Fastest means of memory access for CPU is Registers.

Registers:

- Registers are small, high-speed storage locations within the CPU.
- They are used to hold data that is currently being processed by the CPU.
- Registers are the fastest means of memory access for the CPU because they are located directly on the CPU chip, and can be accessed very quickly.
- Registers are used to hold instructions, data, and memory addresses.
- Registers can be used to store data that is needed frequently, such as loop counters, index variables, and other frequently used variables.
- Registers are also used for temporary storage of data between CPU operations.

Cache:

- Cache is a type of high-speed memory that is located between the CPU and main memory.
- Cache is used to store frequently accessed data and instructions.
- Cache is faster than main memory, but slower than registers.
- Cache is used to reduce the amount of time that the CPU spends waiting for data to be retrieved from main memory.

Main Memory:

- Main memory is the primary storage area for the computer.
- Main memory is slower than registers and cache, but larger in size.
- Main memory is used to store programs, data, and other information that is not currently being processed by the CPU.
- Main memory is accessed via the memory bus, which connects the CPU to main memory.

Virtual Memory:

- Virtual memory is a technique used by operating systems to expand the amount of available memory.
- Virtual memory allows the computer to use hard disk space as if it were main memory.
- Virtual memory is slower than main memory, and is only used when the computer runs out of available physical memory.
- Virtual memory is accessed via the paging system, which allows the computer to move data between main memory and the hard disk.

Registers are the fastest means of access for CPU. Registers are the small memory locations which are present closest to the CPU.