Serial and parallel ports, mouse and keyboard connectors, expansion slots and multiple drive bays. Instead, there are typically several Universal Serial Bus ports, plus network and monitor connections. And they've all been designed for Windows 2000, though some are available with Windows 98 or Windows Me. These machines can be smaller, in part, because they have been designed using some components that were originally designed for laptops. But because they don't have the severe space and weight restrictions of portables, they can afford to use larger, heavier, previous-generation components that are relatively cheap.
Price is another driving force for eliminating the older peripheral connections.
It's important to say that these are business machines, not home computers. They're designed for easy management and maintenance. All make it easy to replace memory or hard drive quickly and without tools. All are designed to be connected to a network and managed by a server, though they aren't thin clients in the traditional sense. An Overall View These are remarkably good machines for the money.