Taking A Walk Down [Computer] Memory Lane

August 9, 2021 by Ryan Flowers 15 Comments

There’s nothing quite like going to a museum and being given a tour by a docent who really knows their way around the exhibits. When that docent has first hand experience in the subject matter, the experience is enhanced even further. So you can imagine our excitement when hacker, maker, and former DEC mainframe memory engineer [Ned Utzig] published a tour of what he calls “Memories of Weird Memories of Computers Past.” [Ned] expertly guides us through each technology, adding flavor and nuance to an already fascinating subject.

The tour begins with early storage media such as IBM punch cards, and then walks us through time to the paper tape, vacuum tubes, and even complex vats of mercury — all used for the sake of storing data either permanently or temporarily.

Next in the exhibit is an impressive CRT hack that isn’t unlike modern DRAM. The tour continues on to ferrite core memory such as that used on mainframes, minicomputers, and even the Apollo Guidance Computer. Each type is examined for its strengths and weaknesses and its place in computing history.

We really appreciated the imaginative question posed toward the end of the article. We won’t give it away here- it’s worth it to go give The Mad Ned Memo a read.

Is obsolete technology your cup of tea? Perhaps an Arduino based experiment with core memory will scratch the itch, or maybe storing data in thin air will bring back memories of computers gone by.

Thanks For The Memories: Touring The Awesome Random Access Of Old

March 8, 2016 by Al Williams 41 Comments

I was buying a new laptop the other day and had to make a choice between 4GB of memory and 8. I can remember how big a deal it was when a TRS-80 went from 4K (that’s .000004 GB, if you are counting) to 48K. Today just about all RAM (at least in PCs) is dynamic–it relies on tiny capacitors to hold a charge. The downside to that is that the RAM is unavailable sometimes while the capacitors get refreshed. The upside is you can inexpensively pack lots of bits into a small area. All of the common memory you plug into a PC motherboard–DDR, DDR2, SDRAM, RDRAM, and so on–are types of dynamic memory.

The other kind of common RAM you see is static. This is more or less an array of flip flops. They don’t require refreshing, but a static RAM cell is much larger than an equivalent bit of dynamic memory, so static memory is much less dense than dynamic. Static RAM lives in your PC, too, as cache memory where speed is important.

For now, at least, these two types of RAM technology dominate the market for fast random access read/write memory. Sure, there are a few new technologies that could gain wider usage. There’s also things like flash memory that are useful, but can’t displace regular RAM because of speed, durability, or complex write cycles. However, computers didn’t always use static and dynamic RAM. In fact, they are relatively newcomers to the scene. What did early computers use for fast read/write storage?

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Storing 32 Bits Of Data In A Piece Of Glass

November 9, 2012 by Brian Benchoff 35 Comments

After finding an old piezoelectric delay line in an old TV, [Mike] decided to figure out how it works and in the process stored his name in sound waves reflecting inside a piece of glass

[Mike] was intrigued by these old-fashioned delay lines after watching [Dave] from EEVblog’s teardown of an circa 1985 camcorder. [Dave] found a piezoelectric delay line in his camcorder – a device that is able to store digital data by sending a sound wave into a glass plate, letting the sound wave bounce through the plate. and picking up the sound on the other end. It’s actually not too dissimilar to a mercury delay line used in the earliest computers.

After sending a pulse through his piezoelectric delay line, [Mike] picked up an echo almost exactly 64 microseconds later. After hooking up a simple circuit constructed out of a 74-series chip, [Mike] found he could ‘loop’ the delay line and keep a pulse going for up to 3 milliseconds.

Three milliseconds isn’t much, but by injecting serial data into the delay line, [Mike] was able to spell out his name in binary, as seen above. It’s just 32 bits stored for a fraction of a second, making it a very volatile, low-capacity memory, but functionally equivalent to the old mercury delay lines of yore.

It’s certainly not what [Mike] or [Dave]’s delay line was designed to do; these video delay lines were used to hold the previous line of video for a form of error correction. Outside [Mike]’s workbench and a few museums, though, you won’t see a delay line used as a form of computer memory. A very cool build and an awesome history lesson, and we thank [Mike] for that.