Data visualization in IoT is essential for monitoring and understanding data. It allows stakeholders to interpret complex data easily, identify trends, and make informed decisions. Effective data visualization is crucial for deriving actionable insights from IoT data.

The main difference is that a general-purpose OS is not optimized for resource-constrained IoT devices. IoT OS is designed to run efficiently on devices with limited processing power and memory.

Early IoT was primarily focused on industrial automation and monitoring. It was used to improve processes, gather data from sensors in manufacturing and logistics, and increase efficiency in various industries. IoT's roots can be traced back to applications like remote monitoring and control of industrial equipment.

Blockchain technology offers a decentralized ledger for secure and transparent transactions, making it a potential solution for enhancing IoT security. It provides immutable and auditable records of transactions, improving trust and security.

The integration of IoT with cloud services is often facilitated by AWS IoT Core, which is a managed service for IoT that provides secure and scalable connectivity to the cloud. MQTT, Docker, and Apache Kafka are relevant technologies but do not provide the same level of cloud integration as AWS IoT Core.

The combination of IoT and Big Data has given rise to streaming analytics, which processes and analyzes data in real-time. This enables immediate decision-making based on the data generated by IoT devices.

Blockchain integration in IoT is especially beneficial for maintaining data integrity. Blockchain's tamper-proof nature ensures that data remains unaltered, enhancing the trustworthiness of information in IoT applications. Device Availability, Real-time Data Processing, and Energy Efficiency are important but not the primary focus of blockchain integration in IoT.

Machine Learning in IoT is primarily used for predictive analytics. It involves using historical data to make predictions and decisions, a key aspect of IoT applications.

For a medical wearable device requiring immediate response times, an RTOS is the best choice. RTOS is designed to handle real-time applications, making it ideal for critical functions. General-purpose, mobile, and network operating systems may not meet the stringent timing requirements of medical wearables.

Zero-Day attacks target vulnerabilities in IoT devices that are not yet known to the manufacturer or the public. Exploiting these undisclosed weaknesses can lead to unauthorized access or compromise of the device, making it a significant security concern.