For users with slow internet connections, limited storage space, or older hardware, the idea of downloading a full 4-5 GB Windows ISO file is daunting. Enter the world of "highly compressed" operating systems: repackaged, slimmed-down versions of Windows that promise to cut download sizes by 50-80% while including "fixes" for common post-installation issues.
Go to "Adjust the appearance and performance of Windows" and select Adjust for best performance to reduce system load.
The most critical concern is the integrity of the source files. Because these operating systems are pre-modified, end-users have no easy way to verify that malicious software, such as keyloggers or backdoors, has not been injected into the system image. Furthermore, the aggressive removal of system components often breaks core dependencies. Users may find that they cannot install critical security updates, connect specific hardware devices due to missing driver frameworks, or run modern software that relies on the removed Windows features.
Downloading modified operating systems from third-party sites is highly risky windows 8.1 activation - Microsoft Q&A
Use or CertUtil to compare the provided MD5/SHA1. If none provided – abort.