My New Laptop Have Single Channel With A 1 Slot 8gb

Is it ok to have a laptop that has 4GB of RAM on one slot and 12GB to another slot?

There is no way you can put 12 Gb in one of the slots, because there are no commercially available 12 Gb RAM sticks. Even if that is memory directly soldered to the motherboard, it is very unlikely to have such amount in only one channel. If you’re not sure what you have currently installed, download the CPU-Z app and inspect the reported content of your RAM slots. One or both slots might not be actual slots with removable sticks though, and just soldered memory instead. To tell the difference you must pop the laptop open and do a visual recognition or search for memory specifications in the model manual.If your laptop has 2 real slots, then try to get a matched pair of RAM sticks of the same or better timing specifications. If you mix timing specs between slots, BIOS should default to the speed of the slowest in order to get stable performance, since they all are run with the same specs. If you don’t want to spend money and already have a slower RAM stick around, you should consider if installing it is convenient. If you have less than 8 Gb or only one slot populated, go for it. Even at a reduced timing, having 8 or more gigabytes of memory available will likely speed up some tasks that may be slowed down by occasional file swapping.If one of the sticks has a different capacity than the other, the smaller one will define how much RAM will get the benefit of double channel. For example, if you have one 2 Gb stick and one 8 Gb stick, the full 2 Gb in one stick and only a quarter of the 8 Gb in the other will interleave, totaling only 4 Gb in dual channel and the remaining 6 Gb in lower performing single channel. Having only 4 Gb in dual channel is better than nothing. Having 10 Gb is therefore better than having 8 Gb, even if the 2 Gb were slower than the 8 Gb stick, but of course you should aim higher and get an equally faster and hopefully larger stick to go with the other one.

Should I get a single 16GB RAM or 2 8GB RAM? Which is better?

Though it’s theoretically possible to get faster performance from 2 chips than one, the likelihood is rather slim that you’d notice this difference. Especially these days. Also, this is only possible if both chips are clocked similarly. By preference they should actually be made in the same batch by the same manufacturer - i.e. a paired set. If you’re buying two individual chips separately (or worse two different models / manufacturers) I would definitely suggest you rather go with one only.I’d say that for future proofing it’s probably better to go with one chip (if the motherboard only has 2 slots). Though even that should be a rather minor consideration. At what time are you going to think about upgrading 16GB of RAM? if at all? It may be that in that future date you’d be hard pressed to find matching RAM, it may even be a situation of needing to find old second-hand stuff. So such future proofing may actually be a red herring.So if you’ve got no special reason between choosing such double or single chip arrangement … there’s really nothing in the choice. Other than a possible slight (like in a handful of % points faster) performance, there’s no real benefit either way.However, there may be other considerations which could sway the choice one way or the other. E.g. buying the RAM in one arrangement may be cheaper. You may get better rated RAM one way or the other (e.g. higher clock speeds, lower latency, better track record of manufacturer, etc.). Even such things as physical space in the computer may matter - e.g. 2 chips may be less easy to keep cool than 1, the 2nd may get in the way of things like drive cables. But all that is conjecture - you’ve not stated any details, so all I can do is imagine different scenarios.

Can I add an 8GB RAM to a DDR3 laptop that already has a 4GB one, without removing the 4GB?

I find dual channel is overrated for normal people use.TL;DR version - Size of memory Is king as long as you use “nearly all of it” There is no reason for you to have 64 gigs of memory in your computer if you are using only 6. If you can cover your usage of memory then dual channel and speed is more important.In my extreme budget era I used whatever Memory module I could get my hands on for free, not looking on any aspect of it. I even remember running 64MB + 128MB+ 512MB modules at the same time and each time i added some I saw performance increaseFor normal use there will be noticeable difference between 4 and 8 gigs ( If you decide to go 4+4 dual channel. I was using single 8 gig module for quite a long time myself and was doing OK.However I found out that often times 8 gigs were not enough for me (I ran zilions open tabs in Chrome had a movie running and two games i was switching between) I then installed a second 8gig modue and everything got running a bit finer.So in your case installing 4+8gig module would definitely work, but unless you plan on running very memory consuming programs or run lots of programs simultaneously installing another 4gig module should be better.In case you decide to install another 4 gig try to get one with same frequency and clock as well. (I.E. 1600MHz, CL9-9-9-24) You can find out what frequency and memory you have now by using diagnostic tools available for free online.To further explain the worst thing that can happen to your memory is that you need to use more of it than there is available. At that point system will start swapping - saving parts of memory that it expects not to be used in near future to your hard drive, which takes AGES.I read nice illustration recently on Quora - Imagine you have a truck capable of going 60kph that can take 4 Tons of material and one that can do only 50kph, but can take 8 Tons of material. Which is better to transport a) 3 Tons of material b) 6 Tons of material? Memory is quite the same.