Making Intel Mad, Retrocomputing Edition

June 9, 2024 by Bryan Cockfield 20 Comments

Intel has had a deathgrip on the PC world since the standardization around the software and hardware available on IBM boxes in the 90s. And if you think you’re free of them because you have an AMD chip, that’s just Intel’s instruction set with a different badge on the silicon. At least AMD licenses it, though — in the 80s there was another game in town that didn’t exactly ask for permission before implementing, and improving upon, the Intel chips available at the time.

The NEC V20 CPU was a chip that was a drop-in replacement for the Intel 8088 and made some performance improvements to it as well. Even though the 186 and 286 were available at the time of its release, this was an era before planned obsolescence as a business model was king so there were plenty of 8088 systems still working and relevant that could take advantage of this upgrade. In fact, the V20 was able to implement some of the improved instructions from these more modern chips. And this wasn’t an expensive upgrade either, with kits starting around $16 at the time which is about $50 today, adjusting for inflation.

This deep dive into the V20 isn’t limited to a history lesson and technological discussion, though. There’s also a project based on Arduino which makes use of the 8088 with some upgrades to support the NEC V20 and a test suite for a V20 emulator as well.

If you had an original IBM with one of these chips, though, things weren’t all smooth sailing for this straightforward upgrade at the time. A years-long legal battle ensued over the contents of the V20 microcode and whether or not it constituted copyright infringement. Intel was able to drag the process out long enough that by the time the lawsuit settled, the chips were relatively obsolete, leaving the NEC V20 to sit firmly in retrocomputing (and legal) history.

The Book8088 Gets A Post-Hype Review

February 22, 2024 by Jenny List 24 Comments

Last year, a couple of rather unusual computers emerged from China: a 386sx-based palmtop and an 8088-based mini-laptop. The average person isn’t exactly clamoring for a DOS machine these days, but they attracted quite a bit of interest among the retrocomputing scene. Now the dust has settled, [The Retro Shack] has taken a Book 8088 and given it an honest review. Do you need portable 1980s computing in your life, and if so it this the machine to give you it?

The first impression of the machine is just how svelte it is, being like a small but chunky netbook. He explores the hardware and finds as expected an NEC V20 instead of the Intel part running the show, and what would have been a hugely expanded DOS PC back in the day with its VGA and sound card, not to mention a solid state hard drive.

We’re overcome with a bit of nostalgia here at the sight of DOS running Lemmings, and on a machine we’d have given anything to own back in the 1980s. His final conclusion is that it’s a very nice little PC but around $160 seems a little much for what is essentially a toy. We have sadly to agree with him though we really want one, though noting that such a machine would have retailed for a huge amount more than that in 1980s dollars and we’d have considered it a huge bargain then.

If you’re still curious, we covered the arrival of these machines last year.

Continue reading “The Book8088 Gets A Post-Hype Review” →

Finally, An Open-Source 8088 BIOS

October 20, 2023 by Lewin Day 7 Comments

The Intel 8088 is an interesting chip, being a variant of the more well-known 8086. Given the latter went on to lend its designation to one of the world’s favorite architectures, you can tell which of the two was higher status. Regardless, it was the 8088 that lived in the first IBM PC, and now, it even has its own open-source BIOS.

As with any BIOS, or Basic Input Output System, it’s charged with handling core low-level features for computers like the Micro 8088, Xi 8088, and NuXT. It handles chipset identification, keyboard and mouse communication, real-time clock, and display initialization, among other things.

Of course, BIOSes for 8088-based machines already exist. However, in many cases, they are considered to be proprietary code that cannot be freely shared over the internet. For retrocomputing enthusiasts, it’s of great value to have a open-source BIOS that can be shared, modified, and tweaked as needed to suit a wide variety of end uses.

If you want to learn more about the 8088 CPU, we’ve looked in depth at that topic before. Feel free to drop us a line with your own retro Intel hacks if you’ve got them kicking around!

Decoding The 8088

October 9, 2023 by Al Williams 2 Comments

There is a lot to like about open software, and in some areas, a well-thought-out piece of software can really make a huge impact. A great example of this is the Sigrok project. Creating simple devices that act like a logic analyzer is relatively easy. What’s hard is writing nice software for such a setup including protocol decoders. Sigrok has done it and since it is open, you can add your device and decode your protocol. [GloriousCow] had done the hardware part of interfacing to the 8088 in an IBM PC using an off-the-shelf logic analyzer that uses a customized version of Sigrok. But the output was a CSV file you had to process in a spreadsheet program. The next step: write a decoder for Sigrok to understand 8088 bus cycles.

The post covers the details of writing such a plug-in for Pulseview, the Sigrok GUI. It will also work for the command line interface if you prefer that. The code is in Python.

Continue reading “Decoding The 8088” →

Bus Sniffing The Model 5150 For Better Emulation

October 3, 2023 by Dan Maloney 6 Comments

At the risk of stating the obvious, a PC is more than just its processor. And if you want to accurately emulate what’s going on inside the CPU, you’d do well to pay attention to the rest of the machine, as [GloriousCow] shows us by bus-sniffing the original IBM Model 5150.

A little background is perhaps in order. Earlier this year, [GloriousCow] revealed MartyPC, the cycle-accurate 8088 emulator written entirely in Rust. A cycle-accurate emulation of the original IBM PC is perhaps a bit overkill, unless of course you need to run something like Area 5150, a demo that stretches what’s possible with the original PC architecture but is notoriously finicky about what hardware it runs on.

Getting Area 5150 running on an emulator wasn’t enough for [GloriousCow], though, so a deep dive into exactly what’s happening on the bus of an original IBM Model 5150 was in order. After toying with and wisely dismissing several homebrew logic analyzer solutions, a DSLogic U3Pro32 logic analyzer was drafted into the project.

Fitting the probes for the 32-channel instrument could have been a problem except for the rarely populated socket for the 8087 floating-point coprocessor on the motherboard. A custom adapter gave access to most of the interesting lines, including address and data buses, while a few more signals, like the CGA sync lines, were tapped directly off the video card.

Capturing one second of operation yielded a whopping 1.48 GB CSV file, but a little massaging with Python trimmed the file considerably. That’s when the real fun began, strangely enough in Excel, which [GloriousCow] used as an ad hoc but quite effective visualization tool, thanks to the clever use of custom formatting. We especially like the column that shows low-to-high transitions as a square wave — going down the column, sure, but still really useful.

The whole thing is a powerful toolkit for exploring the action on the bus during the execution of Area 5150, only part of which [GloriousCow] has undertaken as yet. We’ll be eagerly awaiting the next steps on this one — maybe it’ll even help get the demo running as well as 8088MPH on a modded Book8088.

Book8088 Slows Down To Join The Demoscene

September 12, 2023 by Dan Maloney 9 Comments

As obsolete as the original IBM Model 5150 PC may appear, it’s pretty much the proverbial giant’s shoulders upon which we all stand today. That makes the machine worth celebrating, so much so that we now have machines like the Book8088, a diminutive clamshell-style machine made from period-correct PC chips; sort of a “netbook that never was.”

But the Book8088 only approximates the original specs of the IBM PC, making some clever hardware hacks necessary to run some of the more specialized software that has since been developed to really stretch the limits of the architecture. [GloriousCow]’s first steps were to replace the Book8088’s CPU, an NEC V20, with an actual 8088, and the display controller with a CGA-accurate Motorola MC6845. Neither of these quite did the trick, though, at least not on the demanding 8088MPH demo, which makes assumptions about CPU speed based on the quirky DRAM refresh scheme used in the original IBM PC.

Knowing this, [GloriousCow] embarked on a bodge-fest aimed at convincing the demo that the slightly overclocked Book8088 was really just a 4.77-MHz machine with a CGA adapter. This involved cutting a trace on the DMA controller and reconnecting it to the machine’s ~~PIO~~ timer chip, with the help of a 74LS74 flip-flop, a chip that made an appearance in the 5150 but was omitted from the Book8088. Thankfully, the netbook has plenty of room for these mods, and with the addition of a little bit of assembly code, the netbook was able to convince 8088MPH that it was running on the correct hardware.

We thoroughly enjoyed this trip down the DMA/DRAM rabbit hole. The work isn’t finished yet, though — the throttled netbook still won’t run the Area 5150 demo yet. Given [GloriousCow]’s recent Rust-based cycle-accurate PC emulation, we feel pretty good that this will come to pass soon enough.

Will An 8088 Run DOOM? Now, Yes It Will!

September 2, 2023 by Jenny List 12 Comments

The question on everyone’s lips when a new piece of hardware comes out is this: Will it run DOOM? Many pieces of modern hardware have been coaxed into playing id Software’s 1993 classic, but there have always been some older machines that just didn’t have the power to do it. One of them has now been conquered though, and it’s a doozy. [Frenkel]’s Doom8088, as its name suggests, is a port of the game for the original PC and AT.

As can be seen in this gameplay video, it’s not always the slickest of gaming experiences. But it works, so the question is, how on earth can a machine that was below the spec of the original, run this game? The answer comes in it being a port of GBADoom for the Game Boy Advance, a platform with less memory than a DOS PC. It still relies on extensive hard disk access for every frame though, which leaves it snail-like.

We set out to install it ourselves on one of the web based PC emulators, but fell over on the size of the required Watcom installation. If any of you have the real thing lying around though, we’d love to hear about how the game performed in the comments.

We’ve shown you so many ports of DOOM over the years to have lost count. One of our favourite recent ones uses an extremely unconventional but very retro display.