DEC

30 Articles

Booting A Desktop PDP-11

March 23, 2025 by 22 Comments

Ever heard of VENIX? There were lots of variants of Unix back in the day, and VENIX was one for the DEC Professional 380, which was — sort of — a PDP 11. The 1982 machine normally ran the unfortunately (but perhaps aptly) named P/OS, but you could get VENIX, too. [OldVCR] wanted to put one of these back online and decided the ST-506 hard drive was too risky. A solid-state drive upgrade and doubling the RAM to a whole megabyte was the plan.

It might seem funny to think of a desktop workstation that was essentially a PDP-11 minicomputer, but in the rush to corner the personal computer market, many vendors did the same thing: shrinking their legacy CPUs. DEC had a spotty history with small computers. [Ken Olsen] didn’t think anyone would ever want a personal computer, and the salespeople feared that cheap computers would eat into traditional sales. The Professional 350 was born out of DEC’s efforts to catch up, as [OldVCR] explains. He grabbed this one from a storage unit about to be emptied for scrap.

The post is very long, but you get a lot of history and a great look inside this vintage machine. Of course, the PDP-11 couldn’t actually handle more than 64K without tricks and you’ll learn more about that towards the end of the post, too.

Just as a preview, the story has a happy ending, including a surprising expression of gratitude from the aging computer. DEC didn’t enjoy much success in the small computer arena, eventually being bought by Compaq, which, in turn, was bought by Dell HP. During their heyday, this would have been unthinkable.

The PDP/11 did have some success because it was put on a chip that ended up in several lower-end machines, like the Heathkit H11. Ever wonder how people programmed the PDP computers with switches and lights?

UNIX Archaeology Turns Up 1972 “V2 Beta”

February 20, 2025 by 20 Comments

In 1997 a set of DEC tapes were provided by Dennis Ritchie, as historical artifacts for those interested in the gestation of the UNIX operating system. The resulting archive files have recently been analysed by [Yfeng Gao], who has succeeded in recovering a working UNIX version from 1972. What makes it particularly interesting is that this is not a released version, instead it’s a work in progress sitting somewhere between versions 1 and 2. He’s therefore taken the liberty of naming it “V2 Beta”.

If you happen to have a PDP-11/20 you should be able to run this operating system for yourself, and for those of us without he’s provided information on which emulator will work. The interesting information for us comes in the README accompanying the tapes themselves, and in those accompanying the analysis. Aside from file fragments left over from previous users of the same tape, we learn about the state of UNIX time in 1972. This dates from the period when increments were in sixtieths of a second due to the ease of using the mains power frequency in a PDP, so with a 32-bit counter they were facing imminent roll-over. The 1970-01-01 epoch and one second increments would be adopted later in the year, but meanwhile this is an unusual curio.

If you manage to run this OS, and especially if you find anything further in the files, we’d love to hear. Meanwhile, this is not the oldest UNIX out there.

Featured image: “PDP-11/20 Rocker Switches” by Don DeBold

Your VAX In A Cloud Is Ready

January 28, 2025 by 16 Comments

For many people of a certain age, the DEC VAX was the first computer they ever used. They were everywhere, powerful for their day, and relatively affordable for schools and businesses. These minicomputers were smaller than the mainframes of their day, but bigger than what we think of as a computer today. So even if you could find an old one in working order, it would be a lot more trouble than refurbishing, say, an old Commodore 64. But if you want to play on a VAX, you might want to get a free membership on DECUServe, a service that will let you remotely access a VAX in all its glory.

The machine is set up as a system of conferences organized in notebooks. However, you do wind up at a perfectly fine VAX prompt (OpenVMS).

Continue reading “Your VAX In A Cloud Is Ready” →

A Look At The DEC VT220, A Proper Serial Terminal

July 17, 2024 by 52 Comments

If you’re reading Hackaday, we’re willing to bet that if somebody asked you about a serial terminal, you’d immediately think about a piece of software — a tool you run on the computer to communicate with some hardware gadget over UART. You might even have a favorite one, perhaps minicom or tio. You’d be technically correct (which we all know is the best kind of correct), but if you wind back the clock a bit, there’s a little more to the story.

You see, the programs we use these days to talk to microcontrollers and routers are more accurately referred to as serial terminal emulators, because they are doing in software what used to be the job of hardware. What kind of hardware? Why beauties like this DEC VT220 for example.

Continue reading “A Look At The DEC VT220, A Proper Serial Terminal” →

The Workstation You Wanted In 1990, In Your Pocket

July 3, 2024 by 59 Comments

Years ago there was a sharp divide in desktop computing between the mundane PC-type machines, and the so-called workstations which were the UNIX powerhouses of the day. A lot of familiar names produced these high-end systems, including the king of the minicomputer world, DEC. The late-80s version of their DECstation line had a MIPS processor, and ran ULTRIX and DECWindows, their versions of UNIX and X respectively. When we used one back in the day it was a very high-end machine, but now as [rscott2049] shows us, it can be emulated on an RP2040 microcontroller.

On the business card sized board is an RP2040, 32 MB of PSRAM, an Ethernet interface, and a VGA socket. The keyboard and mouse are USB. It drives a monochrome screen at 1024 x 864 pixels, which would have been quite something over three decades ago.

It’s difficult to communicate how powerful a machine like this felt back in the very early 1990s, when by today’s standards it seems laughably low-spec. It’s worth remembering though that the software of the day was much less demanding and lacking in bloat. We’d be interested to see whether this could be used as an X server to display a more up-to-date application on another machine, for at least an illusion of a modern web browser loading Hackaday on DECWindows.

Full details of the project can be found in its GitHub repository.

How DEC’s LANBridge 100 Gave Ethernet A Fighting Chance

April 9, 2024 by 17 Comments
Alan Kirby (left) and Mark Kempf with the LANBridge 100, serial number 0001. (Credit: Alan Kirby)
Alan Kirby (left) and Mark Kempf with the LANBridge 100, serial number 0001. (Credit: Alan Kirby)

When Ethernet was originally envisioned, it would use a common, shared medium (the ‘Ether’ part), with transmitting and collision resolution handled by the carrier sense multiple access with collision detection (CSMA/CD) method. While effective and cheap, this limited Ethernet to a 1.5 km cable run and 10 Mb/s transfer rate. As [Alan Kirby] worked at Digital Equipment Corp. (DEC) in the 1980s and 1990s, he saw how competing network technologies including Fiber Distributed Data Interface (FDDI) – that DEC also worked on – threatened to extinguish Ethernet despite these alternatives being more expensive. The solution here would be store-and-forward switching, [Alan] figured.

After teaming up with Mark Kempf, both engineers managed to convince DEC management to give them a chance to develop such a switch for Ethernet, which turned into the LANBridge 100. As a so-called ‘learning bridge’, it operated on Layer 2 of the network stack, learning the MAC addresses of the connected systems and forwarding only those packets that were relevant for the other network. This instantly prevented collisions between thus connected networks, allowed for long (fiber) runs between bridges and would be the beginning of the transformation of Ethernet as a shared medium (like WiFi today) into a star topology network, with each connected system getting its very own Ethernet cable to a dedicated switch port.

PDP-10 Fits In Your Living Room

March 13, 2024 by 8 Comments

[Oscar] at Obsolescence Guaranteed is well-known for fun replicas of the PDP-8 and PDP-11 using the Raspberry Pi (along with some other simulated vintage computers). His latest attempt is the PDP-10, and you can see how it looks in the demo video below.

Watching the video will remind you of every old movie or TV show you’ve ever seen with a computer, complete with typing noise. The PDP-10, also known as a DECsystem-10, was a mainframe computer that usually ran TOPS-10. These were technically “mainframes” in 1966, although the VAX eclipsed the system. By 1983 (the end of the PDP-10’s run), around 1,500 had been sold, including ones that ran at Harvard, Stanford, Carnegie Mellon, and — of course — MIT. They also found homes at CompuServe and Tymshare.

The original 36-bit machine used transistors and was relatively slow. By the 1970s, newer variants used ICs or ECL and gained some speed. A cheap version using the AM2901 bit-slice CPU and a familiar 8080 controlling the system showed up in 1978 and billed itself as “the world’s lowest cost mainframe.”

The Knight terminals were very unusual for the day. They each used a PDP-11 and had impressive graphics capability compared to similar devices from the early 1970s. You can see some of that in the demo video.

Naturally, anyone who used a PDP-10 would think a Raspberry Pi was a supercomputer, and they wouldn’t be wrong. Still, these machines were the launching pad for Adventure, Zork, and Altair Basic, which spawned Microsoft.

The cheap version of these used bitslice which we’ve been talking about lately. [Oscar] is also known for the KIMUno, which we converted into a COSMAC Elf.