. Because the slots are inches in length instead of the PC's 13 inches, full-length cards do not fit, but reviewers noted that the many built-in hardware features reduce the need for cards. A later revision of the original Tandy 1000 model is the Tandy 1000A. This revision fixed bugs, scans expansion cards for bootable ROMs, and adds a socket for an Intel 8087 math coprocessor. Tandy 1000 HD The original Tandy 1000 (and many other models), like most home computers sold at the time, does not have a hard disk drive. The Tandy 1000 HD is essentially an original Tandy 1000 with a hard disk option factory installed. The factory hard disk has a capacity on the order of 10 or 20 MB. Tandy 1000 SX and TX The Tandy 1000 SX and TX are upgraded versions of the original Tandy 1000, utilizing a similar chassis. Two major upgrades over the original Tandy 1000 are the inclusion of a DMA controller, which improved the speed of diskette operations and IBM PC-compatibility of these systems, and the addition of two additional ISA expansion slots, to offer a total of five 8-bit ISA slots. 1000 SX The Tandy 1000 SX uses a 7.16 MHz 8088-2 processor, has 384 KB of memory (upgradeable to 640 KB on the motherboard), comes with either one or two 5.25" internal floppy disk drives, and has the light pen port (not a serial port) like the original Tandy 1000. An adjustable potentiometer inside the system controls the volume of the internal speaker. The Tandy AX is an SX rebadged for sale in Walmart stores. The 1000 SX comes with MS-DOS 3.2 and DeskMate II on 5.25" 360 KB diskettes. The SX is the first Tandy 1000 in which the built-in video circuitry can be disabled via DIP switch. This is to permit the installation of an upgraded graphics card, typically an EGA or VGA card, in an expansion slot. 1000 TX The Tandy 1000 TX is similar to the 1000 SX with its detached keyboard, unique parallel port edge connector, and XT-style architecture in a slightly modified case. The major difference is the 80286 CPU clocked at 8 MHz. It features a 16-bit-wide memory bus, although the on-board peripherals and ISA slots are 8 bits wide. The TX has a 3.5" internal floppy disk drive mounted in a 5.25" bay with room for an optional second