What is the difference between a garbage collector and reference counting?

Garbage Collector (GC) and Reference Counting are two different mechanisms of automatic memory management.

Reference Counting:

• Each object is associated with a counter that increases when a new reference to the object is created and decreases when a reference is deleted.
• When the counter reaches zero, the object is immediately freed.
• Simple and predictable mechanism.
• The main drawback is that it cannot detect cyclic references (when objects refer to each other but are not used externally), which can lead to memory leaks.

Garbage Collector:

• Periodically scans memory to determine which objects are reachable from root references (e.g., stack, global variables).
• Objects that are not reachable are considered garbage and are removed.
• Allows detection and removal of cyclic references.
• May cause pauses in program execution (depending on implementation).

In iOS, for example, reference counting with automatic management (ARC) is used, which compiles code to manage reference counters, and weak references and other techniques are used to solve the problem of cycles.