20 MB of storage. The LDOS operating system by Logical Systems was bundled, which provides utilities for managing the storage space and flexible backup. The initial retail price for the first (primary) unit (). Later, a 15MB hard disk was offered in a white case, which can be daisychained for up to 60 MB. Like most hard disks used on 8-bit machines, there is no provision for subdirectories, but the DiskDISK utility is a useful alternative that creates virtual hard disk ".DSK" files that can be mounted as another disk drive, and used like a subdirectory would. To display the directory/contents of an unmounted DiskDISK virtual disk file, a shareware DDIR "Virtual Disk Directory Utility" program was commonly used. Printers The "Quick Printer" is an electrostatic rotary printer that scans the video memory through the bus connector, and prints an image of the screen onto aluminum-coated paper in about one second. However, it is incompatible with both the final, buffered version of the Expansion Interface, and with the "heartbeat" interrupt used for the real-time clock under Disk BASIC. This can be overcome by using special cabling, and by doing a "dummy" write to the cassette port while triggering the printer. Two third-party printers were for metal-coated paper, selling for approximately DM 600 in Germany, and a dot-matrix printer built by Centronics for normal paper, costing at first DM 3000, later sold at approximately DM 1500 in some stores. It has only 7 pins, so letters with descenders such as lowercase "g" do not reach under the baseline, but are elevated within the normal line. Radio Shack offered an extensive line of printers for the TRS-80 family, ranging from basic 9-pin dot matrix units to large wide-carriage line printers for professional use, daisy-wheel printers, ink jet printers, laser printers and color plotters. All have a Centronics-standard interface and after the introduction of the Color Computer in 1980, many also had a connector for the CoCo's serial interface. FP-215 is a flatbed plotter. Software BASIC Three versions of the BASIC programming language were produced for the Model I. Level I BASIC fits in 4 KB of ROM, and Level II BASIC fits into 12 KB of ROM. Level I is single precision only and had a smaller set of commands. Level II introduced double precision floating point support and has a much wider set of commands. Level II was further enhanced when