1. The compatibility of the hardware. Old laptops could be IDE or SATA. One really old machine used a ZIF/LIF connected HDD. Very strange. So first hurdle is what HDDs are these?
2. The OSes. Windows is locked to the laptop so when you move the drive, the OS usually BSODs and even if it boots will detect the hardware change and invalidate the license (OEM license issues are well done so I stop here.)
3. The factory recovery system has never worked across brands.
If speed is an issue, try a Linux on the Sony.
I have two old notebooks, one Sony extremely slow due to the Windows Vista and the other Asus with burnt motherboard but with Windows 7 (both bring partitions with the original Windows). I was thinking of swapping both HDD so I could run the Windows 7 on the Sony Vaio notebook. Would that work? I mean, apart from the drivers (I can search them online), would the built-in factory recovery reinstall the Windows 7 on the other notebook? Thanks