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CMOS inverter (a NOT logic gate). Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss ", / s iː m ɑː s /, /-ɒ s /) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFETs for logic functions. [1]
It is referred to as non-volatile memory or NVRAM because, after the system loses power, it does retain state by virtue of the CMOS battery. When the battery fails, BIOS settings are reset to their defaults. The battery can also be used to power a real time clock (RTC) and the RTC, NVRAM and battery may be integrated into a single component.
The first CMOS family of logic integrated circuits was introduced by RCA as CD4000 COS/MOS, the 4000 series, in 1968. Initially CMOS logic was slower than LS-TTL. However, because the logic thresholds of CMOS were proportional to the power supply voltage, CMOS devices were well-adapted to battery-operated systems with simple power supplies.
Memory cell; Memory coherence; Cache coherence; Memory hierarchy; Memory access pattern; Memory map; Secondary storage; MOS memory. floating-gate; Continuous availability
Later computers, including most IBM-compatibles with 80286 CPUs, had a battery-backed nonvolatile BIOS memory (CMOS RAM chip) that held BIOS settings. [48] These settings, such as video-adapter type, memory size, and hard-disk parameters, could only be configured by running a configuration program from a disk, not built into the ROM.
For example, IBM PC's and successors beginning with the IBM PC AT used nonvolatile BIOS memory, often called CMOS RAM or parameter RAM, and this was a common solution in other early microcomputer systems like the original Apple Macintosh, which used a small amount of memory powered by a battery for storing basic setup information like the ...
Later the decreased cost of the CMOS technology allowed the same devices to be fabricated using it, adding the letter "C" to the device numbers (27xx(x) are n-MOS and 27Cxx(x) are CMOS). While parts of the same size from different manufacturers are compatible in read mode, different manufacturers added different and sometimes multiple ...
CMOS memory was commercialized by RCA, which launched a 288-bit CMOS SRAM memory chip in 1968. [23] CMOS memory was initially slower than NMOS memory, which was more widely used by computers in the 1970s. [24] In 1978, Hitachi introduced the twin-well CMOS process, with its HM6147 (4 kb SRAM) memory chip, manufactured with a 3 μm process. The ...