First, let us discuss Analog Communication.

Here is Transmitter, which transmits 0V to 10V, and the receiver receives 0V to 10V.

If the transmitter transmits 5.6V, then the receiver will receive 5.6V

If the transmitter transmits 5.45V, then the receiver will receive 5.45V

If the transmitter transmits 2.175V, then the receiver will receive 2.175V

For example, we are trying to send numbers between 0 to 1000, and then we can divide the 10V by 1000. We get .01V. The below Table explains this.

Advantages:

Using one single wire, we could transmit any number at one shot. So Information is transmitted at the fastest rate.

Disadvantages

The transmit voltage may not be received by the receiver correctly. For example, if the transmitter sends 2.10V (Number 210), The receiver may receive 2.07V (Number 207). So the information transmitted by the transmitter may not be received by the receiver. This may be due to the voltage loss in the wire/connectors etc. So if you want to transmit accurate information, the Analog may not be the right one. In Analog Transmission, data Integrity is missing.

Now let us discuss Digital Communication.

Here is Transmitter, which transmits 0V or 10V, and the receiver receives 0V or 10V.

Since we can send only 0V or 10V, we can send only two numbers, 0 or 1. We can not send other numbers. If you want to send more numbers, then you need to add more wires. Now we have added one more wire. So now we have two wires. We named them D0 and D1.

Since we have 2 wires, we can transmit up to 4 numbers. Let us see this in the below table.

If you want to send more than 4, then you need to add another wire.

Since we have 3 wires, we can transmit up to 8 numbers. Let us see this in the below table.

So if you like to transmit more numbers, then you will have to add more wires. So let us see that on a table.

So if you want to send numbers up to 65535, then you need 16 wires.

Advantages:

Since we send only two levels, even if there is a slight voltage change in the transmission medium, the number sent by the transmitter will be received by the receiver properly. If 0V changed 1V or 10V changed to 9V, nothing happens.

Disadvantages

Need more wires to send big numbers. This involves cost, Space, and complexity.

To overcome these problems, i.e., One wire (Analog communication advantage) and Data integrity (Digital Communication advantage), Engineers found a method. But they compromised something. Let us discuss that next.

Serial Digital Communication

Now let us have one wire digital communication.

If you wish to transmit number 85, then you need to convert that into binary.

Decimal 85 = Binary 1010101 (64 + 0 + 16 + 0 + 4 + 0 +1).

This is a 7-bit number. Normally in digital transmission, we need 7 wires. But now we have only one wire. So we can transmit only one bit at a time.

So first we transmit 1, after some time 0, after some time 1, then 0, then 1, then 0, then 1. But, of course, that “sometimes” depends on the transmitting media, Wire size, the distance between transmitter and receiver, etc.

Now let us see the timing diagram. i.e., how much time the transmitter takes to transmit number 85 to the receiver.

If we take 1 second to transmit every bit, we take 7 seconds to transmit the number 85.

If we take 1 millisecond, then we take 7 milliseconds.

If we take 1 microsecond, then we take 7 microseconds.

So we are using a unit called bits/second to measure the speed of information exchange. Now days will be hearing 100Mbits/sec, 1Gbits/sec, etc. In Optical fiber, 100Gbits/sec is common now. So they are trying for 400Gbits/sec.

Conclusion:

Analog communication is Fast, but Information Integrity is lost.

Digital Communication (Parallel) is good in information integrity, but more wires are required.

Digital Communication (Serial) is good in information integrity, with only one wire but slow information interchange.

But Industry accepted the Serial Digital communication for data exchange.

For Example:

USB - Universal Serial Bus

SATA - Serial ATA

PCI Express - Serial PCI.

Ethernet - Serial Data transmission.

SPI - Serial Peripheral Interconnect’

I2C - Serial Data transfer.

UART - Universal Asynchronous (Serial) Receiver Transmitter

Today Parallel Digital data communication is used only in the Microprocessor - Memory Interface. But in PC motherboards, the Microprocessor - BIOS ROM interface is Serial (SPI) only. Because after booting, the Microprocessor uses only RAM (DDR DRAM).

If you still need any clarification, please write a comment.

All the best