Recommend me a lightweight operating system for about 6 years old laptop with Intel Atom. 'nuff said I guess...

Google: Light Linux distros :p

@ScribeOfGoD Nah mate. Linux Mint is burning the CPU XD

And I think once it had an Ubuntu installed. It was horrific...

Can it run Win95!
Should be light weight enough.

@moodmister You should try http://www.slitaz.org/en/

@C0D4 Haven't tried that. Btw that laptop had 1gb Ram upgraded to 2 and pre-installed OS was WinXP Home Premium...

@Jilano Interesting

Debian of course, but don't install environment ( gnome) by default. Install either xface or my personal favorite : i3
Additionally you will need lightdm

It's mostly the window manager et all your environment that you want to be careful with. Distrib are not that much different, even arch use systemd. My Gentoo is a little better for the ram, but if your computer is really slow to compile software you may going to be angry x) worst case will be that you don't even have enough memory to compile a software.

So there is my idea. If you know linux or want to learn go for arch linux. If you don't go for manjaro.
About windows manager, there is a lot of really light but they need some work :i3, bspwm, awesome, dwm, xmonad...
If you need something more 'user friendly', try manjaro with xfce. I don't remember how much it will use, but it wasn't that much and you get a 'window' gui.

Theres a puppy linux, or something like that, not exactly sure of the name.

Use gentoo

Got Lubuntu on my old laptop and installed i3wm,ultra minimal,at idle most of the time sits on 300-500mb Ram.

@zmzmuazzam98 not sure if I will recommand LUbuntu then. Gentoo/i3 : 250mb with already some apps and scripts running.
If I check htop with the usb installer:
Manjaro/xfce : 495mb
Manjaro/i3 : 480mb (wtf, seems like there is a lot of thing to delete)
Manjaro /deepin: 820mb

Well if you have some time a manual install will allow you to save some ram, using only what you need to.

Microsoft Windows 10

@shaji you forgot the best part : 1.5Gb :D

Elementary os

@JonnyCodewalker systemd not mandatory if I remember, take some ++ :p but there is no installer with a window manager no?

Maybe Linux Lite or Arch Linux (depending on the way you install)

The DE will have a huge impact on the performance

You can check out any distro with XFCE or install Arch with XFCE.

If you don't want the trouble of installing (which is practically zero after you do it a few times), install Manjaro XFCE. It'll use around 400 MB RAM and it'll be light on the CPU as well.

Lubuntu (Ubuntu running LMDE) is good as well. LMDE on Arch would be better.

Avoid bloated distros like Ubuntu - they'll crawl. Maybe even worse.

Puppy Linux is very light but not a lot of options for software etc.

Actually, have any of you heard about Remix OS? Didn't find any reviews on it. What're your opinions?

@JonnyCodewalker I honestly don't know