Coretime for beginners Part 1: Coretime vs Web Server (aka What is This Coretime Thing Anyway?)
The goal of this series is to make Coretime easier to understand. I imagine the reader is a web2 dev, or a web3 enthusiast or someone tech savvy who is keen to learn. I will make parallels with web servers/cloud, and not everything is 100% technically accurate, some things were simplified to make this vast topic easier to absorb.
Definitions
Relay chain
The central blockchain of the Polkadot network that coordinates security, consensus, and cross-chain communication between all parachains. It focuses on validating and finalizing parachain blocks to keep the entire network secure and synchronized.
Parachain/Rollup
An independent blockchain that runs in parallel to others on the Polkadot network and connects to the relay chain for shared security and interoperability.
TLDR: Coretime on Polkadot is like renting computing time on a server. Just like a web server gives your app a “place” to run, renting a core gives your parachain a place to execute logic on the relay chain. You can buy coretime up front (during the sale), or on-demand (on -demand cores are processing requests in real time without reservation), and your parachain’s performance can be improved by more coretime (but not necessarily).
Let’s unpack this.
Coretime on Polkadot is like renting computing time on a server.
Basically “coretime” is time on a core (surprise surprise) on this marvellous thing called Ubiquitous Computer aka Polkadot. In web2, you might rent a server to run your app and perform necessary computations/execution. In Polkadot, you rent coretime (on a core) to let your parachain execute its logic.
Kind of like spinning up a server to host a cute little blog where you share grandma’s favourite cookie recipes — maybe even with a small e-shop selling cookies engraved with Bitcoin block hashes. But if you decide to take it further and launch GRANNY blockchain, complete with its own tokens and smart contract-powered oven timers, then you’ll need coretime.
| Web Server | Polkadot Coretime |
|---|---|
| A web server handles requests from clients (like browsers) and processes them using CPU/memory resources. | Cores validate and process blocks for parachains/rollups in the Polkadot space. |
| Users send requests and receive (packets) web pages with information back. | Users make transactions and those transactions are added to the block, which then is validated, making their transactions final. |
| You can rent or provision server time (e.g., virtual CPU on AWS) to run your applications. | You can buy coretime to run your parachain on Polkadot’s relay chain. |
Just like a web server gives your app a place to run, renting a core gives your parachain a “place” to execute logic on the relay chain.
Think of coretime as CPU time credits —cores are not real hardware, but reserving one gives you permission to run things on the Polkadot relay chain. By owning coretime you are allowed to use some of Polkadot computing power.
| Web Server | Polkadot Coretime |
|---|---|
| You buy a VPS or cloud instance with defined compute capacity. | You buy coretime chunks in bulk, each representing a unit of processing time on the relay chain. To be precise each is 80 blocks of relay chain time. |
You can buy it up front (during the sale), or on-demand (on demand cores are processing requests in real time without reservation).
Coretime can be purchased during a recurring sale period that runs every 28 days (at the time of writing — this may change in the future). The price starts high and gradually decreases throughout the sale, following a descending price curve. More about the sale in the coming articles.
You can either own a full core, giving you predictable compute power over time, or you can use on-demand cores, which let you tap into shared computing power only when needed — a kind of pay-per-use model. On-demand coretime is a bit like serverless functions in web2: they spin up to handle a request and go idle when not in use.
| Web Server | Polkadot Coretime |
|---|---|
| Pay a monthly subscription to cloud providers like AWS or DigitalOcean. | Pay DOT/KSM tokens for coretime (bought from the sale process or a 3d party marketplace). Turn on auto-renew for no-stress periodic renewals of your cores. |
| Create serverless functions instead of spining up a whole server. | Use on demand coretime to only execute the logic that you need at the time when you need it. |
…and your parachain’s performance can be improved by more coretime (but not necessarily)
This means that depending on what type of business you are running you might need more processing power, just like in web2 world.
If you run a big multiplayer game you will probably not do it from your favourite Pentium II computer in your garage. You would rent a few hot servers from a nearby server farm. If you are running a multiplayer game using blockchain for payments, you might need more coretime in order to be able to satisfy the demand for a lot a lot (and a lot) of real time transactions. It is simple, you just buy more cores. However of course that is not the only way to improve performance of your chain. There are many other aspects here, which is out of scope of this article.
| Web Server | Polkadot Coretime |
|---|---|
| Runinng a big multiplayer game would require a lot of CPU power (and graphics). You might have serveral servers running at the same time. | Running a big multiplayer game with blockchain transactions would require purchase of more cores in order to process your transactions more efficiently. |
What is this core thing anyway?
Naturally after the above explanation you imagine a core being something like a CPU and then you see server racks stored in a cool looking server room, which is all lit up with green.
In reality a core is a set of validators. Validators are the heart of any blockchain, they are blockchain bees tirelessly working for the benefit of the majority. Validators validate blocks (a bunch of transactions in a box), and by doing so they make those blocks final, and allow them to be added to the source of truth. The source of truth is the ledger everyone refers to, when they check transactions and balances. In case you want to dive deep into how validators actually perform their duties on Polkadot, please refer to The Path of a Parachain Block.
However when you think about the cores in the future feel free to think about them as CPUs, that might be easier. Or you know what, think whatever you like, since now you know the truth about Coretime and you are free to make that decision.
Conclusion
I hope this was informative. I am planning to write more articles for this series which will explain things like: The Sale, Renewals, Pricing, and any other things that people are interested in.
Thank you for reading 
Resources
Here are some cool and very complex things to read/watch if you feel like nerding out to the max.