Greenwood's first instrument was a recorder given to him at age four or five. He took the instrument seriously, playing it into adulthood, and played baroque music in recorder groups as a teenager. He also learnt the viola and joined the Thames Vale youth orchestra, which he described as a formative experience: "I'd been in school orchestras and never seen the point. But in Thames Vale I was suddenly with all these 18-year-olds who could actually play in tune. I remember thinking: 'Ah, that's what an orchestra is supposed to sound like!'" Greenwood spent time as a child programming computers, experimenting with BASIC and simple machine code to build "rubbishy computer games". According to Greenwood, "the closer I got to the bare bones of the computer, the more exciting I found it".