8088

24 Articles

An IBM PC showing "68000 IBM PC" on its monitor

IBM PC Runs BASIC With Motorola 68000 CPU Upgrade

May 2, 2023 by 13 Comments

Although ARM CPUs have been making headway in several areas of computing over the last decade or so, the vast majority of desktop, laptop and server CPUs are still based on the x86 architecture. How that came to be is no secret, of course: IBM chose the Intel 8088 to power its model 5150 PC back in the early 1980s, and since it became the dominant PC platform, everyone else followed suit. But what if IBM’s purchasing department had got a good deal at Motorola instead? [Ted Fried] has been experimenting with that scenario, by equipping an IBM PC with a 68000 CPU.

To be fair, he didn’t use an actual Motorola chip; instead, he emulated a 68k core on a Teensy 4.1 and implemented the 8088’s bus interface on its pins. The emulated core does exactly the same thing an actual CPU would do, while the rest of the computer works the same way it always did – data is stored in the motherboard’s DRAM chips, keystrokes are processed by the standard 8255 chip and progam output is displayed on the monitor through the MDA video card. Continue reading “IBM PC Runs BASIC With Motorola 68000 CPU Upgrade” →

Wolfenstein 3D, As You Never Imagined It.

January 27, 2023 by 21 Comments

When tracing the history of first-person shooting (FPS) games, where do you credit with the genesis of the genre? Anyone who played 3D Monster Maze on the Sinclair ZX81 might dare to raise a hand, but we’re guessing that most of you will return to the early 1990s, and id Software. Their 1992 title Wolfenstein 3D might not have been the first to combine all the elements, but it’s arguably the first modern FPS and the first to gain huge popularity. Back in 1992 it needed at least a VGA card and a 286 to run, but here in 2023 [jhhoward] has taken it back a step further. You can now slay virtual Nazis in 3D on an 8088 PC equipped with a lowly CGA card.

Whether the gameplay survives in the sometimes-bizarre CGA color schemes and whether it becomes too pedestrian on an 8088 remains as an exercise for the reader to discover, but it’s a feat nevertheless. The textures all need converting to CGA mode before they can be used and there are even versions for the shareware and paid-for versions of the game.  It’s possible that an 8088 may never be able to say yes to “Will it run DOOM?”, but at least now it can run the predecessor.

Teensy Twofer Of Plug-In Emulated Retro CPUs

December 26, 2022 by 12 Comments

[Ted Fried] wrote in with not one but two (2!) new drop-in replacements for widespread old-school CPUs: the Zilog Z80 and the Intel 8088. Both of the “chips” run in cycle-accurate mode as well as in a super turbo mode, which can run so fast that you’ll need to use the Teensy’s internal RAM just to keep up.

Both of these designs have a hardware and software component. The PCBs basically adapt the pinout of the Teensy to the target CPU, with a bunch of 74VLC latches on board to do the voltage level conversion. The rest is a matter of emulating all of the instructions on the Teensy, which is more than fast enough to keep up. If this sounds familiar to you, it’s basically the same approach that [Ted] used last year to bring us his replacement for the 6502 found in the Apple ][ and Commodore 64.

Why would you want an emulated CPU when the originals are still available? [Ted] inherited a busted Osborne I, an ancient Z80 luggable. By replacing the original Z80 with his emulation, he could diagnose the entire system, which led him to discover some bad DRAM chips and get the old beast running again. Or maybe you just want to play IBM XT games at insane speeds?

And it looks like [Ted] has updated his 6502 emulation to include the undocumented C64 opcodes, so if you’re into that scene, you should be covered as well.

If any of this tickles your fancy, head over to [Ted]’s blog, microcore labs, and follow along. Although now that he’s covered most of the famous retrocomputers, we have to ask ourselves what processor is going to be next?

A Cycle-Accurate Intel 8088 Core For All Your Retro PC Needs

December 3, 2022 by 17 Comments

A problem faced increasingly by retrocomputer enthusiasts everywhere is the supply of chips. Once a piece of silicon goes out of production its demand can be supplied for a time by old stock and second hand parts, but as they become rare so the cost of what can be dubious parts accelerates out of reach. Happily for CPUs at least, there’s a ray of hope in the form of FPGA-based cores which can replace the real thing, and for early PC owners there’s a new one from [Ted Fried]. MCL86 is a cycle accurate Intel 8088 FPGA Core that can be used within an FPGA design or as a standalone in-circuit replacement for a real 8088. It even has a full-speed mode that sacrifices cycle accuracy and can accelerate those 8088 instructions by 400%.

Reading the posts on his blog, it’s clear that this is a capable design, and it’s even been extended with a mode that adds cache RAM to mirror the system memory at the processor’s speed. You can find all the code in a GitHub repository should you be curious enough to investigate for yourself. We’ve pondered in the past where the x86 single board computers are, perhaps it could be projects like this that provide some of them.

Bringing Up An Old Motherboard Is A Delicate Process

November 12, 2022 by 12 Comments

If you were around for the early days of the personal computer revolution, you’ll no doubt recall the excitement every time IBM announced a new version of its beige boxes. For a lot of us, the excitement was purely vicarious, for despite the “personal” moniker, mere mortals could rarely afford a branded IBM machine. But it was still cool to keep track of the latest releases, and dream of the days when cheap clones would make it possible to play.

[Anders Nielsen]’s recent find of an original IBM Model 5160 motherboard sort of echoes that long-ago excitement, but in a different way. This board, from a PC XT built in 1984, was in unknown condition upon arrival, so [Anders] set about a careful process to try to bring the board back to life. A quick visual inspection leaves one with a sense of both how much things have changed, and how much they’ve stayed the same. Aside from the big 40-pin DIP 8088 CPU and the BIOS ROMs, the board is almost completely populated with discrete logic chips, but at the same time, the basic footprint of a motherboard has changed very little.

The bring-up process in the video below includes checks of all the power rails for shorts, which ended up being a good call — drat those tantalums. After fixing that issue, [Anders] had a bit of trouble getting the board to POST, and eventually resorted to dumping the BIOS ROMs and inspecting the contents. One of the chips had picked up a case of the scramblies at some point, which was easy enough to fix thanks to images of the 5160 ROMs available online. We thought the trick of using a 64k ROM and just writing the BIOS image twice was pretty clever.

In the end, the board came up, although without video or keyboard — that’s for another day. Can’t find your own PC XT motherboard to play with? Then maybe you can just build one.

Continue reading “Bringing Up An Old Motherboard Is A Delicate Process” →

Building Your Own 8088 XT Motherboard

May 21, 2022 by 47 Comments

There was a time when an XT-class motherboard — like the old IBM PC with an 8088 CPU — was a high-tech accomplishment. Now, something like that is easily within reach of the average hobby lab. [Homebrew8088] did it, and it looks surprisingly simple, especially compared to what passes for a motherboard these days.

The board will take an 8088 or one of the NEC chips and by default sports 512 K of RAM, a few ISA slots, a PC speaker, a USB hard drive, and a PS/2 keyboard connector. The board will fit in an ATX case. Not bad. You can see a video of the board below.

In fact, the channel has a lot of related videos and the main site has many interesting topics, like driving an 8088 or 8086 from a Raspberry Pi. The GitHub site has design files for KiCad along with a lot of other information. Some of this will be interesting even if you are just trying to repair an old motherboard or would like to design a new ISA card.

If you want to know why the PC used an 8088 instead of an 8086, we just covered that. What are you going to do with an old XT computer? How about IRC?

Continue reading “Building Your Own 8088 XT Motherboard” →

How The IBM PC Went 8-Bit

May 17, 2022 by 52 Comments

If you were around when the IBM PC rolled out, two things probably caught you by surprise. One is that the company that made the Selectric put that ridiculous keyboard on it. The other was that it had an 8-bit CPU onboard.  It was actually even stranger than that. The PC sported an 8088 which was a 16-bit 8086 stripped down to an 8 bit external bus. You have to wonder what caused that, and [Steven Leibson] has a great post that explains what went down all those years ago.

Before the IBM PC, nearly all personal computers were 8-bit and had 16-bit address buses. Although 64K may have seemed enough for anyone, many realized that was going to be a brick wall fairly soon. So the answer was larger address buses and addressing modes.

Intel knew this and was working on the flagship iAPX 432. This was going to represent a radical departure from the 8080-series CPUs designed from the start for high-level languages like Ada. However, the radical design took longer than expected. The project started in 1976 but wouldn’t see the light of day until 1981. It was clear they needed something sooner, so the 8086 — a 16-bit processor clearly derived from the 8080 was born. Continue reading “How The IBM PC Went 8-Bit” →