as the hardcopy line-mode 3215, the graphical 3270 family, and the integrated console on newer System/390 and System Z machines. Other users can then access running virtual machines using the DIAL command at the logon screen, which will connect their terminal to the first available emulated 3270 device, or the first available 2703 device if the user is DIALing from a typewriter terminal. Another copy of VM. A second level instance of VM can be fully virtualized inside a virtual machine. This is how VM development and testing is done (a second-level VM can potentially implement a different virtualization of the hardware). This technique was used to develop S/370 software before S/370 hardware was available, and it has continued to play a role in new hardware development at IBM. The literature cites practical examples of virtualization five levels deep. Levels of VM below the top are also treated as applications but with exceptional privileges. A copy of the mainframe version of AIX or Linux. In the mainframe environment, these operating systems often run under VM, and are handled like other guest operating systems. (They can also run as 'native' operating systems on the bare hardware.) There was also the short-lived IX/370, as well as S/370 and S/390 versions of AIX (AIX/370 and AIX/ESA). A specialized VM subsystem. Several non-CMS systems run within VM-CP virtual machines, providing services to CMS users such as spooling, interprocess communications, specialized device support, and networking. They operate behind the scenes, extending the services available to CMS without adding to the VM-CP control program. By running in separate virtual machines, they receive the same security and reliability protections as other VM users. Examples include: RSCS (Remote Spooling and Communication Subsystem, aka VNET) – communication and information transfer facilities between virtual machines and other systems RACF (Resource Access Control Facility) — a security system Shared File System (SFS), which organizes shared files in a directory tree (the servers are commonly named "VMSERVx" VTAM (Virtual Telecommunications Access Method) – a facility that provides support for a Systems Network Architecture network PVM (VM/Pass-Through Facility) – a facility that provides remote access to other VM systems TCPIP, SMTP, FTPSERVE, PORTMAP, VMNFS – a set of service machines that provide TCP/IP networking to VM/CMS Db2 Server for VM – a SQL database system, the servers are often named similarly to "SQLMACH" and "SQLMSTR" DIRMAINT – A simplified user directory management system