Chapter 1: A Tour of Computer System

1.1 Information is Bits + Context

本节主要介绍了文件信息在计算机系统中是以什么形式存储的，比如我们的hello.c源文件，在计算机系统中是如何识别每个字符。

#include <stdio.h> 

int main() 
{
	printf("hello, world\n");
	return 0; 
}

Our hello program begins life as a ==source== program (or source ﬁle) that the programmer creates with an editor and saves in a text ﬁle called hello.c.
The source program is a sequence of ==bits==, each with a value of 0 or 1, organized in 8-bit chunks called ==bytes==.
Each ==byte== represents some text character in the program.
Most computer systems represent text characters using the ==ASCII== standard that represents each character with a unique byte-size integer value.

![[./1_1.assets/Screenshot 2023-10-04 at 15.27.00.png]]
The hello.c program is stored in a ﬁle as a sequence of ==bytes==. Each byte has an integer value that corresponds to some character.

![[./1_1.assets/Screenshot 2023-09-26 at 12.46.04.png]]
```
ascii value of '#' = 35 
value in bits: 0b 0010 0011

ascii value of 'i' = 105 
value in bits: 0b 0110 1001

ascii value of 'n' = 110 
value in bits: 0b 0110 1110

...
```
- finally it will be a binary file in computer system:
```
0010 0010 0110 1001 0110 1110 ...
```
The representation of hello.c illustrates a fundamental idea: All information in a system—including disk ﬁles, programs stored in memory, user data stored in memory, and data transferred across a network—is represented as a bunch of ==bits==. The only thing that distinguishes different data objects is the context in which we view them.
```
0b 0110 1110 can be 110 in integer, 'n' in character ...
```