The Requirements for Stronghold HD are:

Operating System: Windows 95, 98, ME, 2000, XP, Vista, 8, 10
CPU: 200 MHz (550+ preferred)
RAM: 64 Mb
HDD: 750Mb
Video: 4Mb DirectX 7.0 Compatible
Sound: DirectX 7.0 Compatible
CD-ROM: 8x Speed
Modem: 56k (For Internet Play)

Note: Stronghold 1 will work on Windows XP and Windows Vista when run as an Administrator.