File Descriptors, I/O Redirection, Processes, Network Programming and Concurrency

I like to understand how things work (together) by asking myself questions. So let’s get started.

Question 1: What is input/output?

Input/output(I/O) is the process of copying data between 1) main memory and 2) external devices such as disk drives, terminals, and networks.

1 ) An input operation copies data from an I/O device to main memory.

2 )An output operation copies data from memory to a device.

We can also say Input/output(I/O) is the process of copying data between a program/process and the external device. The reason for saying that is

1) the CPU is the one reads&interprets the machine-language instructions stores in main memory.

2 ) In the perspective of CPU, keyboard, mouse, display, disk drives, networks are all I/O devices.

Question here to ask: how to move data between 2/multiple processes?

Question 2: Why does a process need to know file descriptors?

All I/O routines centered on file descriptors.

A process performs input & output by calling the read and write functions respectively.

Every process has a current working directory. That’s why your process can refer to a specific file that relative to the current working directory.

A process opens an existing file or create a new file by calling the open function.

Sharing resources between multiple processes.

Question 3: Each process created by a Linux shell begins life with three open files: standard input (descriptor 0), standard output (descriptor 1), and standard error (descriptor 2). So where do these 3 files reside?

Reference:

Data transfer between processes

https://www.mcs.anl.gov/papers/icpp06-smp-xfer.pdf

Introduction to Linux IO Redirection

https://www.digitalocean.com/community/tutorials/an-introduction-to-linux-i-o-redirection