The designation RAM is critical - as well as the question where they are located.

Thanks Aparna - your link is great!

In the AVR architecture all registers are 'memory-mapped' - meaning they can be addressed like any other RAM location. 'Register' only indicates, that these memory locations have 'some special functions' associated with.

Thus I'd expect the 'registers' to be located in a special 'register RAM block', as the additional functions (as compared to a 'normal' RAM cell) require additional connections in the physical layout.

But 'in the CPU'? What exactly is 'the CPU'? The arithmetic unit? The address unit? The control unit? ...

These slides by Prof. Stephen J. Kuyath explain the internal architecture of the AVR: http://webpages.uncc.edu/~sjkuyath/ELET3232/Topics/Topic%203-AVRarch.pdf

Note that the CPU is only one element of the MCU (microcontroller unit) and that there exist many variants of AVR-based MCUs. Some examples are included in the above slides. Another example is shown here (notice the CPU in the middle): http://jcole.us/blog/files/avr-block-diagram-large.png

The registers are addressable both as general purpose registers in register-mode instructions and as RAM addresses 0 - 1F

 Aparna Murthy  actually i was confused when i see memory map in which RAm is divided into three sections named as GPRS SFRS and SRAM but thanks for your help.

Yannick Le Moullec U Thank for the lecture link its very helpful for me.  Dreher   Andrew Wolfe   thanks for your answer sir .

The registers are present in the specific area of RAM(Data memory), that is present inside the CPU. All these registers are addressable. PC and status register address will be available in the data sheet.

E.g: 

8051's status register address: D0H

http://www.circuitstoday.com/8051-special-function-registers-and-ports

Thank you Saranya B