The total number of all Apple computers in active use is growing rapidly, and is about to reach $ 1.5 billion. This includes Macs, iPhones and iPads.
That said, most of it is total iPhones. An industry analyst estimates there will be a billion of these in active use early next year.
These numbers come from Horace Dediu of Asymco.
According to trend lines, 1.5 billion active Apple devices will be in use by the end of September and 1 billion iPhones by the end of the year or Q1 2020. $ AAPL pic.twitter.com/J3u8u9Qdy7  – Horace Dediu (@asymco) August 1, 2019
Look at the red line on his chart to see growth in all Apple devices, and the purple line shows the increase in the iPhone.
Installed base vs. sales
While the number of iPhones sold each quarter receives a lot of attention, the total number of those in use is at least as important. The same goes for iPads and Macs. Older devices still contribute to Apple's top line because their users subscribe to Apple services and buy software.
That's why Apple's quarterly revenue (on the yellow Dediu map) is growing so fast, even though iPhone sales have slowed in recent quarters.
Apple executives continued to bring up this topic during the conference call with investors earlier this week. "Our active installed base of iPhone reached a new all-time high and was up year over year in each of our top 20 markets," says CEO Tim Cook. And CFO Luca Maestri said "The active installed Mac base again reached a new all-time high," and "the iPad-active installed base also reached a new all-time high."
Why the iPhone Installed Base Is Falling and Why It's Rising
During the revenue call, Cook discussed what could reduce the size of Apple's installed base, as well as the factors that keep it growing instead.
"Installed base is a function of upgrades and the time between them," he pointed out. This is an oblique reference to the growing time Apple customers are holding on to their handsets, slowing quarterly sales.
Cook went on to say that the installed base is also "a function of the number of switches coming to iOS, macOS and so on. It is a function of the robustness of the secondary market, which we find overwhelmingly hitting an incremental customer." refers to people who buy used iPhones.
"And there is still a feature in the emerging markets and somewhat developed markets to a lesser extent people buying their first smartphone," Cook noted. "There are still quite a few people in the world in that category."