The DAG-based memory-hard PoW that defined the GPU mining era.
Ethash (and its variant Etchash) is the proof-of-work algorithm that powered Ethereum from 2015 until the Merge in September 2022. Today it lives on through Ethereum Classic, EthereumPoW, and a small set of forks. Ethash is memory-hard — it requires a large DAG (directed acyclic graph) of pseudo-random data that grows with block height, currently exceeding 6 GB. This memory requirement was the central design choice that made Ethash GPU-favorable for nearly a decade.
Each Ethash hash requires reading 128 bytes from a large pseudo-random DAG stored in GPU memory. The DAG itself is regenerated every 'epoch' (~5 days on ETC). Because the lookup is memory-bandwidth-bound rather than compute-bound, GPUs with high VRAM bandwidth (GDDR6X, HBM2) significantly outperform compute-heavy chips. ASICs do exist — Antminer E9 Pro, Linzhi Phoenix — but their efficiency margin over high-end GPUs is narrow (typically 2-3× vs the 100×+ seen on SHA-256).
Pre-Merge, Ethash was the most popular GPU mining algorithm by hash rate. Ethereum Classic absorbed a fraction of that hash rate after September 2022 and remains the largest active Ethash market. Modern GPUs (RTX 3080/3090/4090, AMD RX 6800+) dominate; older 4-6 GB cards can no longer hold the full DAG and have aged out. Etchash, the ETC variant, uses a slightly different DAG that allows older cards a longer useful life.
Post-Merge Ethash profitability has been compressed. ETC absorbed most active hash rate but its market cap is a fraction of pre-Merge Ethereum's. The RTX 4090 on Etchash at $0.06/kWh yields roughly break-even-plus in 2026; ASICs like the E9 Pro have a slight edge but at significantly higher upfront cost. The DAG-size growth ages out older cards every 6-12 months.
What is the Ethash algorithm?
Ethash is a memory-hard proof-of-work algorithm that requires reading from a large DAG (currently 6+ GB) stored in GPU memory. It was used by Ethereum 2015-2022 and is still used by Ethereum Classic via the Etchash variant.
Which coins use Ethash today?
The largest is Ethereum Classic (ETC) using Etchash. Smaller chains include EthereumPoW (ETHW), Callisto, and EthereumFair.
Ethash vs Etchash — what's the difference?
Etchash is ETC's variant. It uses a slightly modified DAG generation that allows 4 GB GPUs a longer useful mining life than they'd get on full Ethash.
Is Ethash ASIC-mineable?
Yes, but the GPU-to-ASIC efficiency gap is narrow (2-3×) compared to algorithms like SHA-256. ASIC mining Ethash is viable but high-end GPUs remain competitive.