In 1977, a 21-year-old Steve Jobs unveiled something the world had never seen before: a ready-to-program personal computer. After powering the machine up, proud Apple II owners were confronted with a cryptic blinking cursor, awaiting instructions.

The Apple II was a clean slate, a device built – boldly – with no specific tasks in mind. Yet, despite the cursor, you did not have to know how to write programs. Instead, with a few keystrokes you could run software acquired from anyone, anywhere. The Apple II was generative. After the launch, Apple had no clue what would happen next, which meant that what happened was not limited by Mr Jobs’ hunches. Within two years, Dan Bricklin and Bob Frankston had released VisiCalc, the first digital spreadsheet, which ran on the Apple II. Suddenly businesses around the world craved machines previously marketed only to hobbyists. Apple IIs flew off the shelves. The company had to conduct research to figure out why.

Thirty years later Apple gave us the iPhone . It was easy to use, elegant and cool – and had lots of applications right out of the box. But the company quietly dropped a fundamental feature, one signalled by the dropping of “Computer” from Apple Computer’s name: the iPhone could not be programmed by outsiders. “We define everything that is on the phone,” said Mr Jobs. “You don’t want your phone to be like a PC. The last thing you want is to have loaded three apps on your phone and then you go to make a call and it doesn’t work any more.”

The openness on which Apple had built its original empire had been completely reversed – but the spirit was still there among users. Hackers vied to “jailbreak” the iPhone, running new apps on it despite Apple’s desire to keep it closed. Apple threatened to disable any phone that had been jailbroken, but then appeared to relent: a year after the iPhone’s introduction, it launched the App Store. Now outsiders could write software for the iPhone, setting the stage for a new round of revolutionary VisiCalcs – not to mention tens of thousands of simple apps such as iPhone Harmonica or the short-lived I Am Rich, which for $999.99 displayed a picture of a gem, just to show that the iPhone owner could afford the software.

But the App Store has a catch: app developers and their software must be approved by Apple. If Apple does not like the app, for any reason, it is gone. I Am Rich was axed from the Store after it was ridiculed in the press. Another app, Freedom Time, never made it in. It counted down the days to the end of George W. Bush’s US presidency, and that was deemed too politically sensitive. An e-mail reader was denied because it competed with Apple’s own Mail app. Imagine if Microsoft’s Bill Gates had decreed that no other word processor but Word would be allowed to run on the Windows operating system. Microsoft lost a decade-long competition lawsuit for far less proprietary behaviour.

Despite outsiders being invited to write software, the iPhone thus remains tightly tethered to its vendor – the way that the Kindle is controlled by Amazon. George Orwell’s 1984 was retroactively zapped from Kindles around the world after Amazon grew concerned that it had sold the book without permission.

To be sure, many rejected apps will not be missed. (Only eight spendthrifts bought I Am Rich before it disappeared.) And users can be protected from harmful software from suspect sources. But consider: the world wide web started as, and remains, an app. Its first versions were written by Tim Berners-Lee, a British computer scientist who was unaffiliated with any software or hardware vendor. How worthy of approval would Wikipedia have seemed when it boasted only seven articles – dubiously hoping that the public would magically provide the rest? How threatened might today’s content publishers feel by peer-to-peer apps that let iPhone users trade data from one phone to another? We know the answer to that: enough that they have persuaded Apple to exclude all such apps from the App Store.

It is tempting to think that a little outside software is better than none. But what is fine for a single device may be bad for the ecosystem. The iPhone’s hybrid model of centrally controlled outside software is already moving beyond the smart phone. This is the significance of the iPad. It could have been built either like a small Apple Macintosh – open to any outside software – or as a big iPhone, controlled by Apple. Apple went with the latter. Attach a keyboard to it and it could replace a PC entirely – boasting plenty of new apps, but only as Apple deems them worthy.

If Apple is the gatekeeper to a device’s uses, the governments of the world need knock on the door of only one office in Cupertino, California – Apple’s headquarters – to demand changes to code or content. Users no longer own or control the apps they run – they merely rent them minute by minute.

Hope lies in more balanced combinations of open and closed systems, such as that embodied by the traditional Apple Mac – or phones based on the Android operating system from the Open Handset Alliance, a consortium of hardware, software and telecoms companies. Android Market is the approved counterpart to Apple’s App Store but, in this case, users are also free to go off-roading, installing any code they like. Android is a canary in the digital coal mine: will its more open model survive should people load suspect apps and find they cannot make calls any more?

Mr Jobs ushered in the personal computer era and now he is trying to usher it out. We should focus on preserving our freedoms, even as the devices we acquire become more attractive and easier to use.

The writer is professor of law at Harvard Law School and a founder of its Berkman Center for Internet & Society. He is author of The Future of the Internet – and How to Stop It