block copy, block input/output (I/O), and byte search instructions. An overflow flag with better support for signed 8- and 16-bit arithmetics. New IX and IY index registers with instructions for direct base+offset addressing A better interrupt system: A more automatic and general vectorized interrupt system, mode 2, primarily intended for Zilog's line of counter/timers, DMA and communications controllers, as well as a fixed vector interrupt system, mode 1, for simple systems with minimal hardware (with mode 0 being the 8080-compatible mode). A non-maskable interrupt (NMI), which can be used to respond to power-down situations or other high-priority events (and allowing a minimalistic Z80 system to easily implement a two-level interrupt scheme in mode 1). A complete duplicate register file, which could be quickly switched, to speed up response to interrupts such as fast asynchronous event handlers or a multitasking dispatcher. Although they were not intended as extra registers for general code, they were nevertheless used that way in some applications. Less hardware required for power supply, clock generation and interface to memory and I/O Single 5-volt power supply (the 8080 needed −5 V, +5 V, and +12 V). Single-phase 5-volt clock (the 8080 needed a high-amplitude (9 to 12 volts) non-overlapping two-phase clock). Built-in DRAM refresh, which would otherwise require external circuitry, unless SRAM, more expensive and less dense (but faster), was used. Non-multiplexed buses (the 8080 had state signals multiplexed onto the data bus). A special-reset function that clears only the program counter, so that a single Z80 CPU could be used in a development system such as an in-circuit emulator. Success in the market The Z80 took over from the 8080 and its offspring, the 8085, in the processor market and became one of the most popular and widely used 8-bit CPUs. Some organizations such as British Telecom remained loyal to the 8085 for embedded applications, owing to their familiarity with it and to its on-chip serial interface and interrupt architecture. Likewise, Zenith Data Systems paired the 8085 with the 16-bit Intel 8088 in its first MS-DOS computer, the Zenith Z-100, despite having previous experience with its pioneering Z80-based Heathkit H89 and Zenith Z-89 products. However, other computers were made integrating the Z80 with other CPUs: the Radio Shack TRS-80 Model 16 with a Motorola 68000, the DEC Rainbow with an 8088, and the Commodore 128 with a MOS 8502. Zilog was later producing a low-power Z80 suitable