The PDP-11 is a series of 16-bit minicomputers sold by Digital Equipment Corporation (DEC) from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 had several uniquely innovative features, and was easier to program than its predecessors through the additional general-purpose registers. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years. In total, around 600,000 PDP-11s of all models were sold, making it one of DEC's most successful product lines. Its successor in the mid-range minicomputer niche was the 32-bit VAX-11, named as a nod to the PDP-11's popularity.