Disk I/O Processing

This document describes the disk I/O processing architecture in the TOPS10 operating system, covering several critical areas:

• I/O Flow: Detailed steps for calculating cylinders, handling seeks, managing queues, and processing interrupts.
• Dual Port Handling: Logic for managing disk access across multiple channels, including primary and alternate path selection.
• Error Handling: Comprehensive procedures for dealing with ECC correctable errors, non-data errors, and data errors, including various retry sequences and offset adjustments.
• Exception Conditions: Explanations of status changes such as medium-on-line states, drive power-up, seek failures, hung devices, and RAE (Register Access Errors).
• Maintenance and Integrity: Procedures for managing bad block records (BAT blocks) and using the DSKRAT program to verify file structure consistency and disk allocation.