It would be good to say which book and edition you are referring to as the book as it comes in 3 languages and has been revised over time. In general, the radix is the base numbering of the system. For a decimal base numbering system the radix is 10 and for (111…11)2 the radix is 2. The LSD, least significant digit is on the right and the MSD, most significant digit is on the left. So in your example, 1 x 2 to the 0 is the LSD, the digit to the left of that is 1 x 2 to the 1, followed by 1 x 2 to the 2, etc. ((111…11)2 = 1 x 2^0 + 1 x 2^1 + 1 x 2^3…). The number 800 in the decimal base numbering system in radix notation would be (800)10 = 0 x 10^0 + 0 x 10^1 + 8 x 10^2 = 800.