NMI line to permit a "warm start" if the system had locked up. Typically, this would restore the control registers to known good values stored in ROM, without destroying whatever data that the user might currently have loaded. On the Commodore 8-bit machines, the key was hooked up directly or indirectly to the NMI line on the 6502-series CPU, but the reset would take place only if the NMI handler routine in ROM detected that was also being held down when was struck (this combination being the Commodore version of a three finger salute). Commodore also connected the MOS Technology 6526 CIA #2 in the C64 and C128 to the processor's NMI line, which was part of the means by which software emulation of the 6551 ACIA was accomplished. Atari's 8-bit line used a button for this same purpose. Debugging NMIs have appeared in a number of forms, including the Apple Macintosh's "programmers' button", and certain key combinations on Sun workstations. With the introduction of Windows 2000, Microsoft allowed the use of an NMI to cause a system to either break into a debugger, or dump the contents of memory to disk and reboot. Debugging NMIs have also been used by devices that allow leisure users and gamers to manipulate running programs. Devices which added a button to generate an NMI, such as Romantic Robot's Multiface, were a popular accessory for 1980s 8-bit and 16-bit home computers. These peripherals had a small amount of ROM and an NMI button. Pressing the button transferred control to the software in the peripheral's ROM, allowing the suspended program to be saved to disk (very useful for tape-based games with no disk support, but also for saving games in progress), screenshots to be saved or printed, or values in memory to be manipulated—a cheating technique to acquire extra lives, for example. Not all computers provide a mechanism for triggering NMIs; however, many machines (typically rackmount servers) provide a physical button specifically for this purpose. Other machines may expose this functionality via an expansion card. Miles Gordon Technology's DISCiPLE and +D products for the ZX Spectrum featured an NMI-producing "magic button". On the Nintendo Entertainment System, an NMI is generated during each vertical blanking interval. Because these NMIs (often referred to as "vblank interrupts") occur at frequent, regular intervals, code that manipulates game graphics and audio is often executed inside of the NMI handler routine.