I read the review of another customer who was frustrated about the fact that the book is only good for KEIL C51 which costs around 2000$. To my fate, when I started learning about Microcontroller, I started with this book and so, I believed that Keil C51 is THE language for microcontroller :) anyway, I spent days and months on internet, searching on reviews and found that, Keil C51 is the BEST for serious Engineers who cares about efficiency in real time. But I learned Microcontroller when I was in the University as a student and I could never afford to buy Keil uVision. But hey, Keil provides a Trial version which can compile code which cannot be more than 2KB in Size and the target device cannot be less than 2KB. So, if you want to learn C51 without purchasing, you still have the option. Later, I found many other alternatives to microcontroller programming like Small C and others, but, none is closed to Keil C51. So, if you are serious about learning Microcontroller programming, why wont you start learning the best compiler from the beginning!! This book was SOOOOOO Interesting and Exciting for me as a beginner that, I was feeling like a hero when I followed this book's simple instructions to setup my 8051 circuit, wrote simple C program and made my LED flashing, oweeeee :)) It was a great pleasure indeed.