A computer system is a collection of hardware and software components that work together to run computer programs. Specific implementations of systems change over time, but the underlying concepts do not. All systems have similar hardware and software components that perform similar functions. This book is written for programmers who want to improve at their craft by understanding how these components work and how they affect the correctness and performance of their programs.
In their classic text on the C programming language, Kernighan and Ritchie introduce readers to C using the hello program shown below:
#include <stdio.h>
int main()
{
printf("hello, world\n");
}
Although hello is a very simple program, every major part of the system must work in concert in order for
it to run to completion. We will begin our study of systems by tracing the lifetime of the hello program, from the time a programmer creates it, until it runs on a system, prints its simple message, and terminates. As we follow the lifetime of the program, we will briefly introduce the key concepts, terminology, and components that come into play. Later posts will expand on these ideas. 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 modern systems represent text characters using the ASCII standard that represents each character with a unique byte-sized integer value.
In their classic text on the C programming language, Kernighan and Ritchie introduce readers to C using the hello program shown below:
#include <stdio.h>
int main()
{
printf("hello, world\n");
}
Although hello is a very simple program, every major part of the system must work in concert in order for
it to run to completion. We will begin our study of systems by tracing the lifetime of the hello program, from the time a programmer creates it, until it runs on a system, prints its simple message, and terminates. As we follow the lifetime of the program, we will briefly introduce the key concepts, terminology, and components that come into play. Later posts will expand on these ideas. 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 modern systems represent text characters using the ASCII standard that represents each character with a unique byte-sized integer value.
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. For example, the first byte has the integer value 35, which corresponds to the character ’#’. The second byte has the integer value 105, which corresponds to the character ’i’, and so on. Notice that the invisible newline character ‘\n’, which is represented by the integer value 10, terminates each text line. Files such as hello.c that consist exclusively of ASCII characters are known as text files. All other files are known as binary files. 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. For example, in different contexts, the same sequence of bytes might represent an integer, floating-point number, character string, or machine instruction.