If you have exported Gerber files in the last decade, you have probably met both names — sometimes as alternatives in the same dialog, sometimes used as if they were rivals. They are not rivals. RS-274X is the classic Gerber format: a complete description of one board layer as an image, drawn with apertures. Gerber X2 is that same format with an attribute system added — structured extra information carried inside the file, saying what the layer is for and what the objects in it belong to. X2 did not replace the image; it labelled it. This article explains what the attributes add, what stays identical, and what it means for viewing files in Gerbv. For the broader format picture, see what a Gerber file is and the Gerber viewer hub. The tools that read these files are compared in our roundup of the best free Gerber viewers.
RS-274X: the image, complete in itself
An RS-274X file is self-contained in a way its predecessor was not: the aperture definitions, units and format settings travel inside the file, and the drawing commands that follow describe the layer’s copper, mask, legend or paste pattern exactly. (The older RS-274D needed a separate aperture file, which is why Gerbv — an RS-274X viewer — cannot open it.) What an RS-274X file does not contain is intent. It knows a shape is a filled rectangle of a certain size at a certain place; it does not say whether that rectangle is a pad, a test point or a logo. Humans infer the layer’s role from the filename; machines historically did the same, with the filename chaos that implies.
What X2 adds: attributes
Gerber X2 keeps the RS-274X image exactly as it is and adds attributes — named pieces of metadata attached at three useful levels. File attributes describe the file itself, most importantly its function: this is the top copper layer, this is the solder mask, this is the board outline. Aperture attributes connect drawn shapes to their role, such as being pads for a component. Object attributes go furthest, attaching part and net information to the objects drawn — this flash belongs to this component pin, on this net. Nothing about the picture changes; what changes is that the picture arrives with a caption written in a standard vocabulary, instead of a filename in someone’s personal shorthand.
Why attributes matter in practice
The classic failure attributes prevent is the misidentified layer: a fab importing a set where a file’s role was guessed from its name, guessed wrong, and built. With X2 file-function attributes, software can identify layers by content, flag a missing layer by role rather than by absence from a list, and refuse ambiguity instead of guessing silently. Net and part attributes push further — they let downstream tools reason about connectivity and components rather than treating the board as pure geometry. Even if your own routine is visual, you benefit every time a fab’s importer stops misreading your set. When you receive files, the header of an X2 file tells you what the sender intended each layer to be, which is a far better starting point than deciphering suffixes — although suffixes still matter, as Gerber file extensions explained covers.
Compatibility: X2 files are still Gerber files
Because the image layer of the format is unchanged, an X2 file is still an RS-274X file with extra information embedded in it. Viewers read the drawing as they always have. Gerbv views RS-274X files, and an X2 file’s image renders in Gerbv like any other layer — you can stack it, measure it and export views of it from the download page build. What a plain viewer does not do is exploit the attribute layer: Gerbv will show you the top copper, but identifying it as top copper remains your job, done with the filename and context as the attributes sit unused. That is a viewing limitation to know about, not a rendering problem — the geometry you are checking is complete.
Which should you export?
If your CAD tool offers X2, exporting with attributes is the better default for sending work to a fab: the same image, plus machine-readable intent that reduces misidentification at import. Keep your filenames sensible anyway — humans, archives and checklists still run on names, and attributes complement filenames rather than excusing cryptic ones. If your tool offers only classic RS-274X, your files remain perfectly manufacturable; most of the world’s boards are described exactly that way. The format question to never get wrong is the older one: RS-274X (with or without X2 attributes) is the living standard, and RS-274D is the legacy format modern viewers, Gerbv included, do not support.
Frequently asked questions
Is Gerber X2 a different file format from RS-274X?
Not in its image. X2 is RS-274X with an attribute system added: the layer is drawn exactly as before, and attributes inside the file add the layer’s function plus part and net information. An X2 file is still a Gerber file.
Can Gerbv open Gerber X2 files?
Yes — the RS-274X image in an X2 file renders in Gerbv like any other Gerber layer, so you can stack, measure and export it. Gerbv does not itself use the attribute data, so identifying each layer’s role remains a filename-and-context job for the viewer.
Should I export X2 or plain RS-274X?
If your CAD tool offers X2 attributes, use them when sending files to a fab: the image is identical and the embedded layer-function information reduces the chance of a layer being misidentified. Plain RS-274X remains fully manufacturable everywhere.