Can I,install Win 7 or Win 8, beside the Mac OSX, without slowing down the system,or make it slow down?

Yes, you need to purchase a windows 7 or windows 8 install and then you can install it using Bootcamp which creates a second partition on the hard drive. Use the Bootcamp Utility application within your Utilities folder in the Applications folder.

Typically yes. But there is a scenario where installing Windows using Bootcamp Assistant will slow down your computer. For example, say you have a 500GB hard drive and you have used 240GB for OSx and your data. You then create a Bootcamp partition of 250GB for Windows. This leaves 250GB for OSx but you have already used 240GB leaving only 10GB free for OSx to use. This scenario will slow your OSx significantly since you no longer have enough free space for OSx.

You need at least 20% of your HDD free for your system to continue to run smooth. So, it depends on how big of a partition you create for Windows and how much hard drive you leave for OS X.

1234khashayar wrote:

Which means, if I Set More Space for The OS X, It will not Slow Down, Right?

What do you mean? You need at least 20% free space on your OSx partition. You need at least 100GB partition for Windows and your Windows data. So do the math. If you have a 300GB hard drive and you make a 100GB partition for Windows that leaves 200GB for OSx and your OSx data. So the most you can use on your OSx partition for OSx and data is 200 - 20% = 160GB. If you have more than 160GB of OSx and OSx data then your computer will slow down when running OSx.

It would be helpful if you provided your hard drive capacity and current free space to us so that we don't have to continue making up scenarios.