Atomic operations may be implemented on a processor system having a main memory and two or more processors including a power processor element (PPE) and a synergistic processor element (SPE) that operate on different sized register lines. A main memory address containing a primitive is divided into a parity byte and two or more portions, wherein the parity byte includes at least one bit. A value of the parity byte determines which of the two or more portions is a valid portion and which of them is an invalid portion. The primitive is of a memory size that is larger than a maximum size for atomic operation with the PPE and less than or equal to a maximum size for atomic operation with the SPE. Read with reservation and conditional write instructions are used by both the PPE and SPE to access or update a value of the atomic.