Other types of non-volatile memories exist that allow random access for read operations, but either do not allow write operations or have other kinds of limitations on them.These include most types of ROM and a type of flash memory called NOR-Flash.In optical storage, the term DVD-RAM is somewhat of a misnomer since, unlike CD-RW or DVD-RW it does not need to be erased before reuse.Nevertheless, a DVD-RAM behaves much like a hard disc drive if somewhat slower.
By changing the sense of each ring's magnetization, data could be stored with one bit stored per ring.
Both static and dynamic RAM are considered volatile, as their state is lost or reset when power is removed from the system.
By contrast, read-only memory (ROM) stores data by permanently enabling or disabling selected transistors, such that the memory cannot be altered.
Developed at the University of Manchester in England, the Williams tube provided the medium on which the first electronically stored-memory program was implemented in the Manchester Small-Scale Experimental Machine (SSEM) computer, which first successfully ran a program on 21 June 1948.
Magnetic-core memory was invented in 1947 and developed up until the mid-1970s.