Editing Punched card (section)

=== IBM 80-column format and character codes ===
[[File:FortranCardPROJ039.agr.jpg|thumb|Punched card from a [[Fortran]] program: Z(1) = Y + W(1), plus sorting information in the last 8 columns.]]

By the late 1920s, customers wanted to store more data on each punched card. [[Thomas J. Watson|Thomas J. Watson Sr.]], IBM's head, asked two of his top inventors, [[Clair D. Lake]] and [[J. Royden Pierce]], to independently develop ways to increase data capacity without increasing the size of the punched card. Pierce wanted to keep round holes and 45 columns but to allow each column to store more data; Lake suggested rectangular holes, which could be spaced more tightly, allowing 80 columns per punched card, thereby nearly doubling the capacity of the older format.<ref name="Lake_1928"/> Watson picked the latter solution, introduced as ''The IBM Card'', in part because it was compatible with existing tabulator designs and in part because it could be protected by patents and give the company a distinctive advantage.<ref name="IBM_2012"/>

This IBM card format, introduced in 1928,<ref name="IBM_1928"/> has rectangular holes, 80 columns, and 10 rows.<ref name="Pugh_IBM"/> Card size is {{convert|7+3/8|by|3+1/4|in|mm}}. The cards are made of smooth stock, {{convert|0.007|in|um}} thick. There are about 143 cards to the inch ({{#expr:143/2.54round0}}/cm). In 1964, IBM changed from square to round corners.<ref name="IBM_OldNew"/> They come typically in boxes of 2,000 cards<ref name="Boyd_2007"/> or as [[Continuous stationery|continuous form]] cards. Continuous form cards could be both pre-numbered and pre-punched for document control (checks, for example).<ref name="IBM_1953"/>

Initially designed to record responses to [[yes–no question]]s, support for numeric, [[Character encoding|alphabetic and special characters]] was added through the use of columns and zones. The top three positions of a column are called '''zone punching positions''', 12 (top), 11, and 0 (0 may be either a zone punch or a digit punch).<ref name="ReferenceA_1961"/> For decimal data the lower ten positions are called '''digit punching positions''', 0 (top) through 9.<ref name="ReferenceA_1961"/> An arithmetic sign can be specified for a decimal field by '''overpunching''' the field's rightmost column with a zone punch: 12 for plus, 11 for minus (CR). For [[Pound sterling]] [[Coins of the pound sterling#Pre-decimal coinage|pre-decimalization currency]] a [[penny]] column represents the values zero through eleven; 10 (top), 11, then 0 through 9 as above. An arithmetic sign can be punched in the adjacent [[shilling]] column.<ref name="Cemach_1951"/>{{rp|page=9}} Zone punches had other uses in processing, such as indicating a master card.<ref name="IBM_1959_2"/>

[[File:Blue-punch-card-front-horiz.png|thumb|An 80-column punched card with the extended character set introduced with [[EBCDIC]] in 1964.]]

Diagram:<ref name="Iowa_2"/>

<pre style="width:fit-content;white-spacing:nowrap">
    _______________________________________________
   / &-0123456789ABCDEFGHIJKLMNOPQR/STUVWXYZ
12|  x           xxxxxxxxx
11|   x                   xxxxxxxxx
 0|    x                           xxxxxxxxx
 1|     x        x        x        x
 2|      x        x        x        x
 3|       x        x        x        x
 4|        x        x        x        x
 5|         x        x        x        x
 6|          x        x        x        x
 7|           x        x        x        x
 8|            x        x        x        x
 9|             x        x        x        x
  |________________________________________________
</pre>
''Note: The 11 and 12 zones were also called the X and Y zones, respectively.''

In 1931, IBM began introducing upper-case letters and special characters (Powers-Samas had developed the first commercial alphabetic punched card representation in 1921).<ref name="Rojas_2001"/><ref name="Pugh_1995"/><ref group="nb" name="NB_Special_characters"/> The 26 letters have two punches (zone [12,11,0] + digit [1–9]). The languages of Germany, Sweden, Denmark, Norway, Spain, Portugal and Finland require up to three additional letters; their punching is not shown here.<ref name="Mackenzie_1980"/>{{rp|pages=88–90}} Most special characters have two or three punches (zone [12,11,0, or none] + digit [2–7] + 8); a few special characters were exceptions: "&" is 12 only, "-" is 11 only, and "/" is 0 + 1). The Space character has no punches.<ref name="Mackenzie_1980"/>{{rp|page=38}} The information represented in a column by a combination of zones [12, 11, 0] and digits [0–9] is dependent on the use of that column. For example, the combination "12-1" is the letter "A" in an alphabetic column, a plus signed digit "1" in a signed numeric column, or an unsigned digit "1" in a column where the "12" has some other use. The introduction of [[EBCDIC]] in 1964 defined columns with as many as six punches (zones [12,11,0,8,9] + digit [1–7]). IBM and other manufacturers used many different 80-column card [[character encoding]]s.<ref name="Winter_80"/><ref name="Jones_2"/> A 1969 American National Standard defined the punches for 128 characters and was named the ''Hollerith Punched Card Code'' (often referred to simply as ''Hollerith Card Code''), honoring Hollerith.<ref name="Mackenzie_1980"/>{{rp|page=7}}

[[File:IBM1130CopyCard.agr.jpg|thumb|[[Binary code|Binary]] punched card.]]

For some computer applications, [[Binary numeral system|binary]] formats were used, where each hole represented a single binary digit (or "[[bit]]"), every column (or row) is treated as a simple [[bit field]], and every combination of holes is permitted.

For example, on the [[IBM 701]]<ref name="IBM_1953_Principles"/> and [[IBM 704]],<ref name="IBM_1955_EDP"/> card data was read, using an [[IBM 711]], into memory in row binary format. For each of the twelve rows of the card, 72 of the 80 columns, skipping the other eight, would be read into two [[36-bit]] words, requiring 864 bits to store the whole card; a control panel was used to select the 72 columns to be read. Software would translate this data into the desired form. One convention was to use columns 1 through 72 for data, and columns 73 through 80 to sequentially number the cards, as shown in the picture above of a punched card for FORTRAN. Such numbered cards could be sorted by machine so that if a deck was dropped the sorting machine could be used to arrange it back in order. This convention continued to be used in FORTRAN, even in later systems where the data in all 80 columns could be read.

The IBM card readers 3504, [[IBM 3505|3505]] and the multifunction unit 3525 used a different encoding scheme for column binary data, also known as [[card image]], where each column, split into two rows of 6 (12–3 and 4–9) was encoded into two 8-bit bytes, holes in each group represented by bits 2 to 7 (MSb [[Bit numbering|numbering]], bit 0 and 1 unused ) in successive bytes. This required 160 8-bit bytes, or 1280 bits, to store the whole card.<ref name="IBM GA21-9124-5" />

As an aid to humans who had to deal with the punched cards, the IBM 026 and later 029 and 129 key punch machines could print human-readable text above each of the 80 columns.

[[File:IBM lace card.jpg|thumb|left|Invalid "lace cards" such as this pose mechanical problems for card readers.]]

As a prank, punched cards could be made where every possible punch position had a hole. Such "[[lace card]]s" lacked structural strength, and would frequently buckle and jam inside the machine.<ref name="Raymond_1991"/>

The IBM 80-column punched card format dominated the industry, becoming known as just '''IBM cards''', even though other companies made cards and equipment to process them.<ref name="Maxfield_2011"/>

[[File:Punch-card-5081.jpg|thumb|A 5081 card from a non-IBM manufacturer.]]

One of the most common punched card formats is the IBM 5081 card format, a general purpose layout with no field divisions. This format has digits printed on it corresponding to the punch positions of the digits in each of the 80 columns. Other punched card vendors manufactured cards with this same layout and number.