which take type 4116 DRAMs, so memory configurations come in 16 KB, 32 KB, or 48 KB RAM memory sizes. Computers with 32 KB or 48 KB RAM can be upgraded with floppy disk drive storage. There is space inside the computer cabinet for two full-height drives. Those offered by Tandy/Radio Shack are single-sided, 40 track, double-density (MFM encoding) for 180K of storage. Third-party suppliers offered double-sided and 80-track drives, though to control them they had to modify the TRSDOS driver code or else furnish an alternative third-party DOS which could (see below). The installation of floppy disk drives also requires the computer's power supply to be upgraded. There is no internal cooling fan in the Model III; it uses passive convection cooling (unless an unusual number of power-hungry expansions were installed internally, such as a hard disk drive, graphics board, speedup kit, RS-232 board, etc.). Tandy claimed that the Model III was compatible with 80% of Model I software. Many software publishers issued patches to permit their Model I programs to run on the Model III. Marketing director Ed Juge explained that their designers considered changing from the Model I's 64 column by 16 row video screen layout, but that they ultimately decided that maintaining compatibility was most important. The Model III's memory map and system architecture is mostly the same as the Model I, but the disk drives and printer port were moved from memory mapped to port I/O, thus Model I software that attempts to manipulate the disk controller directly or output to the printer (in particular Model I DOSes and application packages such as Visicalc and Scripsit) will not work. Under the supplied TRSDOS 1.3 operating system Model I disks can be read in the Model III, but not vice versa. The optional LDOS OS (by Logical Systems Inc.) use a common disk format for both Model I and Model III versions. Customers and developers complained of bugs in the Model III's Microsoft BASIC interpreter and TRSDOS. Tandy/Radio Shack (and TRS-80 magazines like 80 Micro) periodically published many software patches to correct these deficiencies and to permit users to customize the software to their preferences. Differences in the WD1771 and WD1791 floppy controllers created problems reading Model I disks on a Model III (the double-density upgrade in the Model I include both chips while a Model III had only the WD1791). The WD1771 supports four data