Illumina sells the instruments that read DNA, along with the reagents and flow cells those instruments consume with every run. That split matters more than the hardware headline: an installed sequencer generates recurring consumable revenue for years, so the size and utilisation of the installed base drives the business more than instrument sales in any given period. Customers span academic research, pharmaceutical development and clinical diagnostics, which means demand is tied to research funding cycles and to how quickly sequencing moves from the laboratory into routine medical use. Rival platforms have narrowed what was once a near monopoly on high throughput sequencing.