Third-party creators often use experimental tools like KGB Archiver or 7-Zip with extreme settings (LZMA2/PPMd). While these can technically reduce file sizes further, decompressing them can take hours or even days and often results in corrupted data. The Major Risks
To achieve extreme compression, creators often "strip" the OS of essential drivers, system files, and features. This can lead to frequent crashes, the "BOOTMGR is compressed" error, or an inability to boot the system at all. Windows 7 all versions highly compressed
Microsoft uses ESD files because they use "solid compression," where files are streamed together as one large blob for better efficiency. This typically reduces a 5GB installer to roughly 3.5GB. Third-party creators often use experimental tools like KGB
Look for archived versions of official Microsoft installers from reputable sites like TechBench by WZT , which fetch links directly from Microsoft servers. This can lead to frequent crashes, the "BOOTMGR