---
title: "Nominate the two sides · DuplicateDuster"
description: "From pointing it at a folder to a list of exact copies."
url: "https://royalsoftworks.com/products/duplicate-duster/how-it-works/nominate/"
source: "https://royalsoftworks.com"
format: "markdown"
note: "Markdown rendering of the HTML page at `url`. Same content, same canonical URL."
---

How it works · 1 of 3

# Nominate the two sides.

From pointing it at a folder to a list of exact copies.

1. 01

   ## Nominate the two sides

   Source folders hold what you're keeping. Target folders are the ones being cleaned. Either side can be one folder, several, or a single file, and the scan is recursive from each root you pick.
2. 02

   ## Narrow it, if you want

   Optional filters: a minimum or maximum file size, an include or exclude list of extensions, skip dot-files, skip system folders. Zero-byte files are always excluded — they match each other by definition and removing them frees nothing.
3. 03

   ## Both sides are walked and indexed by size

   Every file in scope is listed and grouped by exact byte size. Nothing is read or modified in this pass. Permission errors are recorded as warnings and the walk carries on — one unreadable folder must never end a scan.
4. 04

   ## Only plausible candidates get hashed

   A file whose exact size appears nowhere on the other side cannot be a duplicate of anything there, so it is never opened. On a typical drive that eliminates the overwhelming majority of the bytes before hashing starts.
5. 05

   ## Hash in parallel, SHA-256

   The survivors are hashed across a worker pool — about three quarters of your cores, capped at sixteen — handed out in batches so no thread sits idle behind a large file. For a trivial amount of work the pool isn't started at all, because spinning up threads would cost more than it saves.
6. 06

   ## Group files, then whole folders

   Identical hashes are grouped as confirmed byte-for-byte duplicates. The same data is then walked upward: any target folder whose entire recursive contents exist in the source is reported as a folder match — the topmost one only, so a match doesn't bury you in its own subfolders.
7. 07

   ## Review everything

   Each group shows the source copy with a keep badge and no checkbox, and the target copies with full paths, sizes and dates. Search the results, expand or collapse everything, and watch the reclaimable total update as you select.
8. 08

   ## Reclaim, four ways

   Recycle bin by default, or permanent delete, a three-pass secure erase, or replacing the copy with a hard link to the original. A confirmation names the file count, the total size and, in one sentence, exactly what is about to happen to those files.
9. 09

   ## Clean up after itself

   Failures are collected and reported per file rather than aborting the batch, protected system paths are refused whatever was selected, and directories the cleanup left genuinely empty are removed, deepest first.

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