good. As memory production yields improved and costs went down, many (perhaps most) 32K CoCo 1s shipped with perfectly good 4164 memory chips. Utilities and programs began to take advantage of the hidden 32K. Users opening the case risked invalidating the warranty. Radio Shack could upgrade all versions that shipped with standard Color BASIC to Extended Color BASIC, developed by Microsoft, for $99. BYTE wrote in 1981 that through Extended Color BASIC, Radio Shack "has released the first truly easy-to-use and inexpensive system that generates full-color graphics". Eventually the 32K memory option was dropped entirely and only 16K or 64K versions were offered. In late 1982, a version of the Color Computer with a white case, called the TDP System 100, was distributed by RCA and sold through non-Tandy stores. Except for the nameplate and case, it is identical to the Color Computer. Later, both the CoCo and the TDP System 100 shipped with a white case with ventilation slots running the length of the case rather than only the sides. This ventilation scheme carried over to the CoCo 2. Some late versions of the CoCo have a modified keyboard, often referred to as the "melted" keyboard, with bigger keycaps. Peripherals included tape cassette storage, serial printers, a 5.25-inch floppy disk drive, a pen and graphics tablet called the X-Pad, speech and sound generators, and joysticks. Color Computer 2 (1983–1986) During the initial CoCo 1 production run, much of the discrete support circuitry had been re-engineered into a handful of custom integrated circuits, leaving much of the circuit board area of the CoCo 1 as empty space. To cut production costs, the case was shortened by about 25% and a new, smaller power supply and motherboard were designed. The "melted" keyboard from the white CoCo 1 and the TDP-100 style ventilation slots were carried over. Aside from the new look and the deletion of the 12 volt power supply to the expansion connector, the computer was compatible with the previous generation. The removal of the 12V power supply crippled some peripherals such as the original floppy disk controller, which then needed to be upgraded, installed in a Multi-Pak interface, or supplied with external power. The CoCo 2 was sold in 16K and 64K models. 16K models use 16Kx1 DRAMs, but the chips are not the common 4116; they were instead 4517s (Radio Shack P/N 8040517), which use only +5V power