Lunar Calendar (c. 15,000 B.C.E.)

Early humans record the passing of time.

The earliest known lunar calendar is in the caves at Lascaux, southwest France, and dates from around 15,000 B.C.E. Various series of spots represent half of the moon's near-monthly cycle, followed by a large empty square, which perhaps indicated a clear sky.

   A  lunar calendar counts months ( a period of 29.530588 days) and is based on the phrases of the moon. Months have twenty-nine and thirty days alternately, and additional days are added every now and then to keep step with the actual moon phase.

   The lunar calendar was widely used in parts of the ancient world for religious observation. Agriculturally the lunar calendar is confusing as it takes no account of annual seasonal variations in temperature, daylight lenght, plant growth, animal migration, and mating. .the lunar month divides into the solar year twelve times but with 10.88 days remaining.

  Meton of Athens (circa 440 B.C.E.) noticed that nineteen-year Metonic cycle where years three, five, eight, thirteen, sixteen, and nineteen had thirteen lunar months each, and all the other years had twelve months.

"DAY ARE PUSHED BY THE DAY, AND EACH NEW MOON HASTENS TO ITS DEATH.."

                                                                                                                      -Horace, Odes, Book II

Random Access Memory (RAM) (1968)

Dennard combines a transistor with a capacitor in a revolutionary memory cell.

   
RAM, or Random Access Memory, the short term, high speed "working" memory of a computer, has existed sine the invention of magnetic core memory in 1949. Modern RAM, though, owes its invention to Texan Robert Dennard (b. 1932).

     In 1966 Dennard was working at IBM's Thomas J. Watson Research Center. IBM knew that magnetic core memory was too bulky, power-hungry, and slow, and that transistors would be the answer to replacing it. They had reduced the problem of storing a single bit of memory to a cell that used only six transistors. Added to a silicon chip, this cell was already tiny compared to a magnetic core. Dennard, though, simplified the memory cell even more, to a single transistor and capacitor, a component that an hold an electric charge. The memory was stored as charge on the capacitor, and the transistor was used to read and write it. Capacitors "leak" charge, though, so the memory had to be continuously refreshed, many times a second. Because of this constant forgetting and refreshing, Dennard's system is called "dynamic" RAM, or DRAM.

    Despite its need to be refreshed, DRAM had a world-beating advantage. With only two components, which could be placed side by side in the thousands on a single silicon chip, it was the smallest memory ever made. The computer industry quickly took advantage of Dennard's invention, and fledgling company Intel released the first commercial DRAM chip in 1970. Magnetic core memory became the technology of yesteryear almost as soon as Intel began to ship its new chip.