Access Control List: A list of permissions attached to an object, which specifies who or what is allowed to access the object and what operations are allowed to be performed on the object.

Active Directory: An implementation of LDAP directory services by Microsoft for use primarily in Windows environments.

Advanced Encryption Standard: A block cipher adopted as an encryption standard by the U.S. government, also known as Rijndael.

Advanced Host Controller Interface: A hardware mechanism that allows software to communicate with Serial ATA devices such as host bus adapters which are designed to offer features not offered by Parallel ATA controllers besides higher speeds, such as hot-plugging and native command queuing.

Application Information Service: A service in Windows Vista. See Vista’s Application Information Service

Application Layer Gateway: A service in Windows Vista. See Vista’s Application Layer Gateway Service

Access Point: A device that connects wireless communication devices together to form a wireless network.

Audio Stream Input/Output: A computer soundcard driver protocol for digital audio specified by Steinberg, providing a low-latency and high fidelity interface between a software application and a computer’s sound card. Whereas Microsoft’s DirectSound is commonly used as a stereo input and output for non-professional users, ASIO allows musicians and sound engineers to process their audio via Windows’ computer software instead of external hardware.

Active State Power Management: Allows power to be incrementally reduced to individual serial links in a PCI Express fabric as a link becomes less active.

Active Template Library: A set of template-based C++ classes by Microsoft that simplify the programming of Component Object Model (COM) objects.

Asynchronous Transfer Mode: A cell relay, Circuit switching network and data link layer protocol which encodes data traffic into small fixed-sized cells.

Authenticated Internet Protocol: A Microsoft proprietary extension of the IKE cryptographic protocol which adds a second authentication to the standard IKE authentication which increases security and deployability of IPsec VPNs.