"From a personal point of view it was very difficult indeed, I still think this is the best job in the industry, but I have given my reasons for leaving. I've spent 12 years as CEO and as we think about the next stage and the five to eight year journey we're about to set off on, if I was still CEO then I don't think there would be sufficient edginess and energy in the executive team.
"I think it's the right thing to step back and allow change to happen."
Of course, given his passion for the company, it would be easy to fall back into a consulting role and keep an involvement, but East is not looking for an active role.
"As a shareholder I'll remain very interested, but I think part of the idea is to step back and allow proper proper change. In 1994 ARM was a startup with great potential and when I became CEO it was a very successful startup with great potential in the mobile space.
"We've scaled business way beyond mobile now, with 5 billion non mobile chips shipping this year we've scaled the operation to cope with multiple designs at the same time.
"From a business point of view we now have a sustainable long-term and very high-quality business. ARM is growing up and that is great fun."
ARM's profile remains a hot topic, and East admits it would be nice to be better known.
"It would be very nice to wander down the high street and be able to see all the ARM powered products, and I would be much more satisfied if my mother knew what an ARM product was but it doesn't necessarily help the business," he said.
"Seven or eight years ago you would never see ARM's financial reports on the BBC website and now you do."
ARM is headquartered in Britain with just under half of the workforce in the UK offices, and it is something that East believes is a huge benefit to the company. "It makes us different from most other technology companies - and that gets us more visibility," he concluded.