First recognized in 60'an. Only when the semiconductor memory that has not been popular because the price is very expensive. When it is more common to use magnetic main memory.
Semiconductor companies such as Intel started producing his debut with RAM, more precisely, DRAM types.
Usually RAM can be written and read, as opposed to read-only memory (read-only-memory, ROM), RAM is usually used for primary storage (main memory) for use in computers and change the information actively, although some tools use some kind of RAM to provide long-term secondary storage.
But there is also an opinion that the ROM is another type of RAM, because it is really too random access such as SRAM or DRAM. It's just that indeed the process of writing the ROM does not require a specific process as easy and flexible as well as in the SRAM or DRAM. Also addresses some part of the space of RAM (main memory) of a system that is mapped into one or two chip ROM.