What algorithm did Monero use before RandomX?
Monero used CryptoNight before RandomX. More precisely, its last mining algorithm before the switch was CryptoNight-R, a version of CryptoNight that RandomX replaced on November 30, 2019.
CryptoNight was the original starting point
When Monero launched on April 18, 2014, it used CryptoNight as its proof-of-work algorithm. That means CryptoNight supplied the computing task miners performed to compete for the right to add a block of transactions to the network.
Monero began as a fork of Bytecoin—a project built from Bytecoin’s code—and inherited its CryptoNote foundation. Two similar names can make this history confusing:
- CryptoNote was the broader design behind the currency, including parts of its transaction and privacy system.
- CryptoNight was the mining algorithm used within that design.
So, if you are looking for the name of Monero’s old mining algorithm, CryptoNight is the answer. CryptoNote is related, but it is not the name of that computing task.
There were several CryptoNight versions
Monero did not use one unchanged version of CryptoNight all the way up to RandomX. It changed the algorithm several times, largely to resist specialized mining machines.
The main sequence was:
- Original CryptoNight: Used from Monero’s launch in 2014.
- CryptoNight variant 1: Introduced in April 2018. You may also see it called CryptoNightV7.
- CryptoNight variant 2: Introduced in October 2018. Often called CryptoNightV8.
- CryptoNight-R: Introduced in March 2019. This was the final CryptoNight version Monero used.
- RandomX: Activated on November 30, 2019.
Those alternative names matter when you read older mining guides. A guide that says “CryptoNight” may describe the general family, while a miner’s settings may name one specific version. The versions were not interchangeable: mining software had to follow the algorithm the network was using at the time.
Why Monero moved away from CryptoNight
CryptoNight was designed to make mining depend on fast access to memory, not just raw calculation speed. The aim was to reduce the advantage of ASICs—specialized chips built to perform one particular task, such as mining a specific algorithm.
Despite that design, CryptoNight ASICs appeared. Monero responded by changing CryptoNight, making existing specialized machines unsuitable for its updated mining rules.
RandomX took a different approach. It makes miners execute varied sequences of instructions that suit a general-purpose CPU, the main processor in your computer. Its design favors CPUs rather than dedicated mining chips.
That does not mean every CPU earns a profit, or that specialized hardware is impossible. It describes the design goal, not a guarantee of earnings or permanent resistance to ASICs.
The bottom line
CryptoNight was Monero’s pre-RandomX algorithm family, and CryptoNight-R was its immediate predecessor. If you find an old Monero mining tutorial mentioning CryptoNight, treat its setup instructions as historical. Today, software mining Monero directly must support RandomX; an old CryptoNight miner cannot simply keep mining the current Monero network.
