Thanks for the memories - Embedded.com

Thanks for the memories

If each of our hands had eight fingers, we'd count in hexadecimal and non-geeks wouldn't puzzle over numbers that include the letters A through F. But would we still start at one instead of zero?

How often have you seen a child learning to enumerate hold three fingers out in an effort to remember how many of something he just counted? Perhaps these digits were the earliest memory devices.

Or maybe not. Long before writing was invented people had developed storytelling to a fine art. Oral traditions taught the young to avoid the bad berries and saber-toothed tigers. Long before being committed to paper or papyrus, the Bible was transmitted between generations by word of mouth. Matthew and Luke's begats most likely mirrored how elders tracked their own family history.

The very concept of “mine” that toddlers unceasingly chant likely is buried deep in our genes. Unless earliest societies were truly communal, Grog the caveman would have needed some sort of device, perhaps piles of stones, to track exactly how much was “mine.”

At some point humans made the leap from physical representations of quantities to the abstract. Perhaps the first form of writing involved scratching lines in the dirt as a memory aid. I have read that the earliest symbols existed as far back as some 30,000 years ago. These were mnemonics rather than novels; but the very word mnemonic means “memory aid.” Clearly, humankind has long wanted mass storage. Unfortunately, the early history of writing has gone to /dev/null .

Some scholars date the Tărtăria tablets from Romania back to 5,500 BC, in which case they may preserve the oldest known written data. The regular shapes of the glyphs encoded in the clay suggest that standardized writing had existed for some time. No one knows what the symbols mean, but a media that lasts seven thousand years puts all of our modern high-tech solutions to shame.

Just as the Kindle uses sequences of ones and zeroes to store the Kama Sutra , at some point most societies moved from pictographs to alphabets. Egyptian hieroglyphs contain elements of both. Our alphabet reduces the number of symbols needed to express complex ideas from thousands to 26. Fewer symbols means more storage is needed to encode an idea, but there's no practical limit to the things that can be described. This remains a very diverse world, so ironically we still need thousands of representations in Unicode to build computers useful to the planet's population.

Clay tablets gave way to papyrus and parchment. The latter, made from animal skin, is quite expensive and led to what was perhaps the first rewritable storage medium: the palimpsest. Scribes would scrape or wash the ink from a parchment document and write again on the now-blank sheet. In fact here in Baltimore, the Walters Art Museum holds the Archimedes Palimpsest(www.archimedespalimpsest.org/). In the tenth century an unknown scribe copied some of Archimedes' work onto parchment; two centuries later it was reused for a liturgical text. Science has been able to reveal the original text, which is fortunate as it has the only known copy of the sage of Syracuse's The Method of Mechanical Theorems .

I suppose one could make the argument that the abacus was a storage device, since, like the registers in a CPU, it held numbers during a calculation. The Sumerians had this technology, in a primitive form, nearly 5,000 years ago. The Romans called the limestone pebbles used in their table abacuses “calculi,” from which we derive the word “calculate.”

After the invention of paper in China around the second century, not much happened to storage technology for thousands of years. Paper remained expensive and was hand-made until the 19th century, and indeed history records “rag pickers” who recycled old cloth for papermaking.

Most techies know that the punched card long predated mainframes. Cards and paper tape were originally adopted in France in the early 18th century to control textile looms. (I would have thought that the idea of punching holes in paper to store instructions and data stemmed from player pianos, but those didn't come around till over a century later.)

Charles Babbage designed a calculating machine that used punched cards, but he wasn't the one to couple cards to computing. Russian Semen Korsakov, a bureaucrat in a police statistics department, anticipated Google when he invented several machines that used punched cards to search though data. But they remained a novelty in information processing until Herman Hollerith built machines to record data for the 1890 census. His company later morphed into IBM. That company supported a number of different kinds of punched cards, but their 80-column version remains the iconic image of the technology.

My grandmother died years ago at age 99, still furious at FDR (she couldn't even say his name, always blurting out “that man!”) for creating Social Security and other Depression-era programs. She drew on Social Security for 34 years. But FDR's creation did drive a massive expansion in the use of punched card machines, and so in some way contributed to the birth of the computer industry. (Aside: Ida May Fuller got the first SS check. She paid $24.75 into the system, or one percent of three year's income, and netted almost $23,000 in payouts before dying at age 100, surely one of the great jackpots of all time!)

Computer centers used fantastic quantities of punched cards. In the early 1970s, the University of Maryland supplied unlimited quantities to students for free. A 10,000-line program needed 10,000 cards, which filled five boxes. Even as early as 1937, IBM manufactured five to 10 million cards a day. Yet when working on the ESC's twentieth anniversary event, I could find none, except from a vendor who charged a buck a card, since they faded away in the '70s as other media became more cost effective.

Paper tape, too, was initially used for looms. Both Morse and Edison worked on paper tape systems for telegraphy, though their systems initially used marks made on the tape instead of holes. In the 1920s, various communications links using teletypewriters were established. The infamous newsrooms of yore with dozens of these clanking machines are an example. Prior to and during World War II, the Teletype corporation built some 200,000 of their model 15 teletypewriters (often called “teletypes,” just as copiers are referred to as “xerox machines.”) These usually had a paper tape reader and punch attached with which to log and send streams of messages. All of the model 15 machines I have seen use a five-level code derived from Baudot rather that the ASCII 8 or Unicode's zillions common today. Mechanical fingers probed the holes across the tape and converted the pattern to a 5-bit parallel stream, which was sent to what looked exactly like a car's distributor (for a five cylinder car, that is). Five contacts were swept by a rotor to convert the parallel to serial.

Konrad Zuse in Germany used paper tape to feed instructions to his Z1 machine, completed in 1938. He also used moving metal sheets as main memory, for a total of sixty-four 22-bit words (www.epemag.com/zuse/part3b.htm).

Teletype's ASR-33 appeared in 1961. At $2,000 (about $14,000 today), it was inexpensive, as these machines went, and was a perfect match for the newly emerging minicomputers.

The machine had a built-in 8-bit paper tape reader and punch that read tape at a blistering 10 characters per second. It's interesting that the incredibly complex mechanical mechanism of the ASR-33 was much cheaper than the electronics needed to build a video terminal, so these machines were common in computer centers. The racket 50 of them made in a terminal room cannot be imagined. ASR-33s were the first terminals used by microprocessor development systems.

The story of computers is one of speed, and 10 CPS didn't tax even the low-powered machines of the '60s. High-speed paper-tape readers appeared, which could suck tape through at hundreds of characters per second. When something went wrong, these devices would spew a snarl of tape that could fill an office in seconds.

Vendors of both mini- and micro-computers delivered their tools on tape. Happily, programs then were not 500-MB monsters!

Tape remained the mass storage of choice in the '70s till supplanted by magnetic media.

Meanwhile, other forms of memory were tried, used and abandoned. A complete list would take volumes, but here are some of my favorites.

Today, we store programs and data in, among other things, active elements like transistors. That's not a new concept. The vacuum tube is an active element as well, and was used in early computers both as ALU and memory. Of course, a tube is about the size of a skyscraper compared to 45-nm FETs, and dissipates enormous amounts of heat. ENIAC stored twenty 10-digit numbers in ring counters. Every digit stored needed 36 tubes.

Core memory came about either from a paper by An Wang, whom old-timers recognize as the man behind once-great Wang Laboratories, or from Jay Forrester and Ken Olsen in their work on the Whirlwind computer, depending on which sources one believes. Wang's paper came out in 1949, but core didn't become viable in computers till the following decade. Core memory is composed of large planes of tiny ferrite donuts. Three or four wires are threaded through each torus, and they are all interconnected in an X-Y matrix. By sending small currents through a row and a column it's possible to flip the magnetic field of the core located at the X-Y intersection. A sense wire detects the transition to signal if the core was set to a zero or one. This is a destructive read, so another cycle resets the core. Compared with other early memory devices, core was very fast, switching in under a microsecond.

Core became the standard memory store for all computers from the '50s until superseded by semiconductor memory in the '70s. Though early cores weren't much smaller than a Cheerio, eventually sizes shrank tremendously. Prices did too, falling to about a penny a bit, about seven orders of magnitude more than what memory costs today. Think about that–what other industry has seen costs tumble so precipitously?

The Whirlwind machine mentioned in the previous paragraph eventually had core memory, but initially relied on Williams-Kilburn tubes. These were essentially CRTs that painted bits on the phosphor screen (some versions didn't bother with the phosphor coating). A metal plate on the front of the screen sensed the charges. Typical Williams-Kilburn tubes could hold a few hundred to a thousand bits; those used in the Whirlwind stored 256 bits each. Unfortunately, the tubes aged poorly, couldn't be scaled up to higher memory densities, and were very subject to electronic noise.

But they were a pretty cool idea.

And I've run out of room. More next month!

Jack Ganssle () is a lecturer and consultant specializing in embedded systems' development issues. For more information about Jack .

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