There are two different forms of RAM, static RAM (SDRAM) and dynamic RAM (DRAM). Static ram is more expensive to produce than dynamic ram, but it’s generally faster and requires less power than DRAM. In computers, it’s often used as cache memory for the CPU Processor.
Dynamic ram (DRAM) stores the bits of data by using a transistor and a capacitor, together the transistor and capacitor creates a memory cell. The capacitor holds a high or low charge (1 or 0,), and the transistor acts as a switch that controls the circuitry on the chip that reads the capacitor's state of charge or changes it. As this form of memory is less expensive to produce than static ram, it is the main form of computer memory used in most computers today.
The static and dynamic ram are both considered as volatile, as their state is lost or reset when power is removed from the system which causes the data that’s stored to be lost when the computer is shut off.
Read-only memory (ROM) stores data permanently by enabling or disabling selected transistors, this way the memory cannot be altered. There are some variants of ROM (such as EEPROM and flash memory) that share properties of both ROM and RAM. These variants enable data to be saved and stored without power and to be updated without requiring any special equipment. These forms of semiconductor ROM include USB flash drives, memory cards for cameras and portable devices, etc. As of 2007, flash devices have begun to replace older forms of persistent storage, such as magnetic disk hard drives and tape drives. While flash is being used in place of ROM in netbooks and computers, since it is capable of true random access, allowing direct code execution. This is why you see the solid state hard drives as a replacement for magnetic disks because of its extreme performance.
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 code. These types of ram are common in server machines that need the high reliability and uptime. This type of ram is also much more expensive and a bit slower in performance than traditional types of ram that are found in computers such as desktops and laptops.
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.