RAM is usually used to store information of running programs inside computers. RAM may also be used for different things.
Using virtual memory, a computer can combine permanent storage with RAM to create a bigger pool of storage. This is useful when the RAM does not have enough space to store anymore information. The extra data is then placed in the permanent storage instead of the RAM. The method has a limitation which is that permanent storage is often slower than RAM, which can slow down a computer.
A computer can use a part of the RAM to store permanent files. This is called a RAM disk. When the computer is turned on, files are copied to the RAM disk. This allows the files to open faster because RAM is faster than permanent storage. When the computer is turned off, the information on the RAM disk is lost, which is why the files need to exist on permanent storage as well.
Information that the computer always needs, that cannot be changed or deleted (unless it is EEPROM), is normally kept in read-only memory (ROM), which does not lose its contents when the computer is turned off. Such items include the BIOS (Basic Input/Output System), which stores the most basic commands for the computer, telling it how it should start up. The BIOS also tells the computer how to input and output information. The BIOS can be compared to the part of your brain that tells your heart how to beat. This is an important part.
Read-only memory
Read-only memory (or simply ROM) is a type of computer memory. Unlike RAM, it keeps its contents even when the computer or device is turned off. Usually, ROM cannot be written to when the computer runs normally. ROM is used for the BIOS which tells the computer how to start, or important programs like the firmware of certain devices, which usually does not need to be modified. Usually, ROM comes on computer chips.
There are different kinds of ROMs:
Integrated circuit
An integrated circuit (more often called an IC, microchip, silicon chip, computer chip, or chip) is a piece of specially prepared silicon (or another semiconductor) into which an electronic circuit is etched using photolithography. Silicon chips can contain logic gates, computer processors, memory and special devices. The chip is very fragile and so is normally surrounded by a plastic package to protect it. Electrical contact with the chip is provided through tiny wires that connect the chip to larger metal pins that stick out of the package.
An IC has two main advantages over discrete circuits: cost and performance. Cost is low, because millions of transistors can be put onto one chip instead of building a circuit with single transistors. Performance is higher since the components can operate more quickly and use less power.
ICs are designed for different purposes. A chip may be designed just for a calculator, which can only work as a calculator. Integrated circuits can be classified into analog, digital and mixed signal (both analog and digital on the same chip).
A semiconductor such as silicon can be controlled to allow (or not allow) current to flow. This allows making transistors that can control each other. They are found in many household items such as radios, computers, and telephones, and many others. Other semiconductor devices include solar cells, diodes, and LEDs (light emitting diodes).
In 1958 and 1959, two people had the idea for an integrated circuit at almost exactly the same time. Transistors had become an everyday thing used in household devices such as radios. They affected everything from radios to phones and at the time manufacturers needed a smaller replacement for vacuum tubes. Transistors were smaller than vacuum tubes, but for some of the newest electronics, for example missile guidance, they were not small enough.
One day in July, Jack Kilby was working at Texas Instruments when it occurred to him that all parts of a circuit, not just the transistor, could be made out of silicon. At the time, nobody was putting capacitors and resistors into ICs. This would change the future and make it easier to produce and sell integrated circuits. Kilby's boss liked the idea, and told him to get to work. By September 12, Kilby had built a working model, and on February 6, Texas Instruments filed a patent. Their first ""Solid Circuit"" was the size of a fingertip.
Meanwhile, in California, another man had the same idea. In January of 1959, Robert Noyce was working at the small Fairchild Semiconductor startup company. He also realized a whole circuit could be put into a single chip. While Kilby had worked out the details of making individual components, Noyce thought of a much better way to connect the parts. The design was called a ""unitary circuit"." All that detail paid off because on April 25, 1961, the patent office awarded the first patent for an integrated circuit to Robert Noyce while Kilby's application was still being analyzed. Today, both men are acknowledged as having independently conceived of the idea.
Soon there were two kinds of integrated circuit: hybrid (HIC) and monolithic (MIC). Hybrids died out late in the 20th century.
※ The difference between VLSI and ULSI is not well defined.
Integrated circuits can be packaged as DIP (Dual in-line package), PLCC (Plastic leaded chip carrier), TSOP (Thin small-outline package), PQFP (Plastic Quad Flat Pack) and other chip package types. Some small ones are packaged for surface-mount technology. The transistors inside can be bipolar transistors in unusual circuits, such as those needing very high switching speeds. Most, however, are MOSFETs.
Moss
Mosses are bryophytes, a group of plants without tissue to move water. Mosses evolved from liverworts.
Moss tissue does not have cells that move water. This means that they are non-vascular plants. Water must soak into mosses like a sponge. A patch of moss is made of many tiny moss plants packed together so that they can hold water for as long as possible. They do not have roots. Because mosses cannot find water, they live in two ways. They can live in places that are always wet like near a spring, a river, or in a place where there is a lot of fog. They can also pause their natural processes when they dry up. Mosses can survive months in this paused state. However, they eventually need water to live. This means they can never live in dry places like deserts.
Mosses cannot grow very large because they could not move water to the top of their growth. The largest moss grows in New Zealand. It is about 30 cm tall.
A moss does not make seeds. A moss does not have fruit. The green fuzzy part of a moss that is always there has only one set of DNA. Moss waits until there is lots of food and enough water. Then it produces spores that leave the parent plant and float away. The spores are like dust. They will make more moss. Each spore is male or female. It grows into the green fuzzy part of the moss called the gametophyte. Male gametophyte make sperm. Female gametophyte make eggs. Water moves the sperm from the male moss to the female moss. Then the sperm and the egg join to make a cell with two sets of moss DNA. This cell grows into a different shape called a sporophyte. The sporophyte gets all of its food from the green fuzzy female gametophyte. When the sporophyte grows up, it makes a tiny box with spores inside instead of seeds. The lid on the box falls and the spores float away to repeat the cycle again. This process is called alternation of generations.
Scientists divide the mosses into eight groups. Five of these groups are small, with just a few species; most mosses are in the group called Bryopsida.
Function (mathematics)
In mathematics, a function is a mathematical object that produces an output, when given an input (which could be a number, a vector, or anything that can exist inside a set of things).