Microsoft Knowledge Base Article 909520 contains the following summary and introduction:
SUMMARYMicrosoft has released an update for Microsoft Base Smart Card Cryptographic Service Provider (CSP). The "Article contents" section describes the information that this article contains about this update.
INTRODUCTIONThis article describes the software update for Base Smart Card CSP. This update lets smart card vendors more easily enable their smart cards on Microsoft Windows by using a lightweight proprietary card module instead of a full proprietary CSP.
This update lets users use smart cards from vendors who use card modules instead of a full CSP.
Note To enable most smart card security, the user must still enroll for certificates from a trusted public key infrastructure.