Plug-and-Play is a feature in Windows that enables the automatic self-configuring of devices.
When you plug a device into your PC and Windows knows the identity of the device and tries to retrieve the driver for the device, that is Plug-and-Play.
One of the smaller features in Windows that will likely never see any press is the support of Plug-and-Play with Smart cards.
Historically Smart cards have been tightly integrated with each application using libraries like PKCS #11 or Cryptographic Service Providers.
There are many problems with this approach, for one they seldom lead to true application interoperability, that is without a ton of scenario and application specific work on behalf of each and every application.
The main reason behind the need for the application specific work is the interface contracts for libraries like this are designed for generic cryptographic extensibility and not the narrow capabilities of a smart card.
In simple terms, a smart card can do a handful of things but one of these libraries must do dozens if not hundred of things.
In the Windows XP SP2 timeframe Microsoft introduced a new provider model for Smart Cards was, its was called a Smart Card Mini driver; support for this concept was made available for Windows 2000 and up platforms via a downloadable package.
In this model smart cards vendors only need to expose the minimal set of things the card can actually do in their middleware, the rest of the work necessary to work well in applications is handled by a higher-layer.
In the Windows VISTA time-frame a certification test-suite was also provided, with this suite vendors could test their cards to get an idea if they would work in common Windows scenarios and ensure they meet a basic quality bar.
As a result of completing that test suite successfully vendors can include the "Designed for.." logo's on their marketing materials and distribute the drivers via Windows Update.
Windows 7 builds on this by being able to automatically detect which drivers are appropriate for a given smart card and install them (with no user interaction!).
For users most users this means when they insert their smart cards they "just work", if they pay close attention when they insert a smart card during a interactive session they will see a bubble:
If they click on that bubble they will see the "Driver Software Installation" dialog, beginning searching for device drivers:
This dialog will change to show the driver was installed:
From that point on when the card is inserted the right driver will be automatically loaded for the device, when the user goes into Device Manager they will see a new Smart Cards node:
Another side affect of this is that Smart cards now can take advantage of the improved driver installation facilities in Windows 7, this means that Smart card drivers can be installed before there is a interactive session and by standard (non-administrative) users.
This feature is important for a number of reasons, one of which is that the number one complaint for Smart card deployments is the need to deploy complex proprietary middleware to use them.
A variation on that middleware deployment problem is relation to National ID cards, its one thing for a enterprise to need to deploy middleware for a smart card its another entirely for a government who wants to use smart cards for citizen to government commerce, now for Windows 7 they have a solution to that problem.