The Indian Administrative Service (IAS) is the administrative arm of the All India Services.[3] Considered the premier civil service of India,[3][4] the IAS is one of the three arms of the All India Services along with the Indian Police Service (IPS) and the Indian Forest Service[citation needed] (IFS). Members of these three services serve the Government of India as well as the individual states. IAS officers may also be deployed to various public sector undertakings. As with other countries following the Westminster parliamentary system of government, the IAS is a part of the permanent bureaucracy of the nation,[5] and is an inseparable part of the executive of the Government of India. As such, the bureaucracy remains politically neutral and guarantees administrative continuity to the ruling party or coalition.[5] Upon confirmation of service, an IAS officer serves a probationary period as a sub-divisional magistrate. Completion of this probation is followed by an executive administrative role in a district as a district magistrate and collector which lasts several years, as long as sixteen years in some states. After this tenure, an officer may be promoted to head a whole state division, as a divisional commissioner. On attaining the higher scales of the pay matrix, IAS officers may lead government departments or ministries. In these roles, IAS officers represent the country at the international level in bilateral and multilateral negotiations +HISTORY BOOK