The SSDs you mention, Samsung 830, 840 or 840 Pro, have encryption hardware. I believe that you should use it for best performance. Be aware that there are many articles criticising early versions of most consumer-based encrypting drives firmware. Security Boulevard has another article titled: "SSD Encryption from Crucial and Samsung is not secure Exposes Data". There are ways to avoid some of those problems, see my other answer on Crypto.SE.
The hardware is something you're paid for, since enabling encryption invites no penalty compared to software encryption it makes to use it or buy a lower priced SSD.
You can enable encryption and set new passwords using a bootable USB drive with the necessary software on it. An example is offered on Puget Systems webpage: "Introduction to Self-Encrypting Drives (SED)" which offers a bootable DVD image including hdparm, another program that you can use is sedutil which is available for Linux and Windows. See also VxLabs article: "Use the hardware-based full disk encryption of your TCG Opal SSD with msed and the update linked at the bottom of the article. This article specifically mentions the Samsung 840 Pro and hdparm.
You can improve your security by using software encryption in addition to the hardware encryption on your drives, this is useful because hardware encrypted drives are only secure when powered off. An unlocked hardware encrypted drive in a powered system (such as a laptop in sleep mode) isn't secured.
Since you are using "a pretty old Core2 Duo P8700 at 2.53 GHz, without AES-NI" you should consider software other than AES 256.
Google's latest algorithm is Adiantum is being added to the Linux kernel v5.0 and Android common kernels v4.9 and up. Where hardware support for AES exists, AES is faster than Adiantum. For low end processors Adiantum (fast hash (NH + Poly1305) and a fast stream cipher (XChaCha12)) on an ARM Cortex-A7 processor is over five times faster than AES-256-XTS. There is a reference implementation on GitHub and paper titled: "Adiantum: length-preserving encryption for entry-level processors". Note: Adiantum is not as secure as AES, but AES is quite slow on low end processors; unusably so.
Check out the various webpages about the Caesar (Competition for Authenticated Encryption: Security, Applicability, and Robustness) entries, some are faster than AES and purported to offer security improvements over AES:
You might be interested in the GitHub webpage: "MORUS-1280-256 Authenticated Cipher".
Best Answer
To see the device description for the controller (assuming an internal (PCI) controller), which usually contains SATA for SATA controllers:
If you want to type less, just browsing the output of
lspciis likely to give you the answer in a laptop (many desktop have both kinds of interfaces so you'd have to look up the drive you're interested in).If that doesn't give you the answer, to see what driver is providing
sda(you can then look up whether that driver is for a PATA or SATA controller):