Tandy 1000, the EX and HX do not have a built-in DMA controller, though one can be added using the PLUS memory expansion board. 1000 EX The Tandy 1000 EX features a 5.25" floppy drive built into the right-hand side of computer casing. The EX sold for US$1,000 from Radio Shack in December 1986. The EX and, later, the HX were among the most popular of the Tandy 1000 line because of their low price. A useful feature for the EX and later systems is the ability to boot off either drive, as the drives can be logically swapped when the system booted, so that the drive that was normally drive B: becomes drive A:, and vice versa, and the drives remain swapped until the system is powered off or reset. (The SX and TX have this capability as well.) The 1000 EX comes with MS-DOS 2.11 and Personal Deskmate on 5.25" 360 KB diskettes. The MS-DOS is a version specialized for and only bootable on the Tandy 1000; it includes a version of BASICA (Microsoft's Advanced GW-BASIC) with support for the enhanced CGA graphics modes (a.k.a. Tandy Graphics or TGA) and three-voice sound hardware of the Tandy 1000. 1000 HX The Tandy 1000 HX is an updated version of the EX, released in 1987. It utilizes the same architecture and PLUS cards as the EX, but with two 3.5" bays on the front panel, occupied by one or two 720 KB 3.5" floppy drives, as opposed to a single side-mounted 5.25" bay and floppy drive. It also has Tandy MS-DOS 2.11R in ROM, which can be accessed by starting the computer with no bootable disk. Another improvement over the EX is the addition of a serial EEPROM to store configuration information, enabling similar functionality to later CMOS NVRAMs. By comparison, earlier Tandy 1000 models, like IBM PC and PC/XT systems, use DIP switches and jumpers for startup configuration settings. By putting the basic elements of DOS and DeskMate in ROM and eliminating the memory test on startup, the HX boots quickly compared to other contemporary MS-DOS machines, despite having no immediate provisions for a hard disk drive. In addition to Tandy MS-DOS 2.11R, the HX shipped with Personal Deskmate 2. Most versions of MS-DOS works with the 1000 HX, including DOS 3.x and some later versions; DOS 4.0 is incompatible, and the installer for MS-DOS 6 can corrupt the