A computer contains several major subsystems --- such as the Central Processing Unit(CPU), memory, and peripheral device controllers. These components all plug into a "Bus". The bus is essentially a communications highway; all the other components work together by transferring data over the bus.
Instructions and data are stored in main memory. The CPU fetches them as needed. Peripheral device controllers look after input devices, like keyboards and mice, output devices, like printers and graphics displays, and storage devices like disks. The CPU and peripheral controllers work together to transfer information between the computer and its users. Sometimes, the CPU will arrange for data be taken from an input device, transfer through the controller, move over the bus and get loaded directly into the CPU. Data being output follows the same route in reverse – moving from the CPU, over the bus, through a controller and out to a device.Commonly, CPUs are designed to work efficiently with both two-byte integers and four-byte integers
CPU ( central processing unit)
The CPU of a modern small computer is physically implemented as single silicon "chip". Although physically a single component, the CPU is logically made up from a number of subparts.They are principle components of CPU (timing and control circuits, arithmetic logic unit and high speed register storage).
• The timing and control circuits are the heart of the system. A controlling circuit defines the computer's basic processing cycle (fetch, decode, execute Cycle).
• Circuit for operation of arithmetic logic unit(ALU) like addition and multiplication. There will be different versions of such circuits – one version for integer numbers and a second for real numbers. There will also be "logic" circuits that directly manipulate bit pattern data.
• While most data are kept in memory, CPUs are designed to hold a small amount of data in "registers" (data stores) in the CPU itself. Most current CPUs have registers that each store 32 bits of data. Data values have to be fetched from memory and stored temporarily in CPU registers. Only then can they be combined using an ALU circuit, with the result again going to a register. If the result is from the final step in a calculation, it gets stored back into main memory. While some of the CPU registers are used for data values that are being manipulated, others may be reserved for calculations that the CPU has to do when it is working out where in memory particular data values are to be stored.
Memory and data
- Computers have two types of memory:
ROM – Read Only Memory: ROM memory is generally used to hold parts of the code of the computer's operating system.
RAM – Random access Memory: Most of the memory on a computer will be RAM. RAM memory is used to hold the rest of the code and data for the operating system, and the code and data for the program(s) being run on the computer.
Memory sizes may be quoted in bits, bytes, or words: Bit a single 0 or 1 data value , Byte a group of 8 bits Word the width of the primary data paths between memory and the CPU, maybe 16-bit (two byte), 32-bit (four byte) or larger. To store individual bits, the most popular technology for a computer's main memory used small loops of magnetic oxide ("cores") that could be set with differing North/South polarity to distinguish the 0/1 bit state.
- All data manipulated by computers are represented by bit patterns. A byte, with 8 individual bits, can represent any of 256 different patterns. Bit patterns can also be used to represent numbers. Computers work with integer numbers and "floating point" numbers. A set of 256 patterns is large enough to have a different pattern for each letter of the alphabet, the digits, punctuation characters, and a whole variety of special characters. If a program has to work with textual data, composed of lots of individual characters, then each character can be encoded in a single byte.
A single byte can only be used to encode 256 different values. Two-byte integers are sufficient if a program is working with numbers in the range from about minus thirty thousand to plus thirty thousand; the four-byte integers cover the range from minus to plus two thousand million. When using two bytes, the patterns used to represent integers can be regular patterns in order to make it practical to design electronic circuitry that can combine patterns and achieve effects equivalent to arithmetic operations. Most use a standard character encoding scheme known as ASCII.Although standardized ,The assignments of patterns to characters is essentially arbitrary.But regular pattern (coding schemes) is the most commonly used for integer.
Bus
A computer's bus can be viewed as consisting of about one hundred parallel wires. Some of these wires carry timing signals, others will have control signals, another group will have a bit pattern code that identifies the component (CPU, memory, peripheral controller) that is to deal with the data, and other wires carry signals encoding the data. Transmission of information is controlled by clocks that put timing signals on some of the wires. Information signals are encoded on to the bus, held for a few clock ticks to give all components a chance to recognize and if appropriate take action, then the signals are cleared.
The clock that controls the bus may be "ticking" at more than one hundred million ticks per second .The "plugs" that attach components to the bus incorporate quite sophisticated circuits.
CPU ( central processing unit)
The CPU of a modern small computer is physically implemented as single silicon "chip". Although physically a single component, the CPU is logically made up from a number of subparts.They are principle components of CPU (timing and control circuits, arithmetic logic unit and high speed register storage).
• The timing and control circuits are the heart of the system. A controlling circuit defines the computer's basic processing cycle (fetch, decode, execute Cycle).
• Circuit for operation of arithmetic logic unit(ALU) like addition and multiplication. There will be different versions of such circuits – one version for integer numbers and a second for real numbers. There will also be "logic" circuits that directly manipulate bit pattern data.
• While most data are kept in memory, CPUs are designed to hold a small amount of data in "registers" (data stores) in the CPU itself. Most current CPUs have registers that each store 32 bits of data. Data values have to be fetched from memory and stored temporarily in CPU registers. Only then can they be combined using an ALU circuit, with the result again going to a register. If the result is from the final step in a calculation, it gets stored back into main memory. While some of the CPU registers are used for data values that are being manipulated, others may be reserved for calculations that the CPU has to do when it is working out where in memory particular data values are to be stored.
Memory and data
- Computers have two types of memory:
ROM – Read Only Memory: ROM memory is generally used to hold parts of the code of the computer's operating system.
RAM – Random access Memory: Most of the memory on a computer will be RAM. RAM memory is used to hold the rest of the code and data for the operating system, and the code and data for the program(s) being run on the computer.
Memory sizes may be quoted in bits, bytes, or words: Bit a single 0 or 1 data value , Byte a group of 8 bits Word the width of the primary data paths between memory and the CPU, maybe 16-bit (two byte), 32-bit (four byte) or larger. To store individual bits, the most popular technology for a computer's main memory used small loops of magnetic oxide ("cores") that could be set with differing North/South polarity to distinguish the 0/1 bit state.
- All data manipulated by computers are represented by bit patterns. A byte, with 8 individual bits, can represent any of 256 different patterns. Bit patterns can also be used to represent numbers. Computers work with integer numbers and "floating point" numbers. A set of 256 patterns is large enough to have a different pattern for each letter of the alphabet, the digits, punctuation characters, and a whole variety of special characters. If a program has to work with textual data, composed of lots of individual characters, then each character can be encoded in a single byte.
A single byte can only be used to encode 256 different values. Two-byte integers are sufficient if a program is working with numbers in the range from about minus thirty thousand to plus thirty thousand; the four-byte integers cover the range from minus to plus two thousand million. When using two bytes, the patterns used to represent integers can be regular patterns in order to make it practical to design electronic circuitry that can combine patterns and achieve effects equivalent to arithmetic operations. Most use a standard character encoding scheme known as ASCII.Although standardized ,The assignments of patterns to characters is essentially arbitrary.But regular pattern (coding schemes) is the most commonly used for integer.
Bus
A computer's bus can be viewed as consisting of about one hundred parallel wires. Some of these wires carry timing signals, others will have control signals, another group will have a bit pattern code that identifies the component (CPU, memory, peripheral controller) that is to deal with the data, and other wires carry signals encoding the data. Transmission of information is controlled by clocks that put timing signals on some of the wires. Information signals are encoded on to the bus, held for a few clock ticks to give all components a chance to recognize and if appropriate take action, then the signals are cleared.
The clock that controls the bus may be "ticking" at more than one hundred million ticks per second .The "plugs" that attach components to the bus incorporate quite sophisticated circuits.
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