CPU

• CPUs carry out the instructions of a computer program. The clock speed of a CPU measures the speed, measured in megahertz (MHz) or gigahertz (GHz), at which it processes instructions. A CPU with a clock speed of 1.8 GHz will greatly outperform a CPU that runs at 900 MHz.
  
  

RAM

• RAM, commonly called "memory," serves as the PC's temporary storage memory. RAM allows a PC to retrieve temporary data, which proves useful when using software. Increasing a PC's RAM is a fast and cheap way to improve its speed.
  
  

Hard Disk Drives

• Hard disk drives determine the speed at which the PC boots up, programs load and digital media performs. The speed of a hard disk drive hinges on its capacity space, measured in gigabytes, and its rotations per minute (RPM). Though expensive, upgrading a hard disk drive offers numerous benefits to a PC's speed.