A Restored PDP-11/83: Hosting via 2.11BSD Unix

Current Status: LIVE | OS: 2.11BSD | Activity: TMOG-11 Monitoring

Connecting to the PDP-11... Awaiting system snapshot (cached 5s).

🧬 Digital DNA: 1980s Engineering, Modern Refinement

This project showcases the raw power of the PDP-11, polished with contemporary restoration techniques. The system is a PDP-11/83 featuring a Mentec M11 processor, spanning two chassis and utilizing a hybrid of original DEC and Emulex controllers.

By combining classic magnetic tape, legacy disks, and serial terminals with the 2.11BSD operating system, this setup maintains a living link to computing's heritage.

🏗️ System Architecture & Hardware

The CPU Complex

The heart of the machine is the Mentec M11, a single-board PDP-11 compatible CPU. This modern replacement has superseded the ~~M8190~~ and two separate memory boards by integrating both the processor and RAM onto one piece of silicon.

Memory: Integrated onboard RAM.
Monitoring: Physical RAM usage and swap space are tracked via TMOG-11.
Addressing: The system utilizes a 22-bit memory management scheme, meaning the addressable space is: $\text{Total Addressable Memory} = 2^{22} \text{ bytes} = 4 \text{ MiB}$

Bus & Timing

The system is built around the Q-bus architecture, utilizing two chassis linked by an M9404 (source) and M9405 (target) pair. This allows for expanded connectivity for serial I/O, Ethernet, and storage.

🛠️ The Controller & Storage Stack

The system employs a sophisticated array of controllers to bridge legacy media to the Q-bus:

Controller Specifications:

M7555 $\rightarrow$ RQDX3: Handles MFM disks.
Emulex UC07 $\rightarrow$ SCSI Bridge: Connects both disks and tape.
M8061 $\rightarrow$ RLV12: Manages dual RL02 drives.
M7504 $\rightarrow$ DEQNA: Provides Ethernet connectivity.
M7165/M7164 $\rightarrow$ KDA50 Pair: Interfaces with RA8x/RA9x MSCP drives.
M3104 $\rightarrow$ Serial Multiplexer: Manages multiple terminal lines.

Storage Media:

MSCP Storage: RA82 and dual RA92 drives (via KDA50).
Bootstrap/Swap: MFM hard disk (via RQDX3).
Field Media: Dual RX50 floppies.
Legacy Images: RL02 pair (via RLV12).
Archival: TKZ50 tape storage (via UC07).

🌐 Networking & Software Services

The machine runs 2.11BSD, a PDP-11 version of UNIX that includes a native C compiler and full networking capabilities.

Connectivity: Ethernet is handled by the DEQNA controller using the if_qe driver.
Web Presence: A lightweight HTTP server delivers this page.
Optimization:
- A front-end cache prevents the homepage from being overwhelmed by requests.
- TMOG-11 snapshots are cached every 5 seconds.
- Note: Browser updates pause automatically when the tab is hidden.

📋 System Inventory

Component	Primary Role
Mentec M11	CPU & Integrated Memory
M3104	Serial Multiplexer
M7555	RQDX3 Disc Controller
Emulex UC07 (x2)	Disc & Tape Controllers
M7504	Ethernet Controller
M7165 / M7164	KDA50 Controllers
M8061	RLV12 Disk Controller
M9404 / M9405	Bus Source & Target
RA82 / RA92	Hard Disk Drives
RX50	Floppy Drive
TKZ50	Tape Drive

⚙️ Maintenance & Reliability

The system is managed through a combination of hardware console access and modern version control.

Boot & Backup Workflow:

Primary boot via MSCP disk.
Secondary boot path via RL02.
Periodic imaging of RL02 drives.
Regular backup rotations to TKZ50 tape.
Source code and assets archived in Git.

Diagnostics: The console uses ODT (Octal Debugging Technique) for low-level memory and register inspection.

Example diagnostic logic:

; Check device register for KDA50
.C1200 
; Reset controller
.W1200 000100

The system maintains grant continuity across both chassis, ensuring the controllers operate as a unified whole.