Index cards are ubiquitous, but how much do you really know about them? Their long history as a system for cataloguing data has been swept aside, as databases have long since taken over that function. However, index cards continue to flourish as an inexpensive, convenient way to jot things down.
Using cards to create an index was the brainchild of 18th century naturalist Carl Linnaeus, who is known as "the father of modern taxonomy" for his work on categorizing species. He needed a system for organizing data that was expandable and able to be rearranged easily. So he kept each datum on individual sheets and could add new sheets and reorganize simply. Card catalogs as we know them arose in the 19th century, and Melvil Dewey standardized the index cards used in library card catalogs in the 1870s. In the late 1890s, edge-notched cards were invented, which allowed for easy sorting of data by means of a needle-like tool. These edge-notched cards were phased out in the 1980s in favor of computer databases, and they bare no longer sold.
Index cards come in several types, including ruled, blank and grid-patterned. Although usually white, they come in multiple colors, including pink, yellow, blue and green. You also can get cards with color-coded strips at the top. Index cards are sold in shrink-wrapped packages, spiral-bound or perforated. Special tabbed card dividers are available with blank, alphabet, number and monthly tabs. Rolodex business card files use distinctive index cards with two notches in the bottom that slip onto rings that hold them in place.
Standard index cards come in 3 by 5 inches, 4 by 6 inches and 5 by 8 inches. Cards for Rolodex business card files are 2 1/4 by 4 inches. The 3 by 5 inch card was the size used in library card catalogs, and it's still the most common.
The original function of index cards was, in fact, to form indices. Information was written on the cards, and then filed alphabetically or numerically in chests with drawers sized to fit the cards. Today, index cards are often used to make flash cards or for writing notes, outlines and speeches.
Index cards are easily found at office supply stores, supermarkets, drug stores, and discount stores. As of September 2009, a package of 300 3 by 5 inch white ruled index cards cost about $2, and a package of 100 5 by 8 inch mixed color ruled cards cost about $3.