Retrocomputing

1637 Articles

At Last! CP/M For Protected Mode

August 4, 2026 by 34 Comments

If you used a serious computer pre-IBM PC, there was a fair chance its operating system was CP/M. CP/M was a staple among 8080 and Z80 computers and while there were other versions, we’ll always associate CP/M with the Z-80. There was a CP/M made for the PC which used an 8088 (a hybrid 8-bit bus with a 16-bit 8086 core), but it was overwhelmed by MSDOS. However, there was another interesting version made for the 68000, and now [johnsonjh] has ported that over to create an early version of CP/M for 80386 protected mode.

The Z-80 only had a 16-bit address bus, so it could only handle 64K of memory. It was common to “bank switch” some memory, and CP/M Plus could be made to understand that (for example, you might have 32K of common memory and three banks of 32K memory; you could address one bank at a time). However, the 386 had a full-blown memory management unit that could remap physical 4K memory pages to anywhere in a program’s virtual address space.

Ordinary CP/M couldn’t handle that, but the Motorola 68000 had a similar page management model, so it makes sense it might be easier to port CP/M-68K to the 80386 than starting from the original, even though the instruction set for the Z-80 is conceptually more similar to the 80386.

What can you do with it? We don’t know. Presumably, it will allow you to use lots of memory. Historically, CP/M software from one variant would not run on another, so you’ll have to build anything you want to use. Of course, the real killer for lots of CP/M memory was multitasking, but that takes MP/M, and only about half of that is currently working. But we won’t be surprised to see it completed soon.

While CP/M skills won’t land you many jobs these days, it is a pretty good way to get mentioned on Hackaday.

Un Ordinateur Pour Le Minitel-1 (A Computer For The Minitel-1)

August 4, 2026 by 10 Comments

In the 1980s, France was the stage for one of the boldest public computing projects of the era. Minitel was the French take on viewdata, and instead of making it an expensive and unattainable luxury, they made the terminals universally available. Many Minitel services cost extra to use, but despite this it was a runaway success that lingered on into the 21st century.

The ubiquitous terminals are now surplus to requirements, but that’s not to say they are useless. [MemoireMorte] has proved this with the Memo-1, a 6502-based computer designed to plug into a Minitel-1 terminal. It’s just the accessory your Minitel needs!

Hardware wise it’s a relatively conventional device with the usual RAM, ROM, and BASIC. There’s an expansion port, and a 6522 to provide a couple of Atari joystick ports. The serial port uses a a 6551 ACIA rather than the more usual W65C51 because of an incompatibility between the latter chip and the Minitel-1.

We like this computer, not because of novelty, after all it’s hardly the first 6502 we’ve seen, but because of its use of the Minitel terminal. These devices are magnificent, and deserve more love. We subjected another terminal to a teardown a year or two ago.

A Versatile PDP-11/70 Emulator

August 3, 2026 by 8 Comments

The PDP-11 was a 16-bit minicomputer that was very influential in its time. That’s what inspired [vanheusden] to start working on an emulator for the machine in 2018, which has since been developed to run on a wide variety of platforms. 

The emulator, named “Kek,” is quite capable, able to run Unix 5 up to an d including Unix 7 in multi-user mode, along with BSD 2.11 Unix depending on what it’s running on. It also supports classic hardware like RK05, RL02, RP06, and RP07 disks, the KW11-L line time clock, and the DC-11 serial line interface. The emulator can also run on a wide variety of platforms. It’s possible to run it on a standard Linux machine if so desired, or you can run it on BSD, MacOS, or Windows if so desired. Beyond that, you can even get it going on a Teensy 4.1 or an ESP32 if that’s more your jam. Modern microcontrollers are just that powerful that emulating a PDP-11/70 just isn’t a challenge anymore.

We love seeing old machines emulated and brought back to life. It’s funny to see how often it’s done on microcontrollers instead of full-scale PCs these days, too. Video after the break.

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Energizing A Vacuum Tube Flip-Flop Module Of The IBM 604

August 3, 2026 by 10 Comments
Reverse-engineered schematic of the IBM 604's TR-3 module. (Credit: Ken Shirriff)
Reverse-engineered schematic of the IBM 604’s TR-3 module. (Credit: Ken Shirriff)

Taking a break from ogling microscopic features in Intel’s semiconductor processors, [Ken Shirriff] is back to instead poking at decidedly macroscopic pluggable modules from the 1948 IBM 604 Electronic Calculator. This time around it’s one of the so-called trigger modules in the form of the TR-3, which uses a flip-flop circuit to implement the timing signals and pulses that made the 604 work.

This differs from the thyratron module that we covered previously. A thyratron is a high current switch and rectifier, which is useful more for the periphery of the computer system. These TR-3s on the other hand were used to implement the basic logic circuits, even if a flip-flop by itself seems rather boring, being just a circuit that toggles between two states.

In this TR-3 module we find a 2033 dual triode design which thus increases density by having the two inverters of the flip-flop in the same tube. The rest of the module is taken up by the requisite capacitors and resistors that complete the circuit. After wiring up this original module, [Ken] was able to make it trigger somewhat reliably, requiring a stable input trigger.

Notable is that in the IBM 650 from 1954 this flip-flop circuit was abandoned in favor of one based on diode logic, presumably to use more reliable Boolean logic instead of the much fussier analog interactions. Naturally, in the first transistorized computers the use of diode-transistor logic (DTL) was exceedingly common, so this makes a lot of sense.

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New File Manager Is C64’s Answer To Norton Commander

August 3, 2026 by 17 Comments

Norton was always a PC company — Norton Commander, the file manager that launched a thousand clones, was only ever available for DOS, like the rest of the company’s offerings in those days. If they’d decided to port it to the C64, though, it would likely look a lot like [retro3872809] aka [Chicken 64]’s Multi Floppy Commander with Turbo, available on GitLab.

As you might be able to see on the screen shot above or in the demo video below, the application provides an 80-column interface with a split view to show a pair of floppies side-by-side. Not that you’re limited to two floppies, however. The software is happy to swap between all the drives on the bus, to the C64’s maximum of four. All four drives will be usable since the file manager lives on a cartridge.

All drive models are supported, though not all have turbo. As a file manager, it looks like it has the normal functionality you’d expect: renaming, copying, moving and deleting files and directories. You can also launch programs or print disk listings, assuming you have a printer attached to your Commodore.

Said Commodore perhaps needn’t be vintage, as they’re selling new ones again, but if you want a disk drive you may have to fix it yourself.

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Casual Repair And Maintenance On An Amiga 1000

July 31, 2026 by 16 Comments

Recently [Drygol] had an Amiga 1000 system over for some repairs as well as maintenance and general TLC. This is a Motorola 68000-based home computer from 1985 that also has the distinction of being the first Amiga system to be released by Commodore. At a time when the IBM PC was still strutting its monochrome and EGA graphics alongside PC speaker beeps, the Amiga 1000 featured relatively high-res graphics and advanced stereo audio courtesy of special accelerator chips.

Overall the system was in a pretty good condition, even coming with the very nifty modern Parceiro expansion that adds 8 MB of fast RAM, an SD card slot and RTC. This thus meant that they mostly just had to perform the typical maintenance task, such as recapping the PSU and mainboard, as well as recapping and lubing up the floppy drive. The original 230 VAC fan in the PSU also got swapped with a 12V unit that was much quieter.

After disassembling the keyboard for some deep cleaning and retr0brighting, a little glitch in the form of the use of a too long screw by a previous owner was addressed, as well as a broken plastic clip. With how little attention the Amiga 1000 received after its release it’s good to see some of these units still kicking.

A Labour Of Love Brings A Kids Book To The Spectrum

July 27, 2026 by 37 Comments

Back in the early 1980s when 8-bit home computers became affordable educational toys for children, the traditional paper publishing industry did its best to keep up. For a few brief years, there were children’s books dedicated to the innards of a computer in meticulous detail, and courtesy of [Jason Jacques] we have a chance to look at one of the lesser-known ones.

The British publisher Ladybird made a series of four computer books, and while the first three had content for both the Sinclair Spectrum and the BBC Micro, the last in the series only featured the BBC. [Jason] took that book and re-imagined the missing Sinclair Spectrum version.

The surprise is how deep it dives into the architecture of an 8-bit computer, and it’s refreshing to see something that’s not unduly dumbed-down for kids. We’re guessing that this would have appealed to the 5% of kids who ran with their computers rather than just playing Jet Set Willy back then, and we’re sure a few grown-up 50-somethings may remember it or books like it.

If you think you may have seen Ladybird books here before, it may be because we reviewed another influential tech book of theirs for kids. Meanwhile you can take a look at the contemporary computer books from their arch-rival Usborne.