Short answers, pulled from the story.
The Manchester Baby computer successfully ran its first program in June of 1948 using a Williams tube for main memory. This machine stored data as electrically charged spots on the face of a cathode-ray tube that an electron beam could read and write in any order.
Magnetic-core memory appeared in 1947 and dominated until the mid-1970s when semiconductor memory displaced it. Engineers constructed arrays of magnetized rings to store data where each ring represented a single bit through its direction of magnetization.
Robert Dennard invented modern DRAM architecture in 1966 with a single transistor per capacitor. Intel released the first commercial DRAM IC chip known as the 1103 in October 1970 which held one kilobit of data on an eight-micrometer process.
Static RAM uses six transistors to store each bit while Dynamic RAM relies on a single transistor paired with a capacitor. Static RAM serves as cache memory for CPUs due to its speed whereas Dynamic RAM dominates main memory systems because it is cheaper to produce.
The first commercial double data rate SDRAM arrived in June 1998 from Samsung and held sixty-four megabits of data. Graphics DDR emerged as a form of synchronous graphics RAM also released by Samsung in 1998 utilizing sixteen megabits initially before scaling up.