TU58 Engineering Specification Jun78

This document is an Engineering Specification for the Digital Equipment Corporation (DEC) TU58, a low-cost mass memory device, dated June 27, 1978.

Here's a summary of its key aspects:

1. Product Overview: The TU58 is a mass memory device that uses 3M DC-100A tape cartridges. It is designed to provide random access to data records and can support one or two drives. Each cartridge has a capacity of 262,144 bytes, organized as 2048 records, each 128 bytes in size.

2. Configuration & Physical Characteristics:

   • It consists of one or two cartridge drives and a control module containing read/write circuits and firmware.
   • The unit can be integrated into a host system (terminal or processor), or mounted as a stand-alone or rack-mount unit.
   • Various component and subsystem designations are defined (e.g., TU58-XA for drive/cable, TU58-CA for a rackmount subsystem).
   • Detailed dimensions are provided for the controller board, drive module, cage, and rackmount unit.

3. Interfaces:

   • Supports both parallel (TTL) and asynchronous serial interfaces.
   • The serial interface is compatible with RX-232, RS-422, and RS-423 standards, operating in full duplex with selectable baud rates ranging from 150 to 38.4K baud.
   • Power requirements are specified for both module/drive and rackmount configurations.

4. Data Format & Recording Scheme:

   • Data is recorded using ratio encoding at a density of 800 bits per inch (BPI) / 2400 flux reversals per inch (FRPI).
   • Special marks (Beginning of Tape - BOT, End of Tape - EOT, and Inter Record Marks - IRM) are used for tape formatting and record demarcation.
   • Data is organized into records with headers that include sync, record numbers, and checksums. A 16-bit checksum is used for error detection.

5. Performance & Reliability:

   • Average access time to any record is 9.3 seconds, with a maximum of 28 seconds.
   • Read/write tape speed is 30 inches per second (IPS), and search speed is 60 IPS.
   • Data transfer rates are specified for both parallel and serial interfaces.
   • Reliability metrics include low error rates for searches, soft data (recoverable), and hard data. Mean Time Between Failures (MTBF) is 1000 hours at 100% duty cycle, and Mean Time To Repair (MTTR) is less than 0.5 hours.
   • The TU58 is designed to meet DEC STD 102 for Class A environmental devices.

6. Software Interface (Radial Serial Protocol - RSP):

   • The TU58 is controlled by a high-level command set, which offloads tape-related operations (like positioning and retries) from the host.
   • Communication between the TU58 and the host occurs via message packets, each starting with a flag byte (defining the message type, e.g., DATA, COMMAND, INIT, CONTINUE, XOFF) and ending with a 16-bit checksum.
   • Data transfers involve multiple packets (command, 128-byte data chunks, and an end packet).
   • The document details a command set that is a subset of a standard random access mass storage device command set, including commands for initialization, reading, writing, positioning, diagnostics, and status retrieval. Error reporting is detailed via success codes and summary status bits in end packets.