Credit is a method of selling goods or services without the buyer having cash in hand. A credit card is only an automatic way of offering credit to a consumer.
Today, every credit card carries an identifying number that speeds shopping transactions. Imagine what a credit purchase would be like without it, the sales person would have to record your identity, billing address, and terms of repayment.
The first use of magnetic stripes on cards was in the early 1960's, when the London Transit Authority installed a magnetic stripe system. San Francisco Bay Area Rapid Transit installed a paper based ticket the same size as the credit cards in the late 1960's.