It was possible for a TV channel to encode a small amount of data in the vertical blanking period between video frames - this is how subtitles were transmitted, for example. Teletext exploited this feature by encoding entire pages of text into that interval, each with a three digit page number. When the user requested a particular page number through the remote control, the TV set would wait a few seconds until the corresponding page was transmitted, then render it. More expensive TVs would have enough RAM to cache the pages ahead of time, so page access would be instant.