Restricted platforms are computer platforms which the user has limited control over because of technical limitations, placed there either to intentionally limit the user or because of legitimate design considerations. In other words, such a platform retrains the user from accessing all the features of the device.
I have coined this term because I could not find a universal term for this concept. However, it is an important one to understand when choosing a platform. Contrast this concept with the Unrestricted Platform.
Restricted platforms include embedded systems, smartphones and tablets. All these are computer systems, and most of them are more powerful and have more resources than many past desktop personal computers. However, they are more limited in the sense that they do not allow the user full control of the system. For example, a 20-year-old desktop computer is far less powerful than a new iPhone or Android phone. But (provided that it is still functioning properly) you can install a new linux distro on that 20-year-old PC, but you can't change the Operating System on your smartphone or tablet. You may be able to control which programs send out data on the old PC, but you may not be able to do so on your tablet or smartphone.
In the past, many of the restrictions of these platforms have been because of legitimate design considerations for the practicality or usability of the device. For example, an older or simpler (non-smart) cellular phone requires specialized hardware and an embedded OS to be sufficiently small and energy efficient and small to be practical for the user.
However, the days of a myriad of specialized mobile platforms are largely gone and the design restrictions of yesteryear are no longer necessary from a legitimate design perspective. Instead, today's restricted platforms are designed as such in order to intentionally prevent the user from fully controlling their own device. There is no technical reason, for instance, that a smartphone cannot have a memory card slot or a removable battery. And if they wanted to, corporations could design a smartphone capable of running alternative operating systems easily. Nevertheless, this is not inline with their desire to limit and control users for their own profit and power.
While smartphone and tablets can be very convenient, because of their compact size and long battery life, be assured that if they are restricted platforms you will never be able to fully control and utilize this computer. There are some things that you will be prevented from doing, even if the device has the technical capabilities and resources to do so.
Desktops and laptops have traditionally been Unrestricted platforms and largely still are today. However, the trend is towards making these restricted platforms as well. Witness the appearance of Google Chromebooks, which unnecessarily restrict and spy on the user. Similarly, Secure Boot may restrict users on what OS they install on their desktops or laptops.
Many users interpret the increased speed, portability, resources and other capabilities of these devices as an improvement, without realizing that control of their devices is being subtly taken away from them and given to another entity (usually the corporation who sells the device) instead.