An EPROM, or erasable programmable read-only memory, is a type of programmable read-only memory chip that retains its data when its power supply is switched off. Computer memory that can retrieve stored data after a power supply has been turned off and back on is called non-volatile, it is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages than those used in digital circuits. Once programmed, an EPROM can be erased by exposing it to strong ultraviolet light source. EPROMs are recognizable by the transparent fused quartz window in the top of the package, through which the silicon chip is visible, which permits exposure to ultraviolet light during erasing. Development of the EPROM memory cell started with investigation of faulty integrated circuits where the gate connections of transistors had broken. Stored charge on these isolated gates changes their threshold voltage. Following the invention of the MOSFET by Mohamed Atalla and Dawon Kahng at Bell Labs, presented in 1960, Frank Wanlass studied MOSFET structures in the early 1960s.
In 1963, he noted the movement of charge through oxide onto a gate. While he did not pursue it, this idea would become the basis for EPROM technology. In 1967, Dawon Kahng and Simon Sze at Bell Labs proposed that the floating gate of a MOSFET could be used for the cell of a reprogrammable ROM. Building on this concept, Dov Frohman of Intel invented EPROM in 1971, was awarded U. S. Patent 3,660,819 in 1972. Frohman designed the Intel 1702, a 2048-bit EPROM, announced by Intel in 1971; each storage location of an EPROM consists of a single field-effect transistor. Each field-effect transistor consists of a channel in the semiconductor body of the device. Source and drain contacts are made to regions at the end of the channel. An insulating layer of oxide is grown over the channel a conductive gate electrode is deposited, a further thick layer of oxide is deposited over the gate electrode; the floating-gate electrode has no connections to other parts of the integrated circuit and is insulated by the surrounding layers of oxide.
A control gate electrode is deposited and further oxide covers it. To retrieve data from the EPROM, the address represented by the values at the address pins of the EPROM is decoded and used to connect one word of storage to the output buffer amplifiers; each bit of the word is a 1 or 0, depending on the storage transistor being switched on or off, conducting or non-conducting. The switching state of the field-effect transistor is controlled by the voltage on the control gate of the transistor. Presence of a voltage on this gate creates a conductive channel in the transistor. In effect, the stored charge on the floating gate allows the threshold voltage of the transistor to be programmed. Storing data in the memory requires selecting a given address and applying a higher voltage to the transistors; this creates an avalanche discharge of electrons, which have enough energy to pass through the insulating oxide layer and accumulate on the gate electrode. When the high voltage is removed, the electrons are trapped on the electrode.
Because of the high insulation value of the silicon oxide surrounding the gate, the stored charge cannot leak away and the data can be retained for decades. The programming process is not electrically reversible. To erase the data stored in the array of transistors, ultraviolet light is directed onto the die. Photons of the UV light cause ionization within the silicon oxide, which allow the stored charge on the floating gate to dissipate. Since the whole memory array is exposed, all the memory is erased at the same time; the process takes several minutes for UV lamps of convenient sizes. The EPROMs must be removed from equipment to be erased, since it is not practical to build in a UV lamp to erase parts in-circuit; the Electrically Erasable Programmable Read-Only Memory was developed to provide an electrical erase function and has now displaced ultraviolet-erased parts. As the quartz window is expensive to make, OTP chips were introduced. OTP versions of both EPROMs and EPROM-based microcontrollers are manufactured.
However, OTP EPROM is being replaced by EEPROM for small sizes, where the cell cost isn't too important, flash for larger sizes. A programmed EPROM retains its data for a minimum of ten to twenty years, with many still retaining data after 35 or more years, can be read an unlimited number of times without affecting the lifetime; the erasing window must be kept covered with an opaque label to prevent accidental erasure by the UV found in sunlight or camera flashes. Old PC BIOS chips were EPROMs, the erasing window was covered with an adhesive label containing the BIOS publisher's name, the BIOS revision, a copyright notice; this label was foil-backed to ensure its opacity to UV. Erasure of the EPROM begins to occur with wavelengths shorter than 400 nm. Exposure time for sunlight of one week or three years for room fluorescent lighting may cause erasure; the recommended erasure procedure is exposure to UV light at 253.7 nm of at least 15 Ws/cm2 achieved in 20 to 30 minutes with the lamp at a distance of about 2.5 cm.
Erasure can be accomplished with X-rays: Erasure, howe
An iceman is someone who sells or delivers ice from a wagon, cart, or motor-truck. The profession was much more common than it is today. From the late 19th century to mid-20th century, in cities and towns icemen would make daily rounds delivering ice for iceboxes before the electric domestic refrigerator became commonplace. Many icemen in the Northeastern U. S. had origins in Southern Italy. Arriving in the U. S. with little education or trade skills, many of these immigrants began ice routes in New York City, where ice routes were a common sight. In those times, ice was harvested from ponds and lakes, stored in ice houses and transported to cities. Modern day icemen no longer use a wagon or cart to deliver their ice, but instead use freezer trucks which contain pallets stacked with bags of ice cubes and large blocks of ice. Many of the old-fashioned small-time routes were bought out in the 1980s and 1990s by large ice corporations that sell and produce ice, as well as ice machines, to restaurants and bars.
The tools of the iceman were wires, hooks and ice picks. Being an iceman was arduous. Icemen began their day at 4:00 am and finished late in the evening, depending on both the season and day of the week. Many icemen through holidays; as Arthur Miller recalls in his autobiography Timebends, "icemen had leather vests and a wet piece of sackcloth slung over the right shoulder, once they had slid the ice into the box, they invariably slipped the sacking off and stood there waiting, for their money."The occupation of ice delivery lives on through Amish communities, where ice is delivered by truck and used to cool food and other perishables. A reference to the past history of the iceman occupation can be seen in Disney's animated films Frozen and Frozen II, where the character Kristoff learns the trade from a young age. Ice trade Ice cutting Ice boxing ^ Arthur Miller, Timebends: A Life, 64. Media related to Icemen at Wikimedia Commons Icebox Memories A Nairobi-based ice delivery company Joseph C. Jones, J.
R.: America's Icemen: An Illustrative History of the United States Natural Ice Industry 1665-1925. Humble, TX: Jobeco Books 1984
The men's marathon at the 2015 World Championships in Athletics was held at the Beijing National Stadium on 22 August. The name Gebrselassie is familiar in running circles, but this race was won by Haile's sound alike Ghirmay Ghebreslassie from a different country, neighboring Eritrea. Not only was he the youngest winner of a World Championship marathon, he was the first gold medalist for his country ever; the early leader was Ser-Od Bat-Ochir Daniele Meucci and Ruggero Pertile getting camera time to the half way mark while the favorites including defending champion Stephen Kiprotich stayed off the pace. Ghebreslassie marked the more experienced runners. Tsepo Ramonene made a breakaway at 25 km opening up a 30-second lead; as he watched two Kenyans drop out and other favorites struggle, Ghebreslassie decided to set loose at 34 km. Over the next couple of kilometers, he passed Ramonene with authority, but a couple of kilometers Yemane Tsegay passed Ghebreslassie. Tsegay's lead only lasted two minutes.
Over the final kilometers, he extended his lead to 40 seconds. Running relaxed and fast like an exuberant teenager, he was handed an Eritrean flag as he entered the stadium, he held his flag but kept on running past the finish line until officials were able to tell him he was done. “I’ve never finished in a stadium before.” Behind him, in comparison, Solomon Mutai and the other runners finished looking as if they had just finished a marathon. Prior to the competition, the records were as follows: All times are local times The race was started at 07:35