4level

4level is a term used in several technical contexts to denote configurations or schemes that rely on four distinct states or levels. It is not a single widely adopted specification but a descriptive label that appears in areas such as digital communications and storage technology.

In digital communications, four-level signaling refers to modulation schemes that encode information with four discrete signal levels. The most common example is PAM-4, which uses four amplitude levels to represent two bits per symbol. PAM-4 enables higher data rates over limited bandwidth, but introduces greater sensitivity to noise and requires more complex equalization and decoding.

In flash memory, a four-level cell (often described as multilevel cell or MLC) uses four distinct threshold voltage levels per cell to store data, typically encoding two bits per cell. This approach increases storage density compared with single-level cells but generally reduces endurance, write speed, and retention, demanding careful error correction and wear leveling.

Other uses of the term are context-dependent and may describe four-tier architectures, four-level decision processes, or ordinal scales in classification tasks.