A repository of bug-fixed and patched software projects for DEC PDP-11 systems, targeting real hardware, SimH, and PiDP-11 emulators running RT-11 and RSX-11M-PLUS. The two main projects are FIG-FORTH v1.4, which corrects garbled terminal output and a corrupted screen file, and FOCAL-11 V11-01C, which fixes an infinite recursion crash in the FEXP function.
- FIG-FORTH originally marked dictionary names with a high bit that modern terminals rendered as a literal "?" character; the patch strips it before display without affecting the dictionary
- The FORTH.DAT file was distributed with a VARIABLE RMS record format, embedding 2-byte length headers every 512 bytes that appeared as stray characters in screens
- FOCAL-11's XFEXP computed e^x by recursively halving the exponent until it fell below -8, but zero's exponent never decreases, so the recursion ran the stack into memory; all other math functions already had a depth guard
- FOCAL is a BASIC-like language from the late 1960s; Lunar Lander was originally written in it
- FIG-FORTH originally marked dictionary names with a high bit that modern terminals rendered as a literal "?" character; the patch strips it before display without affecting the dictionary
- The FORTH.DAT file was distributed with a VARIABLE RMS record format, embedding 2-byte length headers every 512 bytes that appeared as stray characters in screens
- FOCAL-11's XFEXP computed e^x by recursively halving the exponent until it fell below -8, but zero's exponent never decreases, so the recursion ran the stack into memory; all other math functions already had a depth guard
- FOCAL is a BASIC-like language from the late 1960s; Lunar Lander was originally written in it
The article argues that the perception of C as a “low‑level” language has become outdated.
- **Historical context** – In the early 1970s, C on the PDP‑11 was literally close to the metal: each statement mapped to one or two machine instructions, memory was flat, and the execution model was straightforward.
- **Modern hardware** – Today’s CPUs are far more complex (multi‑core, deep pipelines, out‑of‑order execution, vector units, large caches, speculative execution). They are designed to run legacy C code efficiently, but the underlying reality is far removed from the simple model that early C programmers relied on.
- **The illusion** – Modern processors adapt to preserve the old C abstract machine, giving developers the impression that C is still “low‑level.” This illusion hides a mismatch between what C promises (predictable, simple mapping to hardware) and what the hardware actually does.
- **Historical context** – In the early 1970s, C on the PDP‑11 was literally close to the metal: each statement mapped to one or two machine instructions, memory was flat, and the execution model was straightforward.
- **Modern hardware** – Today’s CPUs are far more complex (multi‑core, deep pipelines, out‑of‑order execution, vector units, large caches, speculative execution). They are designed to run legacy C code efficiently, but the underlying reality is far removed from the simple model that early C programmers relied on.
- **The illusion** – Modern processors adapt to preserve the old C abstract machine, giving developers the impression that C is still “low‑level.” This illusion hides a mismatch between what C promises (predictable, simple mapping to hardware) and what the hardware actually does.
* **Enigma Touch:** Jürgen Müller’s Enigma replica is now available for order, featuring a unique all-electronic design and a focus on replicating the original user experience. A Google Group has been created for discussion and related activities.
* **PiDP-1:** The PiDP-1 kit is nearing completion and expected to ship at the end of July, with both console and rack-mounted versions available. A Google Group has been launched for the PiDP-1 community.
* **ARPANET Reconstruction:** Lars Brinkhoff has made significant progress in reconstructing the ARPANET, allowing for connections between emulated PDP-10s and modern Linux machines. The project seeks volunteers to expand the network.
* **LGP-30:** Work is underway on a replica of the LGP-30, with a focus on creating an authentic 1950s metal case.
* **PiDP-10 & Software:** Updates on software for the PiDP-8/11, and a note about running the original Micro-Soft BASIC on a PiDP-10.
* **Whirlwind:** Initial planning for a Whirlwind replica is underway.
* **PiDP-1:** The PiDP-1 kit is nearing completion and expected to ship at the end of July, with both console and rack-mounted versions available. A Google Group has been launched for the PiDP-1 community.
* **ARPANET Reconstruction:** Lars Brinkhoff has made significant progress in reconstructing the ARPANET, allowing for connections between emulated PDP-10s and modern Linux machines. The project seeks volunteers to expand the network.
* **LGP-30:** Work is underway on a replica of the LGP-30, with a focus on creating an authentic 1950s metal case.
* **PiDP-10 & Software:** Updates on software for the PiDP-8/11, and a note about running the original Micro-Soft BASIC on a PiDP-10.
* **Whirlwind:** Initial planning for a Whirlwind replica is underway.
The December 2024 newsletter from Obsolescence Guaranteed covers updates on new projects such as PiDP-10 and PiDP-1, news about existing projects like PiDP-8 and PiDP-11, and upcoming plans for 2025 including a PiDP-1 replica and an annual programming competition.
CEDS is a retrocomputing micro-factory, producing and shipping PiDP-10 replica kits. They also offer assembled PiDP-11 units, with the option of selecting assembled or unassembled kits in the order form. For placing an order, fill in the required information and submit the order form.
