#vintagecomputers

🎄💾🗓️ Day 4: Retrocomputing Advent Calendar - The DEC PDP-11! 🎄💾🗓️

Released by Digital Equipment Corporation in 1970, the PDP-11 was a 16-bit minicomputer known for its orthogonal instruction set, allowing flexible and efficient programming. It introduced a Unibus architecture, which streamlined data communication and helped revolutionize computer design, making hardware design more modular and scalable. The PDP-11 was important in developing operating systems, including the early versions of UNIX. The PDP-11 was the hardware foundation for developing the C programming language and early UNIX systems. It supported multiple operating systems like RT-11, RSX-11, and UNIX, which directly shaped modern OS design principles. With over 600,000 units sold, the PDP-11 is celebrated as one of its era's most versatile and influential "minicomputers".

Check out the wikipedia page for some great history, photos (pictured here), and more -

And here's a story from Adafruit team member, Bill!

The DEC PDP-11 was the one of the first computers I ever programmed. That program was 'written' with a soldering iron.

I was an art student at the time, but spending most of my time in the engineering labs. There was a PDP-11-34 in the automation lab connected to an X-ray spectroscopy machine. Starting up the machine required toggling in a bootstrap loader via the front panel. This was a tedious process. So we ordered a diode-array boot ROM which had enough space to program 32 sixteen bit instructions.

Each instruction in the boot sequence needed to be broken down into binary (very straightforward with the PDP-11 instruction set). For each binary '1', a diode needed to be soldered into the array. The space was left empty for each '0'. 32 sixteen bit instructions was more than sufficient to load a secondary bootstrap from the floppy disk to launch the RT-11 operating system. So now it was possible to boot the system with just the push of a button.

I worked with a number DEC PDP-11/LSI-11 systems over the years. I still keep an LSI-11-23 system around for sentimental reasons.

Sinclair ZX Spectrum 128K

In 1985, Sinclair Research unveiled what would become the last and most powerful member of the legendary Spectrum family — the ZX Spectrum 128K.

After the enormous success of the ZX Spectrum 48K, which had defined home computing in the UK and Europe, Sinclair aimed to take the next step: to make the Spectrum not just a gaming machine, but a truly capable home computer for both entertainment and productivity.

Codenamed “Derby”, the 128K was originally developed for the Spanish market (through Sinclair’s local partner Investrónica), before launching in the UK in early 1986.

A leap in capability

At its heart was the same Zilog Z80A processor running at 3.5 MHz, but now backed by 128 kilobytes of RAM — a massive jump that allowed for larger, more ambitious software.

The machine introduced:

The AY-3-8912 sound chip, delivering rich 3-channel music.

Two memory banks, switchable between 48K and 128K modes, for full compatibility with older games.

A redesigned 128 BASIC interpreter with a built-in menu system and on-screen editor.

RS-232, allowing advanced users to connect printers.

Legacy

Although the 128K arrived just as the 8-bit era was beginning to fade, it marked the end of an era with style. It was the last Spectrum designed by Sir Clive Sinclair’s original team, before Amstrad acquired the brand and released the +2 and +3 models (with built-in cassette and floppy drives).

Even today, nearly 40 years later, the Spectrum 128K remains a symbol of British ingenuity: affordable, creative, and full of charm. For millions of Europeans, it wasn’t just a computer — it was their first window into programming, gaming, and digital imagination.

🎄💾🗓️ Day 8: Retrocomputing Advent Calendar - Commodore PET 🎄💾🗓️

The Commodore PET (Personal Electronic Transactor) came out in 1977 and was among the earliest personal computers - featuring an all-in-one design with a keyboard, monochrome monitor, and cassette deck - all within a single chassis. Powered by an MOS Technology 6502 microprocessor running at 1 MHz, it had 4 KB of RAM and was expandable up to 96 KB in later models. The PET had Commodore BASIC stored in ROM, allowing users to write and execute programs directly. Its display supported text resolutions of 40×25 or 80×25 characters, using the PETSCII character set for semigraphic capabilities. While early models did not have sound, later versions included a basic beeper. PET's all-in-one design and user-friendly interface contributed to its popularity in education and business, and it sold approximately 219,000 units before its discontinuation in 1982.

Check out the wikipedia page for some extended history and great photos -