As per Apbr.org, the first free agency (restricted) started in 1980 with the compensation of cash, players or draft choices determined by the NBA Commissioner.
A restricted free agent's original team has the chance to keep the player by matching the offer sheet signed with another team. This is known as the "right of first refusal."
An unrestricted free agent is able to sign with any team he chooses. This became official in 1988.
Today, free agency is a given. According to Foxsports.com, when Tom Chambers made the leap from Seattle to Phoenix in 1988 it was anything but that. Chambers became the first player in the NBA to move from one team to another via unrestricted free agency. A door was opened that has changed the face of the sport.
The NBA's 2016 free agency period has been long anticipated because of the massive jump in salary cap from $70 million to a number now projected to be $94 million. Most teams around the league will be flush with cap space and looking to throw big dollars around, which will result in eye-popping contracts for a number of players. Find out more at Sbnation.com.