Microsoft CEO Satya Nadella recently said he wants to eventually see Windows 10 installed on a billion devices by 2018. The operating system, formally released July 29, is nowhere close to that yet -- but it is off to a good start.

Windows 10 has been installed on 18.5 million machines so far, according to tech blog Neowin. At one point, Windows 10 was seeing 1,500 installs per second. Microsoft sources speaking to Neowin said a previously-reported number of 67 million installations was incorrect.

Windows 7, by comparison, sold 240 million copies in its first year. Microsoft reported 14 million Windows 10 installations took place in the first 24 hours.

Windows 10 has received generally positive reviews. The OS is meant to provide a consistent user experience across PCs, tablets and smartphones. Microsoft's hope is that multi-platform support will appeal to mobile developers, a group that to date has focused mostly on writing apps for Android and iOS devices.