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What is a Virtual Machine?

To understand what a virtual machine is, let’s briefly talk about physical machines. Physical machines can simply be understood as the hardware that runs on your computer.

Imagine EVM as a computer that specializes in handling smart contract transactions as well as defining the rules for state changes from block to block in the Ethereum blockchain. Virtualization is the process of creating a software-based, or “virtual” version of a computer, with dedicated amounts of CPU, memory, and storage that are “borrowed” from a physical host computer—such as your personal computer— and/or a remote server.

However, unlike physical computers, these computers exist in a software environment, not hardware. Virtual machines are software that simulates real computers.

The EVM is a virtual machine that is not bound to a single operating system or location, thus allowing global accessibility for anyone willing to run an Ethereum node. Virtual machines are also platform agnostic, allowing compatibility to a wide range of systems, irrespective of the underlying hardware.

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Few things about the EVM

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EVM is a State Machine

A state machine in simple terms is a device that specializes in storing state as well as defining the rules for state changes of a particular system.

In other words, every detail on the Ethereum blockchain, i.e., the amount of ERC20 tokens you hold and NFT ownership, are technically different states on the network. These states are reducible to a single root hash, which we call the World State. This means that when anything is changed on the Ethereum blockchain, it has to have originated from a transaction.

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EVM as a Quasi-Turing complete machine

Turing complete, named after famous computer scientist Alan Turing, refers to the kind of machine that can solve any computational problem, irrespective of the time or memory it takes to do so. (This assumes we have infinite time or memory.)

For instance, programming languages such as Python, C++, Java, HTML+CSS, and MTG are all turing complete systems.

You would assume that Solidity would also be right?

Kinda**

In the world of Ethereum, we cannot have programs that run forever or use infinite memory. While regular computers can halt such infinitely programs, we cannot do the same with Ethereum as it’s a global computer.

Now in order to avoid the halting issue, there is a type of limitation imposed on every execution on the Ethereum blockchain - Gas.

This means the EVM keeps track of every instruction that is to be executed and charges a particular amount of Gas fees (in ETH) for every computation or storage being used in the transaction.

Gas is a reflection of the amount of state being changed.

Why is the EVM Quasi-Turing complete and not just Turing-Complete? A system is considered Turing-complete if it can simulate any Turing machine, which assumes the availability of unlimited computational resources (time and memory). The EVM has all the necessary computational capabilities to be Turing-complete, but it deliberately implements a gas mechanism that places an upper bound on the number of computational steps that can be executed in a single transaction. This makes it “quasi-Turing complete” - it has the computational power of a Turing machine, but with practical limitations enforced through the gas mechanism to ensure transactions cannot run indefinitely.