VxWorks has a "flat binary file" format in which the initial 8 byte values are 45 53 54 46 42 49 4E 52 (ESTFBINR if interpreted as ASCII). I know very little about their content except:

  1. binwalk recognizes the magic bytes ESTFBINR and is able to find and extract and expand a zlib file from such flat binary files.
  2. The flat binary files that I have, all include an ASCII text copyright notice from Wind River.
  3. The "EST" in the signature is associated with a company called Embedded Support Tools that Wind River bought in about 2000.
  4. An old post to the u-boot mailing list stated that the format is associated with an old development tool from EST called VisionClick. I've confirmed this with a few google searches.

But additional searching has failed to yield an additional details about this format, so I'm hoping someone here may know more or be able to find additional information that I haven't turned up. (To my total lack of surprise, the AI chat bots have given me nothing else.)

  • When you're looking for history, check web.archive.org for press releases, EDGAR, and USENET archives. Specifically comp.os.vxworks which has this post: groups.google.com/g/comp.os.vxworks/c/i91b43VyBEQ/m/…. The names of people who worked on it during that time might also be helpful. Commented Dec 23, 2023 at 20:48
  • There's also this post which might be relevant as it mentions the signature you suggested: groups.google.com/g/comp.os.vxworks/c/AfMQ3lDVKM0/m/… Commented Dec 23, 2023 at 20:49
  • Sorry, what is your actual question? I can't seem to find it in the text...
    – Igor Skochinsky
    Commented Jan 3 at 16:38
  • I'm just looking for more information about what is inside a VxWorks flat binary file. The thread in comp.os.vxworks that Ali posted confirmed what I already knew about the initial 8 bytes, but the other details from that post don't appear to apply. There's no room to post any detail within the character limit here, and I'm out of time for now, but I will post again later about that thread, or edit my original post, when I have more time.
    – g1l1t1
    Commented Jan 4 at 19:15

1 Answer 1


It seems there is no defined structure besides the header - the rest of the file is basically raw binary, containing whatever data is necessary for the device to operate. I could find an example firmware here and the file simpy contains PPC code for the VxWorks bootloader with the compressed kernel. My quick RE notes:



load data from 0x20 to 0xFFF00100

compressed data starts at 62A8 (08 78 9C) with zlib stream at 62A9 (w=15)

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