a window in the range between segments 0xA0000 and 0xBFFFF in the PC's real mode address space (A000:0000 and B000:FFFF in segment:offset notation). Typically, these starting segments are: 0xA0000 for EGA/VGA graphics modes (64 KB) 0xB0000 for monochrome text mode (32 KB) 0xB8000 for color text mode and CGA-compatible graphics modes (32 KB) Due to the use of different address mappings for different modes, it is possible to have a monochrome adapter (i.e. MDA or Hercules) and a color adapter such as the VGA, EGA, or CGA installed in the same machine. At the beginning of the 1980s, this was typically used to display Lotus 1-2-3 spreadsheets in high-resolution text on a monochrome display and associated graphics on a low-resolution CGA display simultaneously. Many programmers also used such a setup with the monochrome card displaying debugging information while a program ran in graphics mode on the other card. Several debuggers, like Borland's Turbo Debugger, D86 and Microsoft's CodeView could work in a dual monitor setup. Either Turbo Debugger or CodeView could be used to debug Windows. There were also DOS device drivers such as ox.sys, which implemented a serial interface simulation on the monochrome display and, for example, allowed the user to receive crash messages from debugging versions of Windows without using an actual serial terminal. It is also possible to use the "MODE MONO" command at the DOS prompt to redirect the output to the monochrome display. When a monochrome adapter was not present, it was possible to use the 0xB000–0xB7FF address space as additional memory for other programs. Programming "Unchaining" the 256 KB VGA memory into four separate "planes" makes VGA's 256 KB of RAM available in 256-color modes. There is a trade-off for extra complexity and performance loss in some types of graphics operations, but this is mitigated by other operations becoming faster in certain situations: Single-color polygon filling could be accelerated due to the ability to set four pixels with a single write to the hardware. The video adapter could assist in copying video RAM regions, which was sometimes faster than doing this with the relatively slow CPU-to-VGA interface. The use of multiple video pages in hardware allowed double buffering, triple buffering or split screens, which, while available in VGA's 320×200 16-color mode, was not possible using stock Mode 13h. Most particularly, several higher, arbitrary-resolution display modes were possible, all the way up to the programmable