Last week, we were thrilled to introduce new iPads featuring the A7 chip with 64-bit desktop class architecture, ultrafast wireless, and expanded LTE connectivity.
The new iPad Air features a beautiful Retina Display in an elegant uni-body design that is 20% thinner and 28% lighter than the 4th generation iPad and the iPad mini with Retina Display packs all the pixels of the iPad Air into its stunning 7.9 inch display and runs over 475,000 iPad Apps available on the App Store.
Turning to Mac, sales of 4.6 million Macs were above our expectations, which is a 7% decline from the year ago quarter. IDC estimates the global personal computer market contracted by 10% during the September quarter, indicating that Macs continue to gain share just as they have for 29 of the last 30 quarters. We were especially pleased with strong year-over-year growth in sales of MacBook Air which we updated in June. In late September we updated iMac with 4th generation Intel quad core processors, new graphics, next generation Wi-Fi and faster PCI-E flash storage options.
Last week we launched new versions of MacBook Pro with Retina Display featuring 4th generation Intel core processors, faster graphics, long great battery life and a more affordable price. Also last week we launched Mavericks, the 10th major release of OS X with more than 200 new features. Mavericks brings iBooks and Maps to the Mac, includes a new version of Safari, enhances multi-display support, introduces Finder Tabs & Tags and delivers core technologies for breakthrough power efficiency and performance and is now free.
We ended the quarter with Mac channel inventory that was just below our four to five week target range. We continue to be very pleased with the growth of iTunes software and services and the strength of the Apple ecosystem. Our iTunes Stores generated record billings of $4.4 billion in the September quarter, thanks to continued strong growth in sales of Apps.
The quarter's iTunes billings translated to quarterly iTunes revenue of $2.4 billion, up 15% from the year ago quarter. The strong iTunes sales combined with other software and service revenue, resulted in total quarterly revenue of $4.3 billion from iTunes software and services, an increase of 22% year-over-year. Cumulative app downloads have reached 60 billion and our app developers have now earned $13 billion from sales through the App Store, half of which they've earned in the last year.
We had a tremendously successful launch of iOS 7 last month, with hundreds of millions of downloads in the first few days alone, making it the fastest software upgrade ever. Last week, we reported nearly two-thirds of iOS devices were already running iOS 7. That's significantly higher than the percentage of users running the latest versions of other mobile operating systems. This rapid transition to the latest version of iOS not only means that more customers are having the most advanced experience possible, but it also enables developers to offer their latest app innovations to hundreds of millions of users in a single software release.