Some files refuse to open in Gerbv for a reason that has nothing to do with your computer, your installation, or the file’s condition. They refuse because they belong to an older generation of the Gerber format — RS-274D — and Gerbv’s support is explicit on this point: it views RS-274X files, and RS-274D files are not supported. That sentence, from the project’s own documentation, settles a class of troubleshooting that otherwise eats hours. This guide explains how to tell whether your files are RS-274D, why the older format cannot simply be read as if it were the newer one, and the two practical routes to viewable data: re-exporting as RS-274X from the CAD tool, which is the right answer whenever it is available, and converting the old files where re-export is impossible. Background on the formats themselves is in what a Gerber file is, and current Gerbv builds are on the download page.
How to recognise RS-274D data
RS-274D, sometimes called Standard Gerber, dates from an era when the file held only movement and exposure commands. Two fingerprints give it away. The first is company: an RS-274D file travels with a separate aperture file — a wheel or aperture list, often with a name suggesting apertures, that defines what each aperture code (D-code) in the drawing actually means: its shape and size. The second fingerprint is absence: the RS-274D file itself contains no embedded parameter block declaring units, format and apertures, because that information lives outside it. RS-274X — Extended Gerber — folded all of that into the file itself, which is why an X file opens self-contained anywhere, and why a D file without its aperture companion is not a complete description of a board at all. If your archive contains an aperture list alongside sparse drawing files, or the files came from a very old CAD system or an archive of an old design, you are almost certainly holding RS-274D.
Why Gerbv cannot just read it anyway
This is not a missing-codec problem. An RS-274D command says, in effect, draw with aperture D12 — and D12 means whatever the external aperture file says. Without that file the geometry is undefined: the same command could be a fine line or a large pad. A viewer that guessed would produce a board-shaped fiction, worse than no picture at all. RS-274X removed the ambiguity by embedding apertures, units and format in the file. Treat a refusal here as a format verdict, not a malfunction. If the same set also fails the basic checks in Gerber files that will not open, resolve the format question first, because it sits underneath all the others.
Route 1: Re-export as RS-274X from the CAD tool (preferred)
If the design still exists in any reasonably current CAD tool, re-export solves everything at once. Open the design, choose the Gerber export, and select RS-274X — in most modern tools this is the default Gerber output and may simply be labelled Extended Gerber or X — then export the full layer set and the Excellon drill data in one pass, with one origin and one unit system, exactly as you would for a new board. The result is a modern, self-describing set that Gerbv opens directly, following how to open Gerber files. Re-export has a second advantage over conversion: the data comes from the design itself, not from an interpretation of an old drawing file, so nothing depends on reconstructing an aperture wheel correctly. Whenever the source design is reachable, this route is not merely preferable — it makes the conversion route unnecessary.
Route 2: Convert the RS-274D files
Sometimes the design is gone and only the old fabrication files survive — an archive, a former contractor’s delivery, a board that must be reproduced or studied as-is. Then conversion is the task: an RS-274D-to-RS-274X translation, in which the external aperture definitions are embedded into the file and the drawing commands are rewritten in the extended format. Two cautions govern this route. First, conversion is only as good as the aperture file: if the wheel file is missing or belongs to a different revision, the converted geometry will be wrong in ways that look plausible, so verify the converted set in Gerbv with unusual care — measure known features, compare against any surviving drawing or physical board, and treat the first view as a hypothesis. Second, use a conversion path you can inspect: Gerbv itself documents export to RS-274X among its export formats for data it can read, and CAD tools that still import RS-274D can typically re-export it as X, which is route 1 applied to the files rather than the design. What you should not do is send unconverted — or unverified converted — legacy data to a board house on the assumption that their toolchain will sort it out silently.
What about the drill files from the same era?
Old sets pair RS-274D artwork with drill data of a similar vintage. Excellon drill viewing is supported in Gerbv, and drill files from older workflows often load — but check them with the full discipline of viewing Excellon drill files: units, coordinate format and zero suppression were even less standardised in older exports, and an era-correct drill file can still be misread by modern assumptions. Overlay the drills on the converted copper and require centred holes everywhere before believing either file.
Prevention and archiving advice
If you maintain designs with any future, export a fresh RS-274X set now, while the CAD source is at hand, and archive it alongside the design files. Legacy formats do not become more supported with time. When you receive an old set from someone else, ask early whether it is D or X — that one question, asked before the troubleshooting starts, is the whole lesson of this page in miniature.
Frequently asked questions
How do I know my files are RS-274D and not RS-274X?
Look for a separate aperture or wheel file travelling with the drawing files, and for the absence of an embedded parameter block in the Gerber files themselves. RS-274X carries apertures, units and format inside the file; RS-274D keeps apertures outside it.
Can I make Gerbv open RS-274D with a setting or plugin?
No. Gerbv’s documented support is RS-274X only, and RS-274D is explicitly not supported, because the drawing commands are undefined without the external aperture file. Re-export or convert the data to RS-274X instead.
Is conversion as good as re-exporting from the design?
Re-export is better, because the data comes from the design itself. Conversion depends entirely on having the correct aperture file for that revision, so verify a converted set in Gerbv by measuring known features before trusting or sending it.