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Neville 24-09-2018 04:31 PM

IBM PCjr and Tandy 1000, the almost PC compatibles.
I already mentioned these two computers in a previous guide, but since many DOS games offer some kind of support for them, I think a more in-depth explanation could be of interest to the readers.

The IBM PCjr.

When IBM launched the first PC models around 1981, they had little in common with the PC clones we use these days. They employed MDA and CGA display cards, 8088 CPUs running at 4.77 Mhz and could have as little as 16 Kb. of RAM. Their prize was around $1.565 and they found success in office use, especially after the release of spreadsheet software.

By the end of 1983, IBM announced the PCjr. The PCjr was designed with the intention of becoming a home variant of the IBM PC, competing with other computers such as the Commodore 64, the Atari 8 bit family or the Apple II.

The PCjr would use the same CPU 8088 @ 4.77 Mhz of the IBM PC, but changes were made to the display and sound systems. The CGA display now supported several 16 color modes, and the PC speaker had three sound channels rather than one. The first "King's Quest" game by Sierra Online was ordered by IBM as an example of a game taking advantage of these extra features.

However, when the PCjr was finally released in 1984 it was poorly received. There are several reasons for that:

- It was competing with 8 bit computers, which were much cheaper than the PCjr, which sold at $669, and already had an stablished market.

- IBM had promised a fully PC compatible machine. However, with only 128 Kb. of RAM and limited expansion possibilities, many IBM PC programs wouldn't run in the PCjr.

- Accesories such as the wireless keyboard were widely criticised. Originally, the PCjr was shipped with a rubber keyboard that made typing at a reasonable speed almost impossible.

In 1985, IBM stopped manufacturing the PCjr after 250.000 units had been sold. IBM would not try to sell a home-oriented PC until the PS/1 in 1990.

IBM PCjr legacy and emulation.

Or the reason you may be interested in this system.

- Cartridge games: A handful of games were released in this format for the PCjr. Many of them were also released for DOS or in PC Booter format, but won't run in regular PCs.

- PC Booter games: These type of games were designed to run by booting the computer with their disks. This allowed for games to use different OSes than DOS or to implement their own copy protection schemes.

Some games from this era had either different CGA, PCjr and Tandy releases or are PCjr / Tandy exclusive, such as "Ghostbusters" or "Pitfall II". You may need an specific version to obtain PCjr benefits.

- Regular DOS games with PCjr support: This is the most common situation. A DOS game released during or after the PCjr era that has some kind of PCjr support. Normally this will mean plain CGA graphics, but some games such as "Pit Stop II" or "Super Boulder Dash" will show better graphics if they detect a PCjr machine.

"Super Boulder Dash" and "Montezuma's Revenge" in CGA and PCjr modes.

DOSBox can run PCjr software by setting machine=pcjr. It can also run PCjr cart dumps (files with a JRC extension) with the command BOOT name of file.JRC.

PCem offers one profile to run a PCjr machine, but doesn't support (yet) booting from a cartridge image.

Neville 24-09-2018 05:42 PM

The Tandy 1000.

The Tandy 1000 was an economic PC clone developed by Tandy Corporation and sold in their Radio Shack stores. It's hardly known outside the United States.

The first models were presented in november 1984. Since they were built around the IBM PCjr architecture and that computer was a flop, Tandy soon dropped any mention to the IBM PCjr. in their advertising. Early Tandy 1000 computers kept using the same components (CPU 8088 @ 4.77 MHZ, a CGA graphics adapter with some extra 16 color modes and a three-channel PC speaker) while newer models added a sound DAC, 80286 and 80386 CPUs and even VGA and SVGA graphic cards.

Many games from the era claim to be "Tandy compatible" or include mentions to "TGA Graphics".

The Tandy 1000 computers usually shipped with a customized version of DOS and Tandy Deskmate, a program environment. In many models the OS runs from ROM rather than from disk.

Tandy Deskmate v3.05.

In a way, the Tandy 1000 were what the PCjr should have been. They ignored the cartridge ports, added more RAM and made the computers easier to expand. Between this, the ubiquity of the Radio Shack stores and a prize of $1.200 (higher than the IBM PCjr, but lower than the rest of PC compatibles) the Tandy 1000 line of computers was successful until 1990, when the game developers started moving towards VGA graphics.

The last Tandy 1000 models were discontinued in 1993.

Tandy 1000 legacy and emulation.

Unlike the PCjr, there isn't much Tandy-specific software. Also consider that games designed for the PCjr won't necessarily run on a Tandy 1000. They are, after all, different systems.

On the other hand, given the popularity of the system many games before 1990 offer some kind of support for the Tandy 1000 or claim to be "Tandy compatible".

The lower spectrum of these games are those which, upon detecting a Tandy computer, will run in 16 color mode mode and little else. This is the case of "Secret of Monkey Island" or "Indiana Jones and the Last Crusade". These games were launched in 1989-90 in separate 16 and 256 color versions. Tandy 1000 users had to use the 16 color version.

"Indiana Jones and the Last Crusade" shows the same graphics under EGA and Tandy 1000 computers.

Other games will play better sound if a Tandy 1000 is detected. Better sound than a plain PC speaker, that is. That's the case of "Arkanoid" or many early Sierra Online games, such as "King's Quest" I to III, the first "Leisure Suit Larry" and the first two "Space Quest" games. All these make good use of the three channel PC speaker.

And finally, there are a few games with that acknowledge Tandy 1000 users with extras such as 16 color graphics (as opposed to plain CGA), different palettes and extra sounds.

A few of these are "Arcticfox", "Shangai" (which show 16 color graphics for Tandy users only), "Falcon" (which had an specific Tandy version), and "Outrun" (extra voices).

"Shanghai" and "Arctifox" running under CGA and Tandy modes.

As for emulation options, DOSBox is easily the best one. Use the setting machine=tandy and you are all set. Even the Tandy DAC of later models is emulated.

PCem also offer good Tandy emulation, but in this case you are limited to the models with 8088 and 8086 CPUs.


MobyGames list of PCjr cartridge games.

MobyGames list of games with PCjr / Tandy graphics support.

MobyGames list of games with PCjr / Tandy sound support.

MobyGames list of games with Tandy DAC sound support.

VOGONS thread about games with PCjr / Tandy support.

Nerdy Pleasures: IBM PCjr and Tandy 1000 games.

Neville 30-09-2018 02:16 PM

I've decided I'll use this thread to talk about peculiar PC machines I find about using emulation. My first PC was already 486/66 clone with SVGA graphics and a Sound Blaster, so I was a sort of late arrival to the PC world. Stuff like the CGA / Hercules wars or earlier PC clones are quite new to me.

And another thing: could anyone change the Tandy 100 bit in the title for Tandy 1000? It's a very embarrasing typo.

Neville 30-09-2018 02:48 PM

First of all, maybe I should explain why there are so many PC clones... see, when IBM made their first PC model (the 5150, released in august 1981) they built it using off the shelf components, and they also allowed other manufacturers to sell their own parts and peripherals. The only part that IBM kept copyrighted was the BIOS, imagining that other PC manufacturers would have to pay for it for years. Unfortunately for IBM, the PC BIOS was quickly reverse-engineered by brands like Compaq and American Megatrends.

Now, today I want to mention two Amstrad computers. The first is the Amstrad PC512 from 1986. Apparently it was very popular in Europe, to the extent this model and the 1640 may have been to Europe what the Tandy 1000 and variants were to the USA: the first affordable PC compatible for many people.

The specs are not too different from IBM PCs of the same era: 512 Kb. RAM, CPU 8086 @ 8 Mhz. and a CGA-compatible Amstrad graphics card, with an extra 640x200x16 graphic mode.

That extra graphic mode is the first curiosity. A few games claim to use it, such as "Maupiti Island" or "Frank Bruno's Boxing", but my guess is that it was especially included for use with the GEM desktop.

Maupiti Island, showing 16 colors.

The PC1512 came with three different startup disks. The first one, you guessed, was MS-DOS 3.2. The second one was a different DOS, DOS Plus, a DOS Variant developed by Digital Research and based on CP/M, an earlier OS shared by many 8 and 16 bit computers.

And the third disk was GEM, a variant of the desktop that was used in other computers at the time, most notably the Atari ST. This variant was also developed by Digital Research.

A PC1512 running GEM.

However GEM wasn't a big success in the PC market, and people soon moved to other software desktops, such as GS/OS, Deskmate and Windows.

The 1512 had a successor, the Amstrad PC1640, this time with 640 Kb. of RAM and an EGA compatible display card.

More rarities? Well, take a look at the pripherals on that first picture: the mouse (and I think the joystick as well) is not standard, but Amstrad's specific. It has a different connector and won't work unless you use the Amstrad drivers.

Well, at least you can emulate the whole thing using PCem.

The second Amstrad model I will mention this time is the Mega PC:

It's a PC compatible with a 386 CPU launched in 1993 lanzado en 1993. It's main appeal is that it has... a Sega Genesis / Mega Drive embedded. I can't possibly imagine who had the idea, but if you want a rare PC clone, you can't go much weirder than this one.

It's also a PC that brings me bad memories, because I accidentally destroyed one of them. I was in college at the time, and this machine was the one me and my friends we used to type our college works. I was told by the owner not to switch off the monitor (IIRC it was a custom one, the machine wouldn't work with regular PC monitors) because it was on its last legs. However, the computer crashed and out of habit I switched off both PC and monitor. From then on the monitor would only show a delicate violet light, but neither characters nor graphics. Damn.

The Mega PC likely didn't have much of an impact. By 1993 386-based PCs and the Sega Genesis / Mega Drive were likely at the end of their commercial lives.

PCem does emulate the machine, but only in regards to its PC side. For the Genesis / Mega Drive there are plenty of emulators to choose.

Smiling Spectre 01-10-2018 12:19 PM


Originally Posted by Neville (Post 482819)
And another thing: could anyone change the Tandy 100 bit in the title for Tandy 1000? It's a very embarrasing typo.

Can't author - you - do it? Hmm. Strange.

I renamed it for you.

Neville 01-10-2018 01:04 PM

I tried using the "advanced mode" and couldn't do it myself. Thank you.

Smiling Spectre 02-10-2018 06:18 AM

It's in Thread Tools - Moderation - Edit Thread. I thought, it's accessible for thread author. Seems, no. Ok.

And you are welcome.

Neville 07-10-2018 02:35 PM

Today I'm gonna talk about the IBM PS/1 line from 1990, and more especifically the 2121 model.

The IBM PS/1.

The first PS/1 model was the 2011, with a 80286 CPU @ 10 Mhz and VGA graphics. It was followed by models 2121, 2133 and 2155, with 386 and 486 CPUs. The PS/1 line was an attempt from IBM to re-conquer the domestic market, something IBM hadn't tried since the flop of the IBM PCjr in 1984.

I haven't found much information on if they were succesful or not, but since the line sold until 1994, when they were replaced by the Aptiva models, I deduce they were.

So, what is so great about this PCs? In my opinion, what makes them especial is the desktop IBM included with them. Is made up of four screens, and through the mouse the user can access several options, from an overview of the system to a tutorial, Microsoft Works and even several on-line services.

This desktop system is built over DOS 4.01 and may have been introduced as an answer to Tandy Deskmate or GEM. As we've seen, other computer manufacturers used those programs as "desktops" for their users.

In some PS/1 models, DOS was loaded from ROM, just as in the Tandy 1000 computers. This makes me think IBM had the Tandy 1000 competition in mind when they released the PS/1.

Another curiosity is that some PS/1 models didn't include ISA expansion slots. For those, IBM marketed a sound device, the PS/1 Audio Card.

It was, of all things, a three channel sound generator similar to the one provided with the IBM PCjr and the early Tandy 1000 computers. Depending on the source, the card could include a DAC for digital sounds. No need to mention, this was a rather outdated device by 1990. By that time both AdLib and Sound Blaster cards were widely available.


You can forget about using regular DOSBox in order to emulate the IBM PS/1, since it doesn't allow for specific computer models except for the IBM PCjr and the Tandy 1000.

However, you can use Ykhwong's DOSBox build, which does emulate the PS/1 Audio Card.

Here's a list of games with support for the PS/1 Audio Card.

If you want the full experience of using a PS/1, you will need to use PCem. And not only that, you'll need the system disks that came with every model. Without them, you'll get the four screens menu, but you will be prompted for a disk everytime you click on any of them.

Personally, I was able to find the system disks for the 2121 model, and that's what you are seeing on the captures.

Neville 07-10-2018 07:06 PM

This pretty much sums up my experience with PCs that weren't PC clones... if anybody wants to talk about specific computers they used and, if possible, give PC emulation tips, I think this is the thread to do it.

This also means I should have made up a better / more inviting title, but right now I can't think of any.

Rogue 16-10-2018 01:56 PM

I tried IBM's business OS - CP/M-86 and older versions of DOS on first couple of models. PCEM made it all possible. :OK:

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