In recent years, device makers have been exploring this question with mixed results.
Lenovo sold a notebook less than a year ago with a slide-out second screen, but no longer offers such a model. Other computer makers -- including ASUS, MSI and even the One Laptop per Child organization -- have presented concepts for dual-screen notebooks and tablets, but have not released actual products. The biggest success so far with the dual-screen concept has been in the area of gaming, with the Nintendo DS.
Still, there are several devices utilizing two screens that you can buy now - plus a couple more that their makers hope to bring to market soon. Here's a rundown.