This week, I present the first in an occasional series of Windows 2000 Ready columns that I'll devote to defining new Windows 2000 (Win2K) terms and concepts. This series will culminate in a Win2K glossary on the Windows NT Magazine Web site. If you'd like me to address any particular Win2K topics, acronyms, or concepts, email me at zubair@winntmag.com.

Allocation Unit Size
Also known as cluster size, allocation unit size is the smallest amount of hard disk space that Win2K uses to hold a file. Generally, smaller allocation unit sizes result in more efficient use of hard disk space. You can specify the allocation unit size when you format a hard disk drive. If you don't specify a size, Win2K defaults to a size based on the size of the volume. Use format /A: at the command prompt to override the default allocation unit size, where can be 512, 1024, 2048, 4096, 8192, 16K, 32K, and 64K for FAT, FAT32, and NTFS. FAT and FAT32 also support 128K and 256K for sector sizes greater than 512 bytes. You can't use NTFS compression for allocation unit sizes larger than 4096 bytes.

Basic Disk
The Basic disk is a physical disk that can contain primary partitions, extended partitions, or logical drives in extended partitions. A Basic disk is visible to MS-DOS and might contain spanned, striped, mirrored, or RAID5 volumes from previous versions of Windows NT. When you install Win2K, the OS initializes your hard disk as a Basic disk. By right-clicking the Basic disk in Disk Management, you can convert a Basic disk to a Dynamic disk and take advantage of its fault-tolerance features. You can perform certain tasks on a Basic disk only, including formatting a partition and marking it active; creating and deleting primary partitions, extended partitions, and logical drives; and repairing a mirror set or stripe set with parity.

Dynamic Disk
A Dynamic disk is a physical disk you can manage only with Win2K Disk Management. A Dynamic disk, which can only contain dynamic volumes that Disk Management created, isn't visible to MS-DOS. Unlike Basic disks, Dynamic disks can't contain partitions or logical drives. You can perform certain tasks on a Dynamic disk only, including creating a simple, spanned, striped, mirrored, or RAID5 volume; extending a simple or spanned volume; repairing a mirrored or RAID5 volume; and reactivating a missing disk. If you decide to convert a Dynamic disk back to a Basic disk, you'll have to remove all the volumes from the Dynamic disk first.

Global Catalog
A Global Catalog (GC) is a database that contains every object in the Active Directory (AD), but with a limited number of attributes for each object. Win2K automatically creates a GC on the first domain controller in the forest. This GC contains a complete replica of all the AD objects on the host domain and a partial replica of every other domain in the forest. Users (with the exception of domain administrators) can't log on to the network if a GC isn't available. A GC provides universal group information to domain controllers at logon and lets network users locate resources in the AD throughout the forest.

Gratuitous ARP
Gratuitous Address Resolution Protocol (ARP) is a TCP/IP utility that ensures the uniqueness of a client’s IP address. A Win2K DHCP-enabled client can automatically self-configure an IP address when a DHCP server isn't available. But before a client uses the IP address, the client uses a gratuitous ARP to verify that no other client on the network segment is using the same address.

IP/ATM
Internet Protocol/asynchronous transfer mode (IP/ATM) is a group of services that includes three main components: an IP/ATM client, an ATM ARP server, and a Multicast Address Resolution Server (MARS). The IP/ATM client contains the ATM adapter for contacting the MARS server. The ATM ARP server, which contains a database of IP and ATM addresses of all the clients, resolves broadcast and multicast IP addresses to ATM addresses. MARS resolves multicast IP addresses to ATM addresses of those clients that have joined a multicast group. Windows 2000 Server (Win2K Server) includes an ATM ARP/MARS service. To simplify configuration, Microsoft has decided to use the following predetermined address in Win2K by default: 4700790001020000000000000000A03E00000200.

LDAP
Lightweight Directory Access Protocol (LDAP), an Internet Engineering Task Force (IETF) standard, is a communication protocol that Win2K uses on TCP/IP networks to access directory services. The protocol defines how a directory client can access information in a directory server. AD supports LDAP versions 2 and 3. Win2K clients use LDAP to access domain controllers (e.g., to log on to the network) and GC servers (e.g., to locate shared resources on the network).

Round Robin
Round robin is a technique that DNS uses to distribute a load among multiple hosts. When a client sends a query to the DNS server for a host that contains multiple resource records, the server round robins (rotates) the order of IP addresses in the responses. For example, if a client sends a query to a multihomed machine that has A (host) resource records MARS A 169.154.1.1, MARS A 169.154.1.2, and MARS A 169.154.1.3, the DNS server will answer client requests in the following manner: The first client will receive the answer in the order 169.154.1.1, 169.154.1.2, and 169.154.1.3; the second client will receive 169.154.1.2, 169.254.1.3, and 169.254.1.1; the third client will receive 169.154.1.3, 169.254.1.1, and 169.254.1.2; and so on.