An index card (or System card in Australian English) is heavy paper stock cut to a standard size. Index cards are often used for recording individual items of information that can then be easily rearranged and filed. It was invented by Carl Linnaeus. The most common size in the United States and Russia is 3 by 5 inches (76 by 127 mm), hence the common name 3-by-5 card. Other sizes widely available include 4 by 6 inches (102 by 152 mm), 5 by 8 inches (127 by 203 mm) and ISO-size A7 (74 mm by 105 mm). Cards are available in blank, ruled and grid styles in a variety of colors. Special divider cards with protruding tabs and a variety of cases and trays to hold the cards are also sold by stationers.
As the name implies, index cards were widely used in the nineteenth and twentieth centuries to create an index to large collections of documents. A major law firm, for example, might have a room full of metal cabinets with drawers designed to hold index cards. Clerks might fill out several cards for an individual document or legal case, allowing them to be filed alphabetically under a number of terms.
One innovation based on the index card was the edge-notched card, which was an index card with prepunched holes near the edges. Users of this system assigned a category to each hole position, and then notched out the hole when a card fit a category. To locate all cards that matched a category, a long, thin rod or "needle" was inserted through the corresponding holes in a tray of cards, the cards were lifted out of the tray, and all of the cards with notched holes dropped out of the stack. The system could also be used to locate all the cards that belonged to one or more categories at once by using more than one needle.
While computers have largely supplanted index cards and especially edge-notched cards, index cards are still a popular way of organizing ideas, quotes, vocabulary words, and references while researching and writing books, articles, and essays, and for managing any kind of free-form information. These cards are also very useful in school, where students might record information. Index cards can be hole-punched and be stored on a ring, or be placed inside a small box.
The 4 by 6 inch (102 by 152 mm) and A6 (105 by 148 mm) sizes are the only standard sizes that qualify for "postcard rate" when mailed through the United States Postal Service.
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An index card (or System card in Australian English) consists of heavy paper stock cut to a standard size, used for recording and storing small amounts of discrete data. It was invented by Carl Linnaeus.
The most common size for index cards in North America and Russia is 3 by 5 inches (76.2 by 127.0 mm), hence the common name 3-by-5 card. Other sizes widely available include 4 by 6 inches (101.6 by 152.4 mm), 5 by 8 inches (127.0 by 203.2 mm) and ISO-size A7 (74 by 105 mm/2.9 by 4.1 in). Cards are available in blank, ruled and grid styles in a variety of colors. Special divider cards with protruding tabs and a variety of cases and trays to hold the cards are also sold by stationers and office product companies.
Index cards are used for a wide range of applications and environments: in the home to record and store recipes, shopping lists, contact information and other organizational data; in business to record presentation notes, project research and notes and contact information; in schools as flash cards or other visual aids; and in academic research to hold data such as bibliographical citations or notes. An often-suggested organization method is to use the smaller 3-inch by 5-inch cards to record the title and citation information of works cited, while using larger cards for recording quotes or other data.
Until the conversion of library catalogs beginning in the 1980s, the primary tool used to locate books was the card catalog in which every book was filed with three cards, filed alphabetically under its title, author and subject (if non-fiction.) Similar catalogs were used by law firms and other organizations to organize large quantities of stored documents. However, the adoption of standard cataloging protocols throughout nations with international agreements, along with the rise of the Internet and the conversion of cataloging systems to digital storage and retrieval, have made widespread use of index cards for cataloging purposes obsolete.