unidirectional parallel port instead of the edge-connector ports, and the SL's enhanced graphics and sound. A single half-size 8-bit expansion slot is available. The RL/HD has a battery-backed real-time clock chip to store date and time information, which the RL lacked. These models also has MS-DOS and a portion of DeskMate in ROM, and can therefore boot much faster than many other computers on the market. The RL/HD comes with a 20MB drive preinstalled. 1000 RLX The RLX is the 'mid-range' offering of the RL line. It has a 10 MHz 286 (surface-mounted) and 512 KB of RAM, and unlike other 286-based Tandy 1000 models, it supports 384 KB of extended memory when RAM is expanded to the maximum 1 MB. However, it is not a full AT-class machine, as it still has an 8-bit ISA bus (as with the RL, one half-size expansion slot) and only 8 IRQs and 4 DMA channels. While the three-voice sound chip and DAC are still present, Tandy video was dropped in favor of an AcuMos VGA controller offering 256 KB of video memory and standard VGA graphics resolutions. The parallel port is bidirectional, a first for the Tandy 1000 series. The RLX has one 1.44 MB 3.5" floppy drive; an empty drive bay can host a second such drive. The hard disk RLX/HD comes with a 20 MB hard disk and 1 MB RAM preinstalled. The hard disk occupies the empty drive bay, so this version supports only a single floppy drive. 1000 RSX A more upscale offering, the RSX offers a 25 MHz 80386SX processor, 1 MB RAM, two 16-bit ISA slots, AcuMos SVGA video, a bidirectional parallel port, and standard PS/2 keyboard and mouse ports. It is a full 386-class PC and can run Microsoft Windows 3.x. Two sockets for SIMM memory cards are available. Only 1 MB or 4 MB SIMMs of the 9-chip type are supported, and if two are installed they have to be of like capacity. With two 4 MB SIMMs installed, the 1000 RSX can be expanded to 9 MB RAM without using an ISA slot. The RSX/HD variant comes with a 52 MB hard drive using an AT-compatible IDE interface; replacement hard drives up to 504 MB can be substituted. Because of the slimline case, only one hard drive can be installed alongside the 1.44 MB 3.5" floppy drive. The motherboard hs a socket for