Portable computers are available with a wide variety of feature sets. Larger models, often called notebooks or laptops, generally have a full-size display screen, a keyboard with full-size alpha-numeric keys, a mass storage medium such as a hard drive, removable storage media such as a CD-ROM drive and a floppy drive, and standard parallel and serial ports. Smaller models, sometimes called sub-notebooks, are generally more portable, but at the expense of some of their features. For example, one or more of the storage media can be omitted, the screen and keyboard can be made more compact, and ports can be omitted or simplified. The smallest machines, often called palm-tops or personal digital assistants (PDAs), fit in ordinary jacket pockets, but typically have quite limited displays, keyboards, storage, and ports.
Each of these types of machines provides a different trade-off between portability and features, and is therefore best suited to certain tasks. While smaller machines are easier to carry, they can be tedious to use to type long documents, and their processing and storage capabilities may be insufficient for some applications. Conversely, larger machines are more comfortable to use and exhibit more powerful capabilities, but their size and weight makes them cumbersome to transport.