Memory is always, by definition, a scarce resource on any software platform. But when it comes to mobile devices, this is an even more constrained resource. Mobile devices often have less physical memory and processor capacity that their bigger peers, and having an efficient memory management is crucial to improving user experience and software stability.
Dalvik Virtual Machine routinely triggers garbage collection in a similar way to Java, but this does not mean that we can ignore memory management completely. One very common error in junior programmers is to create memory leaks. A memory leak happens when an object is stored in memory, but it cannot be accessed anymore by the running code. The size can vary a lot (from an integer to a big bitmap or structure of several megabytes), but in general they affect software smoothness and integrity. We can use automated tools and frameworks to detect memory leaks and also apply some programming techniques to avoid allocating objects unnecessarily (and equally important, to deallocate them when they are no longer needed).
An Android application has a maximal amount of RAM memory that it can manage. It is different for each device (yes, another problem of the system fragmentation), and can be particularly checked by calling the function getMemoryClass() on the ActivityManager. Early devices had a per-app cap of 16 MB. Later devices increased that to 24 MB or 32 MB, and it will not be surprising to see devices up to 48 or 64 MB. There are several factors contributing to this fact, such as screen size. Larger screens generally mean larger resolutions for bitmaps; thus, as they increase, memory requirements will also grow. Some techniques can also bypass this limitation, such as using the NDK or requesting from the system a larger heap. This last is, however, considered to be poor form for an Android app.
When a process starts, it is forked from an existing or root process called Zygote. Zygote starts every time the system boots and loads the resources common to all the apps. By doing this, Android tries to share all the common resources among the applications, avoiding duplicating memory usage for the same frameworks.
