Drum memory, an early form of computer memory, used the drum as a working part, with data loaded to the drum. The drum was a metal cylinder coated with a recordable ferromagnetic material. The drum also had a row of read-write heads that wrote and then read the recorded data.

Magnetic core memory (ferrite-core memory) is another early form of computer memory. Magnetic ceramic rings called cores, stored information using the polarity of a magnetic field.

Semiconductor memory is computer memory we are all familiar with, computer memory on an integrated circuit or chip. Referred to as random-access memory or RAM, it allowed data to be accessed randomly, not just in the sequence it was recorded.

Dynamic random access memory (DRAM) is the most common kind of random access memory (RAM) for personal computers. The data the DRAM chip holds have to be periodically refreshed. Static random access memory or SRAM doesn't need to be refreshed.

Timeline of Computer Memory

1834 - Charles Babbage begins to build his "Analytical Engine", a precursor to the computer. It uses read-only memory in the form of punch cards.

1932 - Gustav Tauschek invents drum memory in Austria.

1936 - Konrad Zuse applies for a patent for his mechanical memory to be used on his computer. This computer memory is based on sliding metal parts.

1939 - Helmut Schreyer invents a prototype memory using neon lamps.

1942 - The Atanasoff-Berry Computer has 60 50-bit words of memory in the form of capacitors mounted on two revolving drums. For secondary memory, it uses punch cards.

1947 - Frederick Viehe of Los Angeles applies for a patent for an invention that uses magnetic core memory. Magnetic drum memory is independently invented by several people:

An Wang invented the magnetic pulse controlling device, the principle upon which magnetic core memory is based.

Kenneth Olsen invented vital computer components, best known for "Magnetic Core Memory" Patent No. 3,161,861 and as being the co-founder of Digital Equipment Corporation.

Jay Forrester was a pioneer in early digital computer development and invented random-access, coincident-current magnetic storage.

1949 - Jay Forrester conceives the idea of magnetic core memory as it is to become commonly used, with a grid of wires used to address the cores. The first practical form manifests in 1952-53 and renders obsolete previous types of computer memory.

1950 - Ferranti Ltd. completes the first commercial computer with 256 40-bit words of main memory and 16K words of drum memory. Only eight were sold.

1951 - Jay Forrester files a patent for matrix core memory.

1952 - The EDVAC computer is completed with 1024 44-bit words of ultrasonic memory. A core memory module is added to the ENIAC computer.

1955 - An Wang was issued U.S. patent #2,708,722 with 34 claims for magnetic memory core.

1966 - Hewlett-Packard releases their HP2116A real-time computer with 8K of memory. The newly formed Intel starts to sell a semiconductor chip with 2,000 bits of memory.

1968 - USPTO grants patent 3,387,286 to IBM's Robert Dennard for a one-transistor DRAM cell. DRAM stands for Dynamic RAM (Random Access Memory) or Dynamic Random Access Memory. DRAM will become the standard memory chip for personal computers replacing magnetic core memory.

1969 - Intel begins as chip designers and produces a 1 KB RAM chip, the largest memory chip to date. Intel soon switches to being notable designers of computer microprocessors.

1970 - Intel releases the 1103 chip, the first generally available DRAM memory chip.

1971 - Intel releases the 1101 chip, a 256-bit programmable memory, and the 1701 chip, a 256-byte erasable read-only memory (EROM).

1974 - Intel receives a U.S. patent for a "memory system for a multichip digital computer".

1975 - Personal consumer computer Altair released, it uses Intel's 8-bit 8080 processor and includes 1 KB of memory. Later in the same year, Bob Marsh manufacturers the first Processor Technology's 4 kB memory boards for the Altair.

1984 - Apple Computers releases the Macintosh personal computer. It is the first computer that came with 128KB of memory. The 1 MB memory chip is developed.