with the IBM PC/AT or PS/2 standard. Some scan codes differ between the Tandy 1000 and IBM PC/XT and AT, resulting in software compatibility issues. The SL/TL and later use a more directly PC/XT-compatible keyboard protocol, and the 1000 RSX used a PC/AT and PS/2-compatible protocol. Tandy 1000 uses a proprietary 6-pin female round connector for the joystick port that on the SX/TX i adjacent to the keyboard port in the front of the computer. As with the keyboard, it is compatible with the older TRS-80 and Tandy color computer models, but not compatible with the IBM standard 15-pin male game port. Some DOS games do not work with these joystick ports, but those that support Tandy 1000 graphics and sound work. Early Tandy 1000 models use a non-standard card-edge parallel printer port rather than industry standard DB-25 printer port. It requires a Tandy-1000 compatible printer cable to connect to a standard printer parallel port. This was later changed to a standard DB-25 connector on the 1000 RL. Tandy 1000TX and beyond use a proprietary floppy drive cable port, that also powers the floppy drive. It requires a Tandy 1000-compatible floppy drive, though it may be possible to modify a floppy drive cable to make a standard floppy drive work. Operating systems and environments Tandy shipped PCs with their own customized version of MS-DOS, which are compatible with Tandy graphics and keyboard. The most current version of MS-DOS for Tandy 1000 is DOS 3.22. Tandy 1000s came shipped with one of several varieties of DeskMate, the company's own GUI productivity software suite. There may be compatibility issues with later versions of DOS such as DOS 5 and DOS 6. Until the 1000 RLX, Tandy 1000s are typically limited to 640 KB main memory, and non-Tandy versions of DOS often reduce the memory available for applications and games. In addition, the hardware detection routine for the installer of Microsoft MS-DOS 6 can corrupt the serial EEPROM of Tandy 1000 HX machines. Tandy 1000s can work with Windows 1.0, 2.0, and 3.0 but not 3.1, with the exception of the RLX which can run Windows 3.1 in Standard mode, and the RSX which fully supports Windows 3.1 in 386 Enhanced mode. Peripherals Monitors Tandy offered two color monitors specific for its Tandy 1000 computers: the CM-5, with a 0.64 millimeter dot pitch, and the Tandy CM-11 with a dot pitch of 0.42