The 555 is part of the SP family, which includes Boss’s popular SP-303 and Roland's SP-404 installments.
The following list is a correct order of each SP installment's release, as an attempt to help musicians avoid any confusion.
A total of 37 built-in effects can be assigned to 16 pressure-sensitive pads.
In similarity to the SP-808 installment, the sampler has the D Beam feature, which allows one to control 3 different effects physically, including synth, trigger, and filter.
The SP-555 also has several pre-loaded live FX, including Voice Transformer, Delay, Isolator, "Super Filter", and "DJFX Looper".