first post on this site so go easy 
I am currently in the proccess of getting a new custom computer with these specs
•Gigabyte GA-970A-DS3 Motherboard
•AMD ATI Radeon HD 7870 2GB Graphics Card
•CIT Blue Vantage Gaming Case
•1 x 300MBs Wireless PCI Card WiFi Network Adaptor
•Xigmatek Apache CPU Cooler
•Xigmatek 600W PSU
•8GB Corsair Vengeance 1866MHz Gaming RAM
•3.8GHz AMD FX-6200 6-Core CPU
I am purchacing it with no hard drive, and wondering if I can take the HDD in my current PC which is a respectable 1TB with windows 7 home premium that came with the system. also pretty sure it is sata.
my old system : HP pavllion s5780uk, 4gb ram, nvidea geforce 405 (2 years old and not great when I got it, time for something that actually gives some oomph)
the only good thing about my current system is the drive as stated, would I be able to simply put in the current 1TB sata drive into the new custom PC and my win 7 OS and system Files would remain active? I have read that windows 7 will look for new drivers for the hardware but am not so sure, many places are saying that a clean install or serial numbers are required for the OS to run properly after being placed in new hardware, while others say it can just do it automatically.
the reason why I am not having the PC built with a HDD is because my budget is pretty much spent on aquiring the PC as it stands, and another hard disk is not needed if this current one can be placed with no hassle and the OS working with all my files intact.
have seen a thread before about transfering hard drives, but it was for vista and quite old hardware, looking for a fresh more up-to-date response
thank you in advance and awaiting response.

I am currently in the proccess of getting a new custom computer with these specs
•Gigabyte GA-970A-DS3 Motherboard
•AMD ATI Radeon HD 7870 2GB Graphics Card
•CIT Blue Vantage Gaming Case
•1 x 300MBs Wireless PCI Card WiFi Network Adaptor
•Xigmatek Apache CPU Cooler
•Xigmatek 600W PSU
•8GB Corsair Vengeance 1866MHz Gaming RAM
•3.8GHz AMD FX-6200 6-Core CPU
I am purchacing it with no hard drive, and wondering if I can take the HDD in my current PC which is a respectable 1TB with windows 7 home premium that came with the system. also pretty sure it is sata.
my old system : HP pavllion s5780uk, 4gb ram, nvidea geforce 405 (2 years old and not great when I got it, time for something that actually gives some oomph)
the only good thing about my current system is the drive as stated, would I be able to simply put in the current 1TB sata drive into the new custom PC and my win 7 OS and system Files would remain active? I have read that windows 7 will look for new drivers for the hardware but am not so sure, many places are saying that a clean install or serial numbers are required for the OS to run properly after being placed in new hardware, while others say it can just do it automatically.
the reason why I am not having the PC built with a HDD is because my budget is pretty much spent on aquiring the PC as it stands, and another hard disk is not needed if this current one can be placed with no hassle and the OS working with all my files intact.
have seen a thread before about transfering hard drives, but it was for vista and quite old hardware, looking for a fresh more up-to-date response
thank you in advance and awaiting response.