All India Services and Central Services
Union Public Service Commission(UPSC) conducts examination to select officers to serve in various services. These services are broadly classified into All India Services and Central services.
All India Services
There are three All India Services
1. Indian Administrative Service (IAS)
2. Indian Police Service (IPS)
3. Indian Forest Service (IFS).
These three services have common preliminary examination under Civil Services Examination. Indian Forest Service (IFS) has separate main examination. IAS and IPS have common main Civil Services Examination.
All India Service officers are posted in a particular cadre or state. They function under that particular cadre or state. They are transferred within that state/cadre. Sometimes they may serve in central secretariat in New Delhi under deputation.
Central Services
There are various central services.
1. Indian Revenue Service (IRS : Income Tax) Group A
2. Indian Revenue Service (IRS : Customs & Central Excise) , Group A
3. Indian Information Service (IIS) Group A
4. Indian Postal Service(IPoS) Group A
5. Indian Defence Estates Service(IDES) Group A
6. Indian Defence Accounts Service(IDAS) Group A
7. Indian Civil Accounts Service(ICAS) Group A
8. Indian Railway Traffic Service(IRTS) Group A
9. Indian Railway Accounts Service(IRAS) Group A
10. Indian Railway Personnel Service(IRPS) Group A
11. Indian Trade Service(ITS) Group A
12. Indian Company Law Service (ICLS) Group A
13. Indian P & T Accounts & Finance Service , Group A
14. Indian Audit and Accounts Service (IAAS), Group A
15. Indian Ordnance Factories Service, Group A
16. Indian Railway Protection Force (IRPF) , Group A

These e services have common preliminary and main examination under Civil Services Examination
The Central services do not have specific cadre/ state. The officers of thee services function under central government. They are posted all over the country and transferred anywhere in the country.