16-bit computing

16-bit microcomputers are microcomputers that use 16-bit microprocessors. A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two most common representations, the range is 0 through 65,535 (216 − 1) for representation as an (unsigned) binary number, and −32,768 (−1 × 215) through 32,767 (215 − 1) for representation as two's complement. Since 216 is 65,536, a processor with 16-bit memory addresses can directly access 64 KB (65,536 bytes) of byte-addressable memory. If a system uses segmentation with 16-bit segment offsets, more can be accessed. The MIT Whirlwind ( 1951) was quite possibly the first-ever 16-bit computer. It was an unusual word size for the era; most systems used six-bit character code and used a word length of some multiple of 6-bits. This changed with the effort to introduce ASCII, which used a 7-bit code and naturally led to the use of an 8-bit multiple which could store a single ASCII character or two binary coded decimal digits. The 16-bit word length thus became more common in the 1960s, especially on minicomputer systems. Early 16-bit computers ( 1965–70) include the IBM 1130, the HP 2100, the Data General Nova, and the DEC PDP-11. Early 16-bit microprocessors, often modeled on one of the mini platforms, began to appear in the 1970s. Examples ( 1973–76) include the five-chip National Semiconductor IMP-16 (1973), the two-chip NEC μCOM-16 (1974), the three-chip Western Digital MCP-1600 (1975), and the five-chip Toshiba T-3412 (1976). Early single-chip 16-bit microprocessors ( 1975–76) include the Panafacom MN1610 (1975), National Semiconductor PACE (1975), General Instrument CP1600 (1975), Texas Instruments TMS9900 (1976), Ferranti F100-L, and the HP BPC. Other notable 16-bit processors include the Intel 8086, the Intel 80286, the WDC 65C816, and the Zilog Z8000. The Intel 8088 was binary compatible with the Intel 8086, and was 16-bit in that its registers were 16 bits wide, and arithmetic instructions could operate on 16-bit quantities, even though its external bus was 8 bits wide.