OS/2 Boot Logo

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File Format
Name OS/2 Boot Logo
Extension(s) (none), .lgo
Released 1994

OS/2 Boot Logo is a compressed raster graphics format used for the logo shown when OS/2 Warp operating systems boot. Images are 640×400 (Warp 3), or 640×480 (Warp 4), with 16 colors.

The file used by the operating system is named "OS2LOGO", with no filename extension. Inactive logo files are conventionally given the extension .lgo.

No public format specifications are known.

Format details

This is an incomplete, and possibly inaccurate, description of the format.

The image data is separated into four bit-planes, which are compressed and stored separately.

The file begins with a 32-byte header of 8 four-byte integers: the file offset of plane 0, the length of plane 0, the offset of plane 1, the length of plane 1, and so on.

A compressed plane of data seems to consist of a sequence of elements, each of which begins with an opcode byte, followed by a variable number of data bytes.

GBM says that it uses EXEPACK compression, but this is unconfirmed, and there are several different versions of EXEPACK.

This much is known about an element:

Opcode (N) Following bytes Description
0 0 End-of-data marker
0 count, val RLE: Emit count bytes of value val.
N mod 4 = 0 ... Uncompressed: Emit the next N/4 bytes literally.
other ... Unknown; apparently one or more other (LZ?) compression methods

This is the VGA palette used by GBM:



  • PMView Pro
  • PrepLogo (OS/2 software; write-only)
  • MAKELOGO - A utility on the IBM OS/2 Developer Connection CDs, which can create a logo file from raw bitmap files
  • GBM → GBMLOGO (write-only; requires MAKELOGO)
  • BMP2LOGO.ZIP (OS/2 software; write-only; requires MAKELOGO)

Sample files

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