1.10. Read and translate the text

COMPUTER STORAGE FUNDAMENTALS

Data are processed and stored in a computer system through the presence or absence of electronic or magnetic signals in the computer's circuitry in the media it users. This is called a "two-state" or binary representation of data, since the computer and the media can exhibit only two possible states or conditions. This binary characteristic of computer circuitry and media is what makes the binary number system the basis for representing data in computers. Thus, for electronic circuits, the conducting (ON) state represents the number one, while the nonconducting (OFF) state represents the number zero. For magnetic media, the magnetic field of a magnetized spot in one direction represents a one, while magnetism in the other direction represents a zero.

The smallest element of data is called a bit, or binary digit, which can have a value of either zero or one. The capacity of memory chips is usually expressed in terms of bits. A byte is a basic grouping of bits that the computer operates as a single unit. Typically, it consists of eight bits and represents one character of data in most computer coding schemes. Thus, the capacity of a computer's memory and secondary storage devices is usually expressed in terms of bytes. Computer codes such as ASCII (American Standard Code for Information Interchange) use various arrangements of bits to form bytes that represent the numbers zero through nine, the letters of the alphabet, and many other characters.

Storage capacities are frequently measured in kilobytes (KB), megabytes (MB), gigabytes (GB), or terabytes (TB).

The primary storage (main memory) of your computer consists of microelectronic semiconductor memory chips. Memory chips with capacities of about 300 gigabytes are now common. The capacity of a computer is the quantity of data that its memory unit can hold. Plug-in memory circuit boards containing 16 or 32 megabytes or more of memory chips can be added to your PC to increase its memory capacity. Specialized memory can help improve your computer's performance. Examples include external cache memory of 256 or 512 kilobytes to help your microprocessor work faster, or a video graphics accelerator card with 2 megabytes or more of RAM for faster and clearer video performance. Removable credit-card-size and smaller "flash memory" RAM cards can also provide several megabytes of erasable direct access storage for PDAs or handheld PCs.

Some of the major attractions of semiconductor memory are its small size, great speed, and temperature resistance. One major disadvantage of most semiconductor memory is its volatility. Uninterrupted electric power must be supplied or the contents of memory will be lost. Therefore, emergency transfer to other devices or standby electrical power (through battery packs or emergence generators) is required if data are to be saved. Another alternative is to permanently "burn in" the contents of semiconductor devices so that they cannot be erased by a loss of power.

Thus, there are two basic types of semiconductor memory: random access memory (RAM) and read only memory (ROM).

RAM: random access memory. This is a poor term, since all main memory has the property of random access. A better term would be read-write memory; the most likely reason why this term is not used is that its acronym, RWM, is unpronounceable. Users work with the random-access-memory (RAM). RAM is a collec­tion of cells and we can access any cell at any given time, hence the name random access memory.

RAM is often referred to as main memory or primary storage. RAM usually occupies a number of chips connected together. It is used to store programs and data being used by these programs while the computer is on. When the computer is turned off any information is erased from the RAM. That is why RAM is often called volatile while ROM is a non-volatile type

of memory.

As we have already mentioned this is a volatile memory. Because your most current computer work is stored in RAM, this is why you lose your most recent typing at the computer when your computer crashes or the electricity goes out. The need often arises, however, to store some programs permanently in main memory. The bootstrap program that starts up the computer when it is first turned on is a case in point. Some computers provide permanent storage for operating system and frequently used programs such as language processors and word processors, thus assuring that these will be ready for immediate use when the computer is turned

on.

To facilitate quick access for processing, a typical modern computer has a main memory connected by a memory bus directly to the processor. Random access memory is much faster to read from and write to than the other kinds of storage devices in a computer such as the hard disk, and CD-ROM.

Read-only-memory (ROM) is a chip or a group of chips containing programs, tables of constants and instructions for the CPU. Only the CPU has access to this memory. For example, when we turn on the computer, the CPU gets its first instructions from the ROM. These instructions are burnt into the chip with the help of special equipment before the chip is installed inside the computer. Users do not have access to the ROM, so they cannot change these instructions.

Nonvolatile random access memory chips are used for permanent storage. ROM can be read but not erased or overwritten. Frequently used control instruction in the control unit and programs in primary storage (such as parts of the operating system) can be permanently burned in to the storage cells during manufacture and cannot be erased once they are programmed or loaded with specific instructions. This is sometimes called firmware, which is "hard" software. Variations include FROM (programmable read only memory) and EPROM (erasable programmable read only memory) that can be permanently or temporarily programmed after manufacture.

Computer chips are designed to serve several different kinds of memory needs. Though RAM and ROM are the most common forms of computer memory chips, there are other forms of memory:

EPROM is Erasable Programmable Read Only Memory. These chips allow the user to store data that will not be lost when electrical power to the computer stops, but through various techniques can be quickly erased to start over again. This is known as nonvolatile memory. These are sometimes referred to as Flash chips because they can be erased in a flash, yet hold data when the power is off.

MRAM is Magnetic Random Access Memory, which uses the magnetic spin of electrons instead of power refreshing to hold the electrical signal of one or zero. This is another form of nonvolatile memory which allows: immediate start up without booting software from a hard drive; greatly reduce battery usage; store more data in the same chip space; and provide faster access to data. When purchasing additional RAM for a computer, the computer manual that ships with your computer will tell you which kind you need. These chips might be titled SIMMs or DIMMs chips and new types will emerge.