What is a bit? Why do computers only understand 0 and 1?

Bit stands for Binary Digit. There are only two binary digits, i.e., 0 and 1.

Our mathematics starts from 0 and ends at 9. Then we take the first number, “0”, and put the following number, “1”, before it. It gives us 10, and then we count again from 0 to 1, reaching 19, and then we change the first digit again.

However, for computers, there are only two numbers, namely 0 and 1. So, if they have to count, they’ll have to use only these two numbers. They start with “0” and then proceed to “1”. After that, they retake “0” just like us and put the “1” behind it. The third number becomes 1,0, and the fourth becomes 11. Again, because the numbers are finished, we take two 0’s and put 1 behind it.

This is how computers calculate things. Everything inside computers is represented, calculated, manipulated, stored, and processed in the form of numbers.

For example, to store a picture, the computer must check each pixel and its corresponding color. The color is then converted into a binary code (typically RGB values) and stored in the temporary or permanent memory. This is done for each pixel, and this can easily become hundreds of thousands of bits for a single picture, depending on its size. If the system needs to store it, the request is sent to the permanent storage drive (SSD or HDD) along with the location address, allowing it to be retrieved when needed.

What is a bit?

The bit is the smallest unit of data a computer can work with. It can be either 0 or 1. Whether it is a music file, video file, text file, or image file, everything is understood, processed, stored, and edited by the computer in the form of bits. There are various conversion methods for different file types, but ultimately, our computers store vast numbers of bits, even for small files.

Output devices, such as our monitor, receive the color signal in the form of bits as well. Input devices, such as the mouse, send movement signals through light in the form of bits. The CPU processes everything in the form of bits, but we can’t see how it is happening with our eyes. The scale of operation, even for a slight mouse movement, is quite substantial. The difference in position must be sent to the CPU, and it should then send the same signal back to the monitor. Leave aside the complexity of doing tasks like video editing.

However, for the computer, it is just a large circuit that turns On and Off at different points. Billions of these points are present in a single CPU, and a complex system controls each one to provide the software with a platform to run.

For humans to understand and work with these circuits, bits are like abstractions. Older computers used to work with the help of physical switches, where we turned the switches on and off manually.

But, as the technology advanced, we added a layer of software to make programming the computers easier. If you have to program a computer from its very basics, you must understand the machine code. A machine code is converted into binary bits, and then processing is performed according to the commands. However, because we have the operating system and numerous software programs for various tasks, we don’t really know what is going on under the hood. We will talk about the role of software later on.

Example Machine Code (Human Language) converted into bits (Computer Language)

Let’s write a machine code to add two digits. Let’s then convert it to binary form so that we can understand how computers understand humans and perform their tasks.

Our code has a simple instruction ‘Add A, B‘. This instruction means the computer will add the value stored in register A and register B.

The ADD instruction here also has its own binary Opcode, i.e., 0001. The Opcode for Register A is 01, and Register B is 10.

So, when we put all these instructions into the binary code, it will become 0001 01,10

The CPU now knows that the 0001 commands indicate addition logic. It will then check the following numbers i,e, 01, and 10. The full machine code in binary form will become 0001 0110.

The CPU reads the binary sequence 0001 0110, decodes it as an ADD operation involving registers A and B, and then performs the addition.

Just like this, big programs are run, but everything will be converted into binary form first of all.

From Bits to Video (Hierarchy)

Why only two bits?

Computers work with the help of electronic circuits. To solve any problem or run a command, the computer must have some kind of logic. For example, to add 1 to another 1, there must be a circuit that can create two as the output. For this, we can make a circuit that takes two inputs in the form of high or low voltage. Depending on that input, we can design the circuit to give one or two outputs. The circuits are designed in a way that allows us to manipulate them with the help of code (called software). The circuits are always already designed.

The purpose of using two bits is to use the power of electronics to do calculations with the highest level of accuracy.

An electric circuit can be turned on or off at a time. So, we just get two different levels of values, which can be represented as On/Off, High/Low, or +/-.

For example, if a circuit gets some input or inputs as 0s and 1s or high/low voltage, the resulting values can be interpreted in the same manner. A single circuit can be designed to yield different values based on the input values. It could output 1 with “0 0” as input, or 0 with “1 1” as input. There is a master clock that can be used to feed different circuits, get outputs, and then give inputs from other outputs.

The issue is that we have only two values, which makes our circuits both large and simple. We may have to work with thousands of bits at a time, but because there are only two values, the speed of operation and accuracy increase a lot.

Physical Representation of a Bit

Bits are only in our minds. There are no actual 0s and 1s inside our CPU. There is only current flowing in all directions, and there are circuits that either allow or block this flow. The physical representation of bits varies across different computer components.

The CPU primarily uses the state of transistors, i.e., on or off, to represent the bits. If we have to add two bits, there must be some operations inside the transistors.

Inside the RAM, bits are stored primarily as electric charges within the capacitors.

Inside the SSDs, the bits are stored in the form of an electric charge in floating gate transistors. Each floating gate transistor can also hold more than one bit.

Inside the hard drives, there are magnetic domains that represent the values of the bits, either 0 or 1.

In optical media such as DVDs and CDs, bits are represented by pits and lands on the disk’s surface.

Therefore, there are various methods to represent a bit so that we can interpret it for our benefit. All these storage media must also be able to interact with the CPU and with each other. The faster the speed of this interaction, the lower the bottlenecks will be.

The CPU is the brain that controls everything from processing to storing data. Inside the CPU, bits are just the voltage levels inside transistors. These transistors function as switches that can either allow or block the flow of electrical current. When a transistor is “on,” it allows current to pass through, which is typically interpreted as a binary 1. When it is “off,” it blocks the current, which is interpreted as a binary 0.

• High Voltage: Represents a binary 1.
• Low Voltage: Represents a binary 0.

The exact voltage levels depend on the technology used (e.g., CMOS, TTL), but the principle remains the same: distinct voltage thresholds define the 0 and 1 states.

How does the computer do calculations using 0s and 1s?

Computers utilize logic gates to perform their tasks. Logic gates are composed of electronic components, including MOSFETs, BJTs, diodes, resistors, capacitors, and power supplies. In digital electronics, these operations are referred to as AND, OR, NOT, NAND, NOR, XOR, and XNOR operations.

We don’t have to delve too deeply into this, but I will give you a brief idea of how the calculations and processing are done inside computers.

The CPU, or Central Processing Unit, is the central processing unit. It processes, modifies, stores, transmits, and performs various operations on the data. There is a memory component alongside the CPU that assists with processing. Each operation is performed in a four-step cycle: Fetch, Decode, Execute, and Store. This process begins by retrieving information from memory, decoding the instruction, and interpreting the action. The necessary action is done, and the result is stored back in the memory.

All these instructions, along with the data to be processed and stored, are in binary form. It means that whatever you are doing on your computer is converted into a set of data in the form of actual data, and the instructions are all in binary digits.

However, all the calculations and operations adhere to the very popular mathematics concept called Boolean algebra. With the help of logic gates combined with Boolean algebra, we can do things like additions, subtractions, multiplications, etc.

A basic mathematical calculation in binary is like this:

• 0 + 0 = 0
• 0 + 1 = 1
• 1 + 0 = 1
• 1 + 1 = 10 (which is 0 with a carry of 1 to the next bit).

Now, these numbers can be converted into different steps, but ultimately, it all comes down to basic logical operations like these.

Role of software

It is impossible to understand how computers work without knowing the software. A computer without software is just like a big circuit ready to do things. It is simply waiting for commands to take action. This command must also be in binary form. However, we interact with computers through the use of human-understandable code. We use high-level languages to give instructions to computers, but the laptop first converts them to binary, which is its native language.

We generally think that there are things a computer does on its own, and there are things we tell it to do. But there is nothing a computer can do on its own. Everything, from mouse movements to booting, is controlled and executed by the software. Hardware is like a giant circuit that can be programmed with the help of software.

The same CPU can be used to play games, edit videos, and run Google Chrome. How is that possible? This is happening because a circuit can be programmed and reprogrammed to do different things. Each pixel on your display gets its signal from the computer. Each mouse movement changes the color of your display in the same arrow shape.

We think we are typing texts only on the monitor. But the computer is changing the white pixels to black pixels. The text editor, like Microsoft Notepad, provides you with a white space on which you type. The input values from the keyboard are sent to the CPU first, and then they are displayed on the notepad. However, for Notepad to function, there is another layer of the operating system that interacts with the hardware in real-time.

Role of bits in CPU operations

The CPU performs operations known as bitwise operations. These operations are done with the help of logic gates such as AND, OR, XOR, and NOT. All the data processed by the CPU, whether characters, numbers, or instructions, is represented in bits. The CPU reads this data from memory and performs the necessary operation as specified in the instructions. It can then write the result back into the memory.

The CPUs work along with small memory locations called Registers. These registers store the temporary data required for all CPU operations. Each register can hold a set of bits, typically 32 bits or 64 bits.

There are control signals in the CPU that are also represented in the form of bits. Their role is to direct the flow of data between different parts of the CPU.

Role of bits in memory and storage

As we discussed above, everything is processed in the form of bits in the computer. Also, everything is stored in the form of bits as well. There are just high and low levels of voltage that discriminate the 0 and 1 values. In the memory or RAM of your computer, the bits are stored inside capacitors and retrieved by the CPU from there. RAM is the nearest and fastest type of memory for the CPU after the cache and registers. But it generally has a bigger capacity than the CPU does. Therefore, the items that are no longer necessary in the registers are sent to memory. But everything is sent in the form of bits, and the RAM clears them as soon as the power is turned off.

In permanent storage devices like SSDs, Hard Drives, and flash drives, the bits are stored in locations where they can remain without the need for power. Inside SSDs, flash drives, external SSDs, and SD cards, data is stored in NAND flash memory. This is a type of permanent memory that utilizes floating gate transistors or charge-trap flash. However, in hard drives, the data is stored in magnetic platters in the form of different magnetic fields.

Because the CPU works with bits, memory, and storage, it keeps them in a way that the CPU can use them whenever required. Similarly, the CPU can send data in the form of bits to these storage media.

Conclusion

Understanding the concept of bits is essential to know how computers work. However, there is no serious need to know this unless you are working as a hardware designer, driver developer, operating system programmer, etc. Bits are a fundamental concept in digital electronics. I hope I have given you a basic idea of what these bits are.