Comparison between input and output devices and also an elaboration on data transfer

What are input and output devices? Why are they so important when it comes to using our computers. Though, we may fail to realize it, the very mouse, keyboard and screen we are using are all parts of either of these two categories. Even the headset or speaker, the microphone, printer and so on... are all a part of either of these categories. So, what defines something to be an input device and the rest to be an output device. And most of all, why are these different from each other? For that, we have to take a look at a broader explanation of what these two terms actually are.

What is an input device and what are some examples?

Input refers to giving or providing a computer system with some piece of data. Hence, a piece of equipment that provides data and control signals to an information processing system like a computer is called an input device. Input devices can be categorized because of their various functionalities. Some may provide the computer mechanical motion information, like a mouse or joystick. While others may provide an audio or video signal to the computer e.g., a webcam or microphone. Some examples would be:

• Mice
• Keyboards
• Microphones
• Touch-pads
• Joysticks
• Webcams
• Fingerprint scanners
• Document scanners

A keyboard, which is also an input device.

How about some output devices? What are they?

A piece of computer hardware or equipment which converts information into human readable form. It can be text, graphics, audio and video. Like, the screen or monitor we're looking at is an output device that outputs graphics. While the headphones we are probably using is outputting sound. Or something like a printer that outputs text. Some examples would be:

• Monitors
• Printers
• Speakers
• Headphones
• Projectors
• OMR

This is what a television from the 90s would look like. (Ignoring the furniture, haha)

 So what's the difference?

In simple words, any sort of device that we use to do something inside the computer interface or instruct the computer to do something is most likely an input device. While, the computer translating something for us or showing something to us or making it readable for us after going through a processing period is pretty likely an output device. In other words, if we use something to instruct the computer, that's an input device. On the other hand, whatever gives us the results of those instructions is very likely an output device. It's as simple as that.

What about a SD card? And what process is used to get the data inside the computer?

A SD card actually classifies as neither, instead this is a completely different category. An SD card is considered as a storage device. To be more precise, an external secondary storage, that is non-volatile. When it comes to data transfer however, computers and smartphones transfer data from an SD card quite similarly but using different interfaces. Computers usually use a card reader while smartphones probably do it using PCIe. 

As suggested by the name Universal Serial Bus, data transmission in the bus occurs in a serial form. Data are broken up into bytes and sent along the bus one bit at a time, with the least significant bit first as illustrated:

Serial data transmission

 

This data is sent across in packets. Each packet is basically a bundle of data along with the information about the source, destination and length of the data, and also error detection information.  When the software requires data transfer to occur between itself and the USB, it sends a block of data called an I/O Request Packet (IRP) to the appropriate bus/pipe, and the software is later notified when this request is completed successfully or terminated by error.
This is how data within the SD card is both read and written (R/W).

These are all types of SD cards.