Transcript 知识管理的IT实现 IBM知识管理解决方案

Passage Two.
How Does A Computer Work?
Training target:
In this part，our target is to train your reading speed. You
should pay more attention to “word group”. Treating a group of
words as a whole unit is a short cut to you’re your time. We have
underlined the word groups in some sentences，and the rest can be
practiced by yourself. If there are some new words，you may cover
the note area with a piece of paper and try to guess their meanings
without looking them up in the dictionary.
 Text
 The basic building block of a modern computer is a chip，
a complex，integrated electronic circuit etched on a
tiny square of silicon no bigger than a fingernail.
Since individual chips are fragile and difficult to
handle，they are normally packed and mounted on
boards. A computer is assembled by sliding the right
boards into a machine box. One board might hold the
processor，which in fact is the heart of a computer;
another might hold memory store which provides the
computer with data and instructions; while the third
might hold the electronics to link a particular input
device or output device to the system.
..
 Let us use the system shown in Pic2.3 to show
you how a typical computer works.A computer is
controlled by a stored program，so if we want to
use a computer，the first step is copying the
program from diskette into memory. Now the
processor can begin executing instructions; the
data input from the keyboard are stored in
memory. The processor processes the data and
then stores the results back into memory. At last，
we can get the result.
Pic 2.3
. Now we can see that a computer system consists
of four basic components. An input device
provides data. The data are stored in memory，
which also holds a program. Under the controls
of the program，the computer’s processor
processes the data. The results flow from the
computer to an output device. Let us come closer
to the system components one by one，
beginning with the processor.
 .The processor，usually called the central processing unit
（CPU）or main processor，is the heart of a computer. It
is the CPU that in fact processes or manipulates data and
controls all the rest parts of the computer. How can it
manage its job? The secret is software. Without a
program to provide control，a CPU can do nothing. How
can a program guide the CPU through the processes? Let
us consider from the basic element of a program—
instruction. An instruction is composed of two parts: an
operation code and one or more operands.The operation
code tells the CPU what to do and the operands tell the
CPU where to find the data to be manipulated.
.
 The processor contains four major components:a
clock，an instruction control unit，an arithmetic
and logic unit（usually shorted for ALU），and
several registers. The clock generates precisely
timed pulses of current that synchronize the
processor’s other components. Then the
instruction control unit determines the location of
the next instruction to be executed and fetches it
from the main memory.
.
 The arithmetic and logic unit performs arithmetic
operations（such as addition and subtraction）
and logic operations（such as testing a value to
see if it is true or false），while the registers are
temporary storage devices that hold control
information，key data and some intermediate
results. Since the registers are located in the
CPU，the processing speed is faster than the
main memory.
.
 Then which is the key component to a
computer’s speed? It is the clock! In more detail，
it is the clock’s frequency that decides a
computer’s processing speed. When we buy a
computer，we usually consider the main
frequency first，and that means a clock’s
frequency.
.
 Now we will talk more in detail about the
Microprocessors and Central Processing Units
（Pic2.6）.Microprocessors are central processing units
etched on a tiny chip of silicon and，thus，are called
microchips. Microprocessors contain many electronic
switches，called transistors，which determine whether
electric current is allowed to pass through or not.
Transistors are the basic building blocks of
microprocessors. A single microchip may contain millions
of transistors. When electric current is allowed to pass
through，the switch is on. This represents a1bit.If the
current does not pass through，the switch is off. This
represents a0bit.Different combinations of transistors
represent different combinations of bits，which are used
to represent special characters，letters，and digits.
.

When we talk about the computer，we usually
meet the topic: motherboard（Pic2.7）.The main
circuit board in a computer is called the
motherboard. It is a flat board that holds all of the
key elements that make up the“brain”of the
system，including the microprocessor or CPU，
RAM（electronic or primary memory），and
expansion slots which are sockets where other
circuit boards called expansion boards may be
plugged in.
Pic 2.6 CPU
Pic 2.7 motherboard

The End