Internet Computer Canisters are an evolution of smart contracts running at web speed, providing a completely revolutionary smart contract experience for users.
Canisters are the building blocks of the Internet Computer.

They have all the qualities of a traditional smart contract plus added functionalities and memory to store software & user data, so they are a further evolution of smart contracts. Canisters can scale up based on the application load and can call other canisters and serve hundreds of user requests concurrently.
This gives them the unique advantage of achieving thousands of transactions per second, a throughput that can blow Ethereum away and present a practical case for hosting Future DeFi applications.
Canister Software is similar to Software Applications that are built on the Internet Computer(on-chain ) instead of Big Tech Clouds like AWS, Google, Azure, etc. Ex: DSCVR - A Decentralized alternate to Reddit.
Users can interact with canisters through their browser on a PC or cellphone and therefore directly interact with the blockchain rather than communicate with various frontends hosted on Cloud providers like AWS, Azure & Google.
Canisters are loaded with Cycles(gas) for Computation.

ICP tokens are used to mint cycles burned by canisters for computation, which acts as a deflationary force. Cycles' value will always remain stable irrespective of the ICP token price (One of the most significant disadvantages of Ethereum is high gas prices), making canister developer's costs predictable and consistently low.
Cycles can be sent to a canister, which the canister can use later as it performs computations or stores data.

Price of cycles :1 trillion Cycles = 1 CHF (Swiss Franc) of ICP token
Consequently, As the Internet Computer ecosystem is used > More canisters will be built > More Cycles will burn > ICP Token supply is reduced > ICP token price appreciation
Software canisters can be written in any programing language that can be compiled to WebAssembly modules (e.g., Motoko, Rust) for deployment on the Internet Computer Blockchain.
Interoperability of Canisters
The canisters can decouple from their environment and interact with another canister or user to perform computation/execute the smart contract code. This interoperability feature of the canisters allows for the development of a wide range of services on Internet Computer.
Tracking the Canisters
Since all the data is publicly available for the Internet Computer Protocol blockchain, we can look at the currently deployed canisters (applications) using metrics websites like InternetComputer.org or Canlista.

With the external link, we can go to the application directly. As of 7/29/2021, there are around 2000 canisters currently deployed. This shows a significant amount of development activity.
The metrics canister is using the metrics canister to track the metrics canister 😎 pic.twitter.com/bcyJ9OR4dN
— Norton Wang ∞ (@floatfloatboat) July 9, 2021
Canister smart contracts running on the #InternetComputer surpassed 4,000🎉
— DFINITY Foundation (@dfinity) August 20, 2021
Canister smart contracts are computational units powered by cycles. An increase in Canister smart contracts speaks to the growth in developer activity on the network.
Live stats: https://t.co/e4FaOV7tnq pic.twitter.com/dZjQepRNjw
An Example of IC Canister Software
For example, OpenChat - One of my favorite projects on the Internet Computer is a messenger app similar to WhatsApp with a clean interface and over 10,000 active users (still in test mode, though). Its canister address is - 7e6iv-biaaa-aaaaf-aaada-cai

OpenChat runs 100% on-chain - Both Front end and Back end
"View URL " can directly take us to the application :

In the future, OpenChat will create one canister for each user & group chat. Therefore, an application can have multiple horizontally scaled canisters that can interact with each other using two-way messaging, making them secure, fast, and efficient.
Valuable Resources from DFINITY:
Start developing on the Internet Computer using canisters:

In-Depth technical details about Canisters:


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