Cache logic: A trademark of Atmel Corp., cache logic refers to the ability of some Atmel FPGAs to store several logic configuration files on the chip, and to substitute one configuration for another very quickly, without transferring new configuration data in from an external memory. This permits the chip to reconfigure itself on the fly in response to context switches or even changes in the incoming data stream. That, in turn, lets a single FPGA implement more logic than it could hold at one time.

Embedded FPGA: This term is a dual misnomer: referring neither to embedded computing applications nor, strictly speaking, to FPGAs. Embedded FPGA is the most common term to describe an array of field-programmable logic that is embedded within an otherwise fixed system-level IC. Generally this block is provided as a hard macro, although exceptions have been proposed, and does not contain all of the supporting circuitry that would be necessary in a standalone FPGA. It may also use radical approaches to interconnect and/or logic cells that the developers deem more appropriate to a macro within a larger chip.

Programmable: This word has been appropriated by so many special interests that it has ceased to be much more than punctuation. It carries the general sense of "configurable by means of volatile data." More specifically, "programmable" can refer to a CPU-based system programmed by creating microprocessor code, or to a state machine programmed by defining the state transitions (probably the original meaning, from relay-based control systems) or to "programmable logic" whose function and topology are determined by external data (either only once, or at power-up, or at any time). Untangling exactly what is meant in a given context can be challenging. See "software-defined radio."

Reconfigurable: Another word that seems perfectly clear, but that has been appropriated until stretched beyond its elastic limit. Depending on the vendor, "reconfigurable" can mean that the system in question can be reconfigured at will during operation, or that it can be halted and reconfigured, or that it can be reconfigured only at power-up, or that it can be configured only once, either at time of manufacture or, in the case of some CPU cores, at time of original design. The distinction between these meanings can be profound in many applications.

Reconfigurable computing: This phrase represents a special use of the word "reconfigurable." Properly, it refers to a line of inquiry that has been going on for a number of years, researching the properties of computing systems that can alter their hardware configuration in response to changing context or data content. Research so far has shown that reconfigurable computing techniques when applied to some problems can yield substantial increases in both performance and substantial energy and hardware savings. Experience has also cautioned that in many cases development of such systems can be extraordinarily demanding.

Software-defined radio: another deceptively clear-sounding phrase. One would assume that software-defined radio would refer to a radio in which the operating characteristics were defined by software-that is, a radio in which the fundamental data transforms were executed by running software on DSPs or CPUs. However, the industry has chosen to understand a very loose definition of "software" and a very rigid definition of "defined." Hence the term has come to mean simply that some form of volatile data-the software-determines the configuration of the hardware in the radio.

Thus SDR can mean a radio in which all the demodulation, data recovery, error correction, and even much of the filtering is done in real time by DSPs. Or it can mean a radio implemented entirely in dedicated hardware, in which some of the hardware configuration or functionality can be altered by means of a configuration bit-stream.