Hi Maria,
One of the most cost effective ways to increase computer speed is by adding additional RAM. The cost of RAM is so low at the current time that other than changing the CPU, and that can be cost prohibitive, it is the most effective way to increase the performance of a PC.
When your system loads it looks at the available RAM and makes a determination as to how much RAM can be dedicated to store the the software being loaded. This includes parts of the OS and the actual applications that are being loaded as well. The more software, or portions thereof, that are loaded into RAM, the quicker the PC will respond to commands. The actual formula used to make this calculation can get complex because it is based on a variety of things. CPU clocking speed, number of available threads, available RAM, whether it is a 32 or 64 bit bus, shadow RAM, etc. But rest assured that the amount of physical RAM available is a key component in that determination.
With the current processors and the types of software being developed in the 64 bit bus line, 4GB of RAM is a an absolute minimum amount to run many applications, and at that configuration, your systems will run slow. With that configuration the applications are constantly swapping out what is stored in RAM with what is needed in RAM to access the software. This is swap files come into play in the execution of software. You may have read or heard about swap files as you were learning about PC's this is the type of information they are talking about.
I have to disagree with Muzzamil on one point he made. If you are working with video and making your own videos, 4GB of RAM would make that process extremely slow, in fact the software that I use to produce the training videos will not even run with less than 16GB of RAM. When you are compressing video into an MP4 format, and that is the recommended format for all web video, it is very process intensive and requires a tremendous amount of CPU speed and RAM.
On the disk speed that was mentioned. Most mechanical drives now are 7200 RPM drives, that is pretty much the standard. I have done a bunch of studies with my college classes and believe it or not, there is negligible difference in the read / write access between 5400 and 7200 speed drives. The drives reads and writes are more synchronized to the BUS speeds then the physical drive speeds.
If you really want a speed boost, go with an increase in RAM, as much as you can afford, and swap the physical hard drive with an SSD drive. That will show a very noticeable increase in performance. SSD's are becoming very affordable now and extremely fast.
Now on the hardware. Depending upon the MAC you have upgrading the MAC itself can be a challenge. Apple has never made it easy to upgrade their iMacs. I own two, a 27" iMac Retina 5K, and a 21.5 and have upgraded both but they take some special tools and you really need to be careful when you remove the front class.
I hope this helps.
If you have any questions let me know. There are some really good tools out there to clone the drives if you decide to upgrade to an SSD and if you go with upgrading the Windows system, adding RAM and a replacement drive is rather simple.
