The Ibanez Radius series or "R series" was first launched in 1987 with the introduction of the Ibanez 540R where the R stands for Radius. Originally the Ibanez 540R together with the Ibanez 540S (Saber) and the Ibanez 540P (Power) were part of the Roadstar (II)Pro 540 series. 
The Ibanez 540R was therefore also known as the Ibanez PRO540R, later in 1992 the more common "series name + model number" model was introduced for the Radius series.
The Ibanez Radius series has a very distinct body form. The contoured body shape is beveled around the outside edge also called the aerofoil edge, which pulls the body closer to the player for comfort in playing.
The series were made in Japan from 1987 until 1993.
The first generation of Radius guitars featured basswood bodies, Ultra necks, Ibanez edge tremolo's, tilt neck joints and IBZ USA pickups that were codesigned with DiMarzio. There were HSS, HSH and HH models. Later on there were models featuring alder bodies, Ibanez Lo Pro edge tremolo's, Ibanez TZ tremolo's, All Access Neck Joints, Wizard necks, Viper necks and Ibanez pickups.
The Ibanez Radius series would be the base of the Ibanez Joe Satriani series that came after the Radius series.
