Why does pointer size appear 4 bytes on some system and 8 on others?

Pointers are potentially unsigned integers. Each number value corresponds to a particular location in RAM.

The size of the poitner depends on the architecutre of the system where 4 bytes are used to address 32 bit system and 8 bytes are used to address 64 bit systems.

When we say that a system is N-bit(16 bit or 32 bit or 64 bit) we mean to say the size that the system uses to store an integer value.

This is also the size of the poitner as mentioned it is an unsigned integer.

This is also the reason why a 32 bit system can have a maximum of