Hand beaded computer RAM
I love revisiting ancient technology. Especially when it's as much a work of art as a piece of tech. Magnetic core memory absolutely fits with this description. Here we have a tapestry woven in copper wires, strung through small circular beads of ferrite, or 'cores.' Each tiny iron based donut represents one bit of digital memory. This exotic blend of electrical engineering and macrome was a mainstay of computers built by the ancients during the 1950s-1980s.
The chief advantages of core memory over other forms of digital memory at the time was that it was true random-access, and was super-fast. You could get bits into and out of it in mere nanoseconds, vs the milliseconds required with tape or spinning disk or acoustic memories. Also, it was non-volatile, meaning it held its data even without having power connected.
Disadvantages (like everything of the early age of computing) included it being hand-made, complex, expensive, and relatively large. Here is a memory block containing 30Kb. It's the size of a microwave oven:
Today, integrated circuit technology has totally replaced all applications of magnetic core memory. The most notable non-volitile memories that replaced it are EEPROM and FLASH technologies. These are small, fast, and comparatively very cheep. FLASH has also begun to take on the roll as a mass storage media, replacing hard disks etc. The more volatile static and dynamic RAM that live in your computer essentially fill the roll of core memory as it was used for the active program memory.
Interestingly enough, core memory, is still more mechanically robust and is entirely insensitive to static electric shock. (All of our current IC technologies cope poorly with the latter!) NASA understood these die-hard qualities when it put magnetic core memory in the space shuttles' on board computers well into the late 1980s. The space shuttle Challenger had magnetic core memory in its navigational computer systems, which was recovered and found to be readable after disaster sent it to the bottom of the sea.
The basic concepts of core memory have evolved into new families of memory systems. There was something called 'magnetic bubble memory' that was being developed in the late 1990s, but became outmoded by smaller hard disks and flash memory. An on-chip memory system dubbed 'racetrack memory' uses similar magnetic properties to hold large quantities of data on an integrated circuit. In theory, it could offer speeds and densities higher than that of FLASH memory.
The state of the art non-volatile memory systems are based not on magnetic properties but on various material junctions that change resistance with current flow over time in a given direction. They show promise, but perhaps less romance than the magnetic memories of old.
Physicist Richard Feynman famously said, "What I cannot create, I do not understand." It's fun and mid-bending to imagine actually building computers bit by magnetic bit. If you're interested in learning more about magnetic core memory, there are actually some great DIY projects online. Go ahead, make some great memories!
An awesome report on a hand-built magnetic core project by Ben North & Oliver Nash: http://www.corememoryshield.com/report.html
Some cool stuff on HackADay: Core Memory for the Hard Core by Elliot Williams: