these models with built-in keyboards. The 1000 RSX features two 16-bit AT ISA slots. Hard disk drives As hard disk drives at the time of the Tandy 1000's introduction were very expensive, Tandy 1000 systems are not usually equipped with hard drives. However, it is possible to add a hard drive to most Tandy 1000 computers. Most of the desktop-type Tandy 1000 units can accept regular 8-bit ISA bus MFM, RLL and SCSI controllers like typical XT-class machines; however, care has to be taken when configuring the cards so that they do not cause conflicts with the on-board Tandy-designed peripherals. For most Tandy 1000 models (other than the compact EX and HX) that do not come equipped with a hard drive, Tandy offered hard disk options in the form of hardcards that are installed in one of the computer's expansion slots and consist of a controller and drive (typically a 3.5-inch MFM or RLL unit with a Western Digital controller) mounted together on a metal bracket. Their own 20 MB hard card was offered for $799, though compatible third-party units were available. Although this arrangement providses a neat physical coupling between the controller and the disk, single-sector internal transfers and dependence on the speed of the host machine to transfer data to memory means that a trial-and-error approach was still needed to set the disk interleave correctly to ensure optimum transfer rates. Furthermore, as the Tandy 1000's slots are only 10.5" long and are 8-bit only, some units do not fit and/or operate correctly unless they are certified to be Tandy-compatible. Starting with the Tandy 1000 TL/2, XT IDE controllers are integrated onto the motherboard. However, these are incompatible with common AT IDE hard drives. The TL/2, TL/3, RL and RLX all use the XT IDE interface, where the later (and significantly upgraded) RSX is the only Tandy 1000 model computer to use a standard AT IDE interface. One option for modern users of these systems is to install and use XT ISA CompactFlash adapter; this is also the most practical way to install a hard drive into a Tandy 1000 EX or HX, using an adapter cable that adapts the male PLUS-style connector to an 8-bit ISA card-edge slot. I/O and ports Tandy 1000, SX, and TX use a proprietary 8-pin round DIN connector for the keyboard port that is compatible with the older TRS computers but not compatible