The DSC6121JI2A-0090: This dual-frequency part is useful where a board needs two close-but-distinct reference clocks without a second oscillator footprint — think a baseband plus a slightly offset sample clock, or a main controller plus a secondary peripheral that runs on a different crystal frequency.
Supplied in Tube — not tape-and-reel, so if your pick-and-place line expects reel feed, factor in a tube-to-reel transfer or hand-place for prototype runs.
Lifecycle reality — obsolete, sourced to order
No official successor order code is listed on the lifecycle record, meaning there is no drop-in replacement from Microchip with the same dual-frequency output in the same package. If you need this exact frequency pair and footprint, the surplus route is the only option; a board spin to a different oscillator is the alternative.