MODEL 3040 DISK CONTROLLER SYSTEM REFERENCE MANUAL FOR THE PDP-8

This reference manual describes the System Industries Model 4400/4500 Disk Systems, specifically focusing on the integration of the Model 3040 Disk Controller with PDP-8 Series Computers. The system offers versatile bulk storage solutions by combining the Model 3040 Controller with either Diablo moving-head disk drives (for large capacity and removable media) or Applied Magnetics Corporation (AMC) fixed-head disk drives (for fast access), or a combination of both. The 3040 Controller supports up to four independent disk drives, and its programming is designed to be independent of the specific disk configuration.

Key aspects covered include:

• System Configuration and Capabilities: Details how Model 4400 (fixed-head) and 4500 (moving-head) systems can be configured, emphasizing the Model 3040 Controller's ability to interface with various drive types (Diablo Model 43/44, AMC Model 200-D) via its four parallel ports.
• Data Transfer Operations: Explains disk addressing, where data is organized into sectors (256 12-bit words, 16 sectors per track for PDP-8 systems). Commands and status information are handled via Program I/O, while high-speed data transfers utilize the Direct Memory Access (DMA) facility. The controller automatically manages block transfers across sector, track, and cylinder boundaries.
• Functional Features: Describes core functionalities such as combined seek-read/write operations (simplifying programming), automatic address verification for moving-head drives, a double buffering scheme to optimize data transfer timing, and robust error checking (identifying nine types of errors related to both disk drives and the controller).
• Advanced Capabilities: Highlights additional features like bad sector indication, write protection (through a bit in the Track Address Word for moving-head drives or physical switches for fixed-head drives, with a format switch override), and overlap seeking. Overlap seeking allows head positioning on one drive to occur concurrently with data transfers on another, significantly improving system response times. The system also supports interrupt generation and skip-on-condition instructions for efficient transfer monitoring.
• Controller Architecture and Instructions: Provides a detailed breakdown of the controller's programmable registers (Control, Status, Seek Status, Seek Address, Track Address, Sector Address) and internal, non-programmer-accessible registers (Word Count, Current Address, Data Shift, Buffer Interface, Arithmetic Check). It outlines the disk sector formats for both fixed-head and moving-head drives, including preambles, track address words, data, and Cyclic Redundancy Check (CRC) words for data integrity. A comprehensive list of PDP-8 I/O instructions (e.g., DSDD, DLCR, DRSR, DLSS, DLTR, DLTW, DWCA) is provided, along with explanations of controller operations such as master clear, read/write sequences, and disk formatting procedures.

The manual aims to provide users with a complete understanding of the system's functional descriptions, operational procedures, checkout, and diagnostic information, including necessary diagrams and schematics for installation.