Writeable variants of ROM (such as EEPROM and flash memory) share properties of both ROM and RAM, enabling data to persist without power and to be updated without requiring special equipment.
Nevertheless, a DVD-RAM behaves much like a hard disc drive if somewhat slower.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.ECC memory (which can be either SRAM or DRAM) includes special circuitry to detect and/or correct random faults (memory errors) in the stored data, using parity bits or error correction codes.In general, the term RAM refers solely to solid-state memory devices (either DRAM or SRAM), and more specifically the main memory in most computers.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.
The capacitor holds a high or low charge (1 or 0, respectively), and the transistor acts as a switch that lets the control circuitry on the chip read the capacitor's state of charge or change it.
As this form of memory is less expensive to produce than static RAM, it is the predominant form of computer memory used in modern computers.
Integrated-circuit RAM chips came into the market in the early 1970s, with the first commercially available DRAM chip, the Intel 1103, introduced in October 1970. Ultrasonic delay lines could only reproduce data in the order it was written.
Drum memory could be expanded at relatively low cost but efficient retrieval of memory items required knowledge of the physical layout of the drum to optimize speed.
In modern computers, SRAM is often used as cache memory for the CPU.