Pick any molecule in the grid. A Sparsr processor running in your browser compares it against all 4,096 in the library and shows you the closest.
Why it takes so few instructions
The obvious way to screen a library is one comparison per molecule: 4,096 of them. This does it in about twenty instructions.
The trick is how the library is stored. A Sparsr register is 4,096 bits wide, and the library is held sideways — one register holds a single fingerprint bit for all 4,096 molecules at once. So the machine works through the query's bits rather than through the library's molecules, and every instruction touches the entire library.
That is the whole idea of the processor, on a job people actually run.
What similarity means here
Each molecule is reduced to 1,024 bits recording which small substructures it contains — an ECFP4 fingerprint. Two molecules are compared by how much their bit patterns overlap, which is the Tanimoto similarity: 1.000 is the molecule itself, and the numbers under the grid fall away from there.
Chemists use this to find compounds that might behave alike. It measures the shape of a molecule's substructures, not what it does in a body — two similar-looking molecules can behave completely differently, and the measure makes no claim otherwise.
Where the molecules come from
The first 4,096 compounds of the US National Cancer Institute's Open Database, as bundled with RDKit and distributed under BSD-3-Clause.
The fingerprints were computed once by RDKit and ship with the page, because computing one in a browser is not possible — that is RDKit's job and it is Python and C++. The structures are drawn in your browser from SMILES strings by SmilesDrawer, which is why this page is a few hundred kilobytes of chemistry rather than tens of megabytes of pictures.
What this does not tell you
Nothing about speed. The processor here is a software model running in your browser, so how long a screen takes is a property of your laptop rather than of Sparsr. The instruction counts are exact; there is deliberately no timing figure beside them.