Some enthusiasts have managed to create bootable "Tiny7" versions as small as 69MB , but these versions are often non-functional for daily tasks because they lack drivers, networking, and system files.
Technically, it is to compress a functional, full version of Windows 7 Ultimate 64-bit (which typically requires a 4.7GB ISO and 20GB of disk space ) down to just 10MB without removing almost every essential feature. Windows 7 Ultimate 64 Bit Highly Compressed 10mb
Instead of searching for a 10MB miracle, consider these more reliable methods: Some enthusiasts have managed to create bootable "Tiny7"