From the Summary: "This report answers common questions related to federal retirement plans. The vast majority of the civilian federal workforce is covered by either the Civil Service Retirement System (CSRS) or the Federal Employees' Retirement System (FERS), depending on date of entrance into federal service. Most civilian federal employees hired before 1984 are covered by CSRS; most civilian federal employees hired in 1984 or later are covered by FERS. This FAQ [Frequently Asked Questions] focuses on policy issues related to CSRS and FERS while also identifying additional retirement plans that provide benefits to specific populations of civilian federal employees. It provides the legislative history of CSRS and FERS as well as information on benefits and financing."
CRS Report for Congress, R47084
Congressional Research Service: https://crsreports.congress.gov/