Eventually, with the introduction of the PS/2 line of PCs in 1987, IBM changed the AT's large keyboard plug to the miniplug that's in common use today. (See this page http://www.bbdsoft.com/ keyboard.html for examples.) Mice followed thereafter, although it would be almost 10 years before most systems shipped with only the PS/2-style mouse and keyboard sockets.

But even that wasn't a true move to legacy-free design, because all it really did was change the size and shape of the connectors. And meanwhile, serial/communications, printer, and game ports hadn't changed much at all.

Then USB entered the scene--and the universal serial bus http://www.usb.org/ was a true break from classic PC AT design. Fast, flexible, and extensible, USB could--in theory--handle almost any kind of serial input, including mice, keyboards, printers, modems or other communications, and game device input.

But the move to USB has been hampered by several factors. USB devices may work poorly or not at all on older PCs, and, more importantly, the huge installed base of non-USB peripherals has made the change slow going.

For example, Phil Osako, Gateway's director of product management, says one reason for the slow change is "the large number of customers with legacy ergonomic keyboards, optical mice, and trackballs" who won't want to switch to USB input devices until their older devices are no longer serviceable. There are similar issues with printers, scanners, and other peripherals.

Hewlett-Packard's Brian Schmitz agrees: "Customers understand the benefits of legacy-free, but many are anxious about needing backward compatibility. HP addresses this by providing optional serial/parallel/PS/2 connectivity for those users needing it. This need is diminishing over time."

But it's diminishing only slowly. Osako thinks it will be at least "a couple more years" before we see the last of the legacy ports. By way of example, he points specifically to PDAs and GPS devices "Langa Letter: A Real-Life GPS Road Test," many of which are still coming to market with standard legacy serial ports for connecting to or syncing with PCs. Although third-party adaptors can let these devices connect to USB systems and vice versa (see "USB-To-Anything"), USB won't be able to completely replace legacy ports until peripheral vendors stop shipping legacy-based devices.

Slots, System Buses, And PnP
A PC's slots--the electrical connectors (and the buses they are part of) that are used to plug in add-on circuit boards or cards--are one of the areas that's changed the most since the original PC.