and that the client OS is not aware that it is not running off a hard disk. This is why this approach is sometimes named "Virtual Hard Disk" or "Network Virtual Disk". This third approach makes it easier to use client OS than having a complete disk image in RAM or using a read-only file system. In this approach, the system uses some "write cache" that stores every data that a diskless node has written. This write cache is usually a file, stored on a server (or on the client storage if any). It can also be a portion of the client RAM. This write cache can be persistent or volatile. When volatile, all the data that has been written by a specific client to the virtual disk are dismissed when said client is rebooted, and yet, user data can remain persistent if recorded in user (roaming) profiles or home folders (that are stored on remote servers). The two major commercial products (the one from Hewlett-Packard, and the other one from Citrix Systems) that allow the deployment of Diskless Nodes that can boot Microsoft Windows or Linux client OS use such write caches. The Citrix product cannot use persistent write cache, but VHD and HP product can. Diskless Windows nodes Windows 3.x and Windows 95 OSR1 supported Remote Boot operations, from NetWare servers, Windows NT Servers and even DEC Pathworks servers. Third party software vendors such as Qualystem (acquired by Neoware), LanWorks (acquired by 3Com), Ardence (acquired by Citrix), APCT and Xtreamining Technology have developed and marketed software products aimed to remote-boot newer versions of the Windows product line: Windows 95 OSR2 and Windows 98 were supported by Qualystem and Lanworks, Windows NT was supported by APCT and Ardence (called VenturCom at that time), and Windows 2000/XP/2003/Vista/Windows 7 are supported by Hewlett Packard (which acquired Neoware which had previously acquired Qualystem) and Citrix Systems (which acquired Ardence). Comparison with fat clients Software installation and maintenance With essentially a single OS image for an array of machines (with perhaps some customizations for differences in hardware configurations among the nodes), installing software and maintaining installed software can be more efficient. Furthermore, any system changes made during operation (due to user action, worms, viruses, etc.) can be either wiped out when the power is removed (if the image is copied to a local RAM disk) such as Windows XP Embedded remote boot or