which is better 4gb or 8gb Mac book pro

What's better, 8gb is always better. But you also don't want to waste money on computing power you won't use.

What software are you going to be using?

With today's hardware, I'd really say 4gb is minimum and 8gb is more of a standard. If you were doing heavy graphic editing software, or other software that is ram heavy, 16gb or even 32gb would be even better.

The custom built PC I'm using now is 32GB, and the one my boss has is 64GB of ram. Overkill....sure, but it only was another $150 on a $3000 computer, so why not.

That's why it's important to know what software you expect to use.

Also, ram is cheap (relatively), and easy to upgrade/install yourself (relatively). Ram from Apple is unnecessary expensive. Shop it, but I don't think it's ever cheaper to buy Ram upgrades from Apple. You're better off buying the computer, and buying the ram separate, and than installing the extra ram into the computer. It's not hard, there are tutorials online, but even if you don't want to do it, I bet a local computer repair shop could get you the correct ram, and install it for you still for a fraction of what Apple is going to charge you.

This is one area I'm really dissapointed in how Apple deals/charges with/for.

oh ok , So, a 4g do have enough room to do a Android and IOS course

Kevin Korte , sorry i was asking a lot of question . I am totally new to Mac book pro because I always use PC for my projects

Yeah 4gb would be enough, but again, it's a bit old to stay at 4gb. 4gb was the standard back in 2011, now it's 8gb and soon enough will be 16gb.

Ram is ram, whether it's PC or Mac, it functions the same. It's Random Access Memory. It's where your computer stores bits of information to be quickly retrievable. Your ram memory is completely wiped every time you shut your computer off.

Think of it like this. You have a huge stack of papers to work with. The bigger your desk, the more you can spread all the papers out and quickly find what you need. The smaller the desk, the longer it'll take to find a particular paper because you don't have room to spread things out to see it. Ram is a workspace for bits of information your computer is working with in real time.

Throw me some links of particular computers you are looking at. Do you have 3-4 models you're considering from the refurbished list?

Everyone's value == performance guides are different.

Kevin Korte, http://www.amazon.com/Apple-MacBook-Pro-15-4-Laptop/dp/B000BNHM0C/ref=sr_1_5?ie=UTF8&qid=1443225578&sr=8-5&keywords=mac+book+pro and http://www.amazon.com/dp/B007471D2Q/ref=twister_B008AZGKQ0?_encoding=UTF8&psc=1 the link is from amazon.com

Depending on your budget and the price difference it looks completely up to you. The laptop you are looking at is actually quite a deal for a macbook. It comes with i7, upgradable ram to 8gb and quad core. Personally, if you can afford to both wait and even afford a brand new laptop, I would wait and get a Macbook with Skylake. Based on what you are you using the laptop for though, this looks like it would be sufficient.

8GB if you are just running OS X, 16GB if you are running virtualization software like Parallels. The first option is substandard. Even a Mac with a lot of memory needs to call purge a lot, just don't do it until you quit any heavy duty apps.