The above explains that a computer speed is dependent not only on the CPU processor speed, but also memory size and disk speed.
Processors are usually stated in the number of cores and the speed (labeled in GHz or Gigahertz) of the processor. The speed of the chip will tell you how much data it can process. 1 GHz implies the clock frequency of the CPU is 1 billion, and higher this number is the faster it can process instructions! Therefore, the bigger the number, the faster it can execute the instructions and make your computer run faster. The number of cores implies how many processors are there within one physical processor. For example, older processors were single cores, so if the speed was listed as 2 GHz, that how fast it was able to execute instructions. Then came two core processors. A 2 GHz processor having two cores is similar to a 4 GHz processor. The reason industry chose to use multiple cores in a processor versus a faster single core as it was becoming extremely expensive and challenging to build faster processors beyond 4 GHz. Now the standard for processors for laptops and desktops is 2 cores to 4 cores. Therefore, the greater number of cores, the better. For powerful servers, the number of cores can be 12-14 cores!
If the memory is too small, which in todays world, 4 GB is small, then whenever the CPU is unable to find the required information in its memory, it will have to offload some information from its memory and load the required information from the hard drive therefore slowing your computer down. 8GB would be minimal in today’s world for reasonably fast processing if you are using your computer for web surfing and handling small to medium documents in Word and small to medium spreadsheets in Excel. This user class is defined as a light user. If you are wanting to handle larger documents, spreadsheets and graphics, i.e., medium user, 12 GB would be better. If you are a heavy user dealing with very large graphics, videos, 3D, Engineering drawings, then 16 GB and upwards would be better.
Hard drives speed is also very important as it affects how fast the files are loaded from hard disk to the memory and also when you save files to hard drive and copy and move files. Most laptops now come with 5400 revolutions per minute (RPM) hard drives that are faster than the older laptops that had 4500 RPM drives. But they are not as fast as desktop computers which usually come with 7200 RPM drives. Therefore, you may see that the desktop machine seems more powerful even if the CPU and Memory may be similar. Powerful servers may have 10,000 RPM and 15,000 RPM drives in them! As the laptops have slowest hard drives that can affect performance, a better option is buy laptops with Solid State Drives (SSD) drives. SSD drives can be 10 to 50 times faster than hard drives. However, they are more expensive and come is smaller sizes. 256 GB SSD is fine if you are light user. If you are a medium user, 500 GB SSD or larger would be much better. Apple Macintosh laptops always seem to start and operate much faster as they mostly have SSD drives. In powerful servers, multiple SSD drives are combined together to give larger capacity and improve speed.
In summary here is a table that explains what you may want to consider: