The New Testament in the King James was translated from the Textus Receptus. Here are a few of the highlights from the article:
Erasmus also lacked a complete copy of the book of Revelation and was forced to translate the last six verses back into Greek from the Latin in order to finish his edition.
It is now widely accepted by textual scholars that the selection of manuscripts available to Erasmus was quite limited — due partly to his time constraints, partly to geographic isolation before high-speed transit, and partly to the fact that many important texts were as yet undiscovered — being confined to a few late medieval texts that most modern scholars consider to be of dubious quality.
The majority of textual critical scholars have adopted an eclectic approach to the Greek New Testament, with the most weight given to the earliest extant manuscripts, which are mainly Alexandrian in character, thus breaking with the Textus Receptus in numerous places.
In summary, Erasmus, the compiler of the Textus Receptus, didn't have access to many of the earlier manuscripts that we now have access to. The current thought of biblical scholars, which I agree with, is that a manuscript is more accurate the closer it is to the date the of the original authorship. Consequently, this means that the accuracy of the translation of the New Testament in the King James Version isn't as accurate as some of the more recent translations.
The Old Testament of the King James Version is taken from the Masoretic Text. This text is pretty much accepted as the authority on the Old Testament and is used in most English translations.
watch out for the potholes.