A designation covering machines that were designed after 1970 (approximately).

Conceptually the most important criterion that can be used to separate them from the third generation is that they were designed to work efficiently with the current generation of high-level languages—fourth-generation languages—and were intended to be easier to program by their end-user. From a hardware point of view they are characterized by being constructed largely from integrated circuits and have multi-megabyte fast RAM fabricated in MOS technology. These volatile memories are intimately connected to high-speed disk units so that on power failure or switch-off, data in MOS memory is retained by automatic transfer to the disks. On switch-on, commonly the system is started up from a bootstrap ROM, which loads the operating system and resident software back into the MOS memory as required.