The Structure of CPU

The CPU of a modern small computer is physically implemented as single silicon "chip". This chip will have engraved on it the million or more transistors and the interconnecting wiring that define the CPU's circuits. The chip will have one hundred or more pins around its rim. Some of these pins are connection points for the signal lines from the bus, others will be the points where electrical power is supplied to the chip. Although physically a single component, the CPU is logically made up from a number of subparts. The three most important, which will be present in every CPU.

The timing and control circuits are the heart of the system. A controlling circuit defines the computer's basic processing cycle: repeat, fetch next instruction from memory, decode instruction (i.e. determine which data manipulation circuit is to be activated), fetch from memory any additional data that are needed,execute the instruction (feed the data to the appropriate manipulation circuit), until "halt" instruction has been executed.

Along with the controlling "fetch-decode-execute" circuit, the timing and control component of the CPU contains the circuits for decoding instructions and decoding addresses (i.e. working out the location in memory of required data elements).

The arithmetic logic unit (ALU) contains the circuits that manipulate data. There will be circuits for arithmetic operations like addition and multiplication. Often there will be different versions of such circuits – one version for integer numbers and a second for real numbers. Other circuits will implement comparison operations that permit a program check whether one data value is greater than or less than some other value. 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. It is normal for main memory to be large enough to hold millions of data values; the CPU may only have space for something like 16 values. A CPU register will hold as many bits as a "word" in the computer's memory. Most current CPUs have registers that each store 32 bits of data. The circuits in the ALU often are organized so that some or all of their inputs and outputs must come from, or go to, CPU registers. Data values have to be fetched from memory and stored temporarily in CPU registers. Only then they can 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. CPU designs vary with respect to their use of registers. But, commonly, a CPU will have 8 or more "data" registers and another 8 "address" registers.

Vocabulary Notes

to implement ['ImplImqnt] – виконувати, забезпечувати виконання, здійснювати, утілюватись в життя.

to engrave [In'greIv] – утримувати на собі, гравірувати

wiring ['waiqrIN] – монтаж, проводка, монтажна схема

pin – штекер, вивід; контакт

RIM – read-in mode режим вводу

supply – постачати

subpart – підчастина

to define – давати визначення

to determine [dI'tWmIn]– визначати, встановлювати

to feed – надавати інформацію

manipulation – маніпулювання, обробка

to require [rI'kwaiq] – вимагати

addition and multiplication – додавання і множення

comparison [kqm'pxrIsn] – порівняння

to permit ['pWmit] – дозволяти

values ['vxljHs] – величини

current ['kAr(q)nt] – сучасний

register ['reGistq] – регістр

calculation – обчислення

reserve [rI'zWv] – резерв, зберігати