He devised a systemof storage for all the slips in shelves of pigeonholes that lined the walls of theScriptorium.
The scriptorium for the OED relied on shelves of pigeonholes into which the slips could be sorted and stored.
There are photos of Murray with these pigeonholes stuffed behind him. Dig one of these up.
This pigeonhole practice is in marked difference to other projects like the TLL which relied on boxes on shelves.