Mór
I am not running other people's games on this machine.
Well you said you have gaming computer. Typically that means its for playing games. If you are not, then no worries. Just be safe when browsing Internet. This is relevant even without spectre/meltdown, because who knows how many exploits are there which are not yet discovered by security reasearchers.
Sure, meltdown is easier to exploit, but Spectre is harder. But that's still should be scary. Security doesn't work like that. Even if there is slightest change to exploit it, the attackers will do that. Even if it is super hard - they'll find the way. And currently there is no easy way to avoid Spectre.
But is it necessary for the computer to have SSD or is HDD fine? What's the difference?
HDD is fine. SSD is better. You can do everything in HH fine with just a HDD. Afaik Casey is still using HDD - since beginning of HH.
SSDs typically are 4-5x faster than HDD for large file reads/writes. And crazy faster for small file reads/writes due to fast they don't need to seek. NVMe SSDs can be even 10-20x faster than regular HDDs. If you can afford, get smaller SSD for your OS and important software. And leave HDD for big data storage. Putting SSD in older computer/laptop gives significant boost in perceived performance.