be linked together to form forests. Active Directory services could always be installed on a Windows 2000 Server Standard, Advanced, or Datacenter computer, and cannot be installed on a Windows 2000 Professional computer. However, Windows 2000 Professional is the first client operating system able to exploit Active Directory's new features. As part of an organization's migration, Windows NT clients continued to function until all clients were upgraded to Windows 2000 Professional, at which point the Active Directory domain could be switched to native mode and maximum functionality achieved. Active Directory requires a DNS server that supports SRV resource records, or that an organization's existing DNS infrastructure be upgraded to support this. There should be one or more domain controllers to hold the Active Directory database and provide Active Directory directory services. Volume fault tolerance Along with support for simple, spanned and striped volumes, the Windows 2000 Server family also supports fault-tolerant volume types. The types supported are mirrored volumes and RAID-5 volumes: Mirrored volumes: the volume contains several disks, and when data is written to one it is also written to the other disks. This means that if one disk fails, the data can be totally recovered from the other disk. Mirrored volumes are also known as RAID-1. RAID-5 volumes: a RAID-5 volume consists of multiple disks, and it uses block-level striping with parity data distributed across all member disks. Should a disk fail in the array, the parity blocks from the surviving disks are combined mathematically with the data blocks from the surviving disks to reconstruct the data on the failed drive "on-the-fly." Deployment Windows 2000 can be deployed to a site via various methods. It can be installed onto servers via traditional media (such as CD) or via distribution folders that reside on a shared folder. Installations can be attended or unattended. During a manual installation, the administrator must specify configuration options. Unattended installations are scripted via an answer file, or a predefined script in the form of an INI file that has all the options filled in. An answer file can be created manually or using the graphical Setup manager. The Winnt.exe or Winnt32.exe program then uses that answer file to automate the installation. Unattended installations can be performed via a bootable CD, using Microsoft Systems Management Server (SMS), via the System Preparation Tool (Sysprep), via the Winnt32.exe program using the /syspart switch or via Remote Installation