Free webp to jpg
EN
Image MIME Reference
ICO

Windows Icon (Legacy MIME)

image/x-icon
VS

X Bitmap (Legacy MIME Alias)

image/x-xbm
XBM

A complete technical comparison of Windows Icon (Legacy MIME) and X Bitmap (Legacy MIME Alias) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

ICO wins on browser support

Feature Support

Feature ICO XBM
Transparency (Alpha) Yes Yes
Animation Support ✕ No ✕ No
Progressive Loading ✕ No ✕ No
HDR Support ✕ No ✕ No
EXIF Metadata ✕ No ✕ No
ICC Color Profile ✕ No ✕ No
Windows Icon (Legacy MIME)
image/x-icon
Extension
.ico
Container ICO Directory Structure
Compression Uncompressed (DIB/BMP) / Deflate (Embedded PNG)
Algorithm
NoneDeflate (via PNG)
Color Depth 1-bit, 4-bit, 8-bit, 24-bit (True Color), 32-bit (RGBA)
Developed by Microsoft Corporation
Released 1985
Magic Bytes
00 00 01 00
Full ICO reference →
X Bitmap (Legacy MIME Alias)
image/x-xbm
Extension
.xbm
Container C Source Code Header (.h)
Compression Uncompressed (Source Code)
Algorithm
None
Color Depth 1-bit (Monochrome)
Developed by MIT / X Consortium (X Window System)
Released 1988
Magic Bytes
23 64 65 66 69 6e 65 (ASCII '#define')
Full XBM reference →

Browser Support Comparison

Browser ICO XBM
Chrome Chrome
✓ 1
 ✕
Firefox Firefox
✓ 1
 ✕
Safari Safari
✓ 1
 ✕
Edge Edge
✓ 12
 ✕
IE IE (Legacy)
✓
✓
ICO

ICO Strengths

  • Universally supported by every web browser in existence for website favicons
  • Packs multiple resolutions into a single file, eliminating the need to serve different files for the taskbar vs. the desktop
  • Modern support for embedded PNGs (since Windows Vista) allows for excellent 32-bit transparency (alpha channels) and drastically reduced file sizes
Limitations
  • Internal file structure is convoluted due to decades of legacy cruft, such as the requirement for BMP data to lack a standard file header but double the height property for an archaic XOR/AND mask
  • Larger file size compared to a single optimized PNG or SVG, as it literally stores the same image multiple times at different scales
  • The MIME type landscape is highly fragmented (x-icon vs. vnd.microsoft.icon), causing occasional caching or strict-MIME validation errors on restrictive servers
XBM

XBM Strengths

  • Can be compiled directly into C or C++ source code without needing an external file loader or binary asset manager
  • Human-readable structure allows developers to inspect, edit, or hand-craft tiny icons directly within a text editor
  • Extremely predictable and lightweight for 1-bit hardware displays and embedded systems
Limitations
  • Strictly limited to 1-bit monochrome (black and white) graphics with no gray or color support
  • Text-based C syntax creates massive file bloat compared to binary 1-bit formats like PBM
  • Completely deprecated in modern web browsers and desktop GUI frameworks

When to choose which format

ICO
Use ICO when…
  • Website Favicons (favicon.ico)
  • Windows Application Executable Icons (.exe)
  • Desktop Shortcut Icons
XBM
Use XBM when…
  • X Window System (X11) Cursors and Icons
  • Embedded C/C++ Firmware UI Assets
  • Early 1990s Unix Web Graphics

More comparisons

ICO vs ACES → XBM vs ACES → ICO vs APNG → XBM vs APNG → ICO vs AVCI → XBM vs AVCI → ICO vs AVCS → XBM vs AVCS → ICO vs AVIF → XBM vs AVIF → All comparisons →
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