PDP-4
 | |
 The PDP-4 on display at NARA's auditorium stage in Washington, D.C., 1964 | |
| Developer | Digital Equipment Corporation |
|---|---|
Product family | Programmed Data Processor |
| Type | Minicomputer |
| Released | 1962 |
Introductory price | US$65,000 (equivalent to $691,832 in 2025) |
| Units sold | Approximately 54 |
| Media | Paper tape |
| Platform | PDP 18-bit |
| Weight | 1,090 pounds (490 kg) |
| Predecessor | PDP-1 |
| Successor | PDP-7 |
The PDP-4 is an 18-bit computer system that was introducted in 1962 as a successor to the Digital Equipment Corporation's PDP-1. However, this was a completely new system, incompatible with the PDP-1. For example, the PDP-1 used ones' complement arithmetic whereas the PDP-4 used two's complement, a much faster way to implement multiple precision and floating-point operations.