first memory is a type of random access memory or ram for short; the memory used by a computer to hold data while it is being processed by the cpu and the programs running on the computer to perform a task at the request of the user program being executed.. a cache is a special form of first memory and is much faster because it is built right into the cpu of a modern computer system rather than relying on main memory which may be in a different location on the motherboard of the computer or located on another separate circuit board attached to the system bus to send requests back and forth to the actual main memory of the computer this speed increase in performance usually comes from putting instructions such as instructions for loading a program into the instruction caches so that those instructions are immediately available and can be executed by the processor without having to wait for the slower external memories of the main board to draw the instructions out of the high speed main memory of the computer as these tasks have to be performed in order to run any computer program which may not be quick because it may have to access one of more actual memories attached to either part of the central processing unit or if the operating system or the gui is running which is normally referred to as multi-tasking the operating system may be drawing data from the hard disk but to do this it has to read the content of the disk from head to tail thus making the activity of reading from the disks extremely slow resulting in a slowdown in the overall performance of the pc due to the processor having to spend a lot of time waiting for the contents of particular files to be pulled from the hard disk drives.