+03A0, Π) or the n-ary product sign (U+220F, ∏).
• 228 (E4) is both the n-ary summation sign (U+2211, ∑) and the Greek uppercase sigma (U+03A3, Σ).
• 230 (E6) is both the micro sign (U+00B5, µ) and the Greek lowercase mu (U+03BC, μ).
• 234 (EA) is both the ohm sign (U+2126, Ω) and the Greek uppercase omega (U+03A9, Ω) (note that in Unicode as well, the ohm sign is canonically equivalent to the capital omega, and its use is discouraged in favor of capital omega [1]).
• 235 (EB) is the Greek lowercase delta (U+03B4, δ), but it has been used also as an approximated surrogate for the Icelandic lowercase eth (U+00F0, ð) and the partial derivative sign (U+2202, ∂).
• 237 (ED) is supposed to used as Greek lowercase phi, but is mainly used as the empty set sign (U+2205, $\varnothing$) and it was also used as Greek phi symbol in italics (U+03D5, $\phi\,\!$) to name angles, diameter sign (U+2300, $\varnothing$) and as an approximated surrogate for the Latin lowercase O with stroke (U+00F8, ø). The reason why it is used rarely as Greek lowercase phi is because its IBM original shape, which seems to be merely a circle crossed by a slash, does not closely resemble this Greek lowercase letter.
• 238 (EE) is both the Greek lowercase epsilon (U+03B5, ε) and the element-of sign (U+2208, ∈). Also, in some dot matrix ticket printers (with CP437 in ROM), it is used today in place of the euro sign (U+20AC, €), in the European countries where the euro is the official currency.
 Fixed control values− Alternate character values− NUL 0000 0 DEL 007F 127 β 03B2 225 $\phi\,\!$ 2205 237 ∈ 2208 238

It should be noted that the Unicode character U+03D5 GREEK PHI SYMBOL ($\phi\,\!$) would be a better choice[4] for value number 237 (ED) of CP437.

The main reason for these ambiguities is that the CP437 character set of the original IBM PC MDA and CGA display adapters, as well as that of compatible printers, was fixed in ROM and could not be changed by software, so developers and users tried to take the maximum advantage of the available resources.

Implementors of mapping tables to Unicode should note that these "unified" characters may not have a unique, single meaning: the correct choice depends upon context.

References

1. ^ The Extended ASCII Chart
2. ^ OEM font Definition
3. ^ Richard Wilton, Programmer's Guide to PC & PS/2 Video Systems, 1987, Microsoft Press.
4. ^ UTR #25: Unicode and Mathematics — Representative Glyphs for Greek Phi