Final answer:
A TaskTracker is a component of Apache Hadoop that executes tasks on nodes in a Hadoop cluster. There is one instance of TaskTracker per node, each capable of running multiple tasks simultaneously. In the newer versions of Hadoop, TaskTracker has been replaced by YARN's Application Master and NodeManager.
Step-by-step explanation:
A TaskTracker is an essential component of Apache Hadoop, which is responsible for executing tasks in a Hadoop cluster. When a Hadoop job is executed, the JobTracker (another component of Hadoop) sends out the code to run on different nodes across the cluster, assigning these tasks to specific TaskTrackers.
Each node in a Hadoop cluster will run its instance of TaskTracker, and each TaskTracker has a set number of slots for running tasks. Essentially, the number of TaskTracker instances corresponds to the number of nodes in the cluster. However, with multiple slots in each TaskTracker, it can handle multiple tasks simultaneously.
It's important to know that Hadoop's architecture has evolved, and in its more recent versions (Hadoop 2.x onwards), TaskTracker has been replaced by Application Master and NodeManager components as part of the YARN (Yet Another Resource Negotiator) system.