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- Опубликовано: 6 окт 2024
- Dave looks at the biggest flop in 1980's personal computers, the IBM PC Jr.
Teardown and extensive walk-through of the main motherboard.
Part 2: Troubleshooting - • EEVblog 1053 - Part 2 ...
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I live in Marietta, Ga! And thats the number for our local Micro Center (US computer outlet)
I worked at IBM at the time the PC Jr came out and it was obvious to anyone with more than a single functioning brain cell that the idea behind it was ... insane. IBM had no concept of how to sell to individual consumers though they were masters at the corporate market. The management at IBM was so outclassed by Bill Gates and others that as an IBM employee it was actually quite depressing. In the late 80's or early 90's a reporter asked Gates about IBM and Gates quipped that "... IBM was irrelevant ...". Much as I hated it Gates was right.
The original PC was pioneering but even then Gates held the keys to the kingdom. The PS/2 tried to gain greater proprietary control with the microchannel and the development of graphics which, for about the first time, permitted reasonable viewing of digital images. It never took off as the industry had by then figured out they could cut IBM out of the deal and take control of the standards so the PS/2 and microchannel never achieved the control IBM hoped for.
In the end Bill Gates nailed IBM to the cross and IBM was there greatest ally in accomplishing that.
I would have to agree with you. I don't believe that IBM ever "really" wanted to be in the home market. They really underestimated the market share that was available. The biggest drawback had ALWAYS been the arrogance of proprietary design. As far as "ole Bill" is concerned, he was a law school dropout. The ONLY thing "He" actually invented for the computer market that was truly successful was the EULA, and even THAT became an industry standard copied by all others. Anything else he got he either stole or copied, because, you know, legal. His initial licensing with IBM is the ONLY thing that got him the clout he needed to be a successful player in the computer industry.
Raptorman0909 my grandfather had ordered one of these through some program ibm had for employees.
That sponge did hold up quite well with time :D
First time watching this channel and I quite like you! From the enthusiasm in your voice to the easy to understand explanations of how the mainboard works without getting too hung up on every last pin.
Dave, open up the memory expansion side thing. The upgrade to 512Kb should be full of wires going everywhere. I remember upgrading mine. The plans for the upgrade came on fan fold paper. Of course, all ascii art. We were amazed to have a PC with 640 k at that time.
Will do, forgot that!
Your user icon is my image :-P
Yes, it is!! I had it for years now... The "dancing dolls" never get old.
If you can check to see if the cartdrige reboot system is as I comment below..
We used to make the weired connectors for the back ourselves with standard headders. You should have seen IBM's printer cable. Built like a tank..
Have you seen/touched an IBM PC JX? My uncle did contract work for IBM in Boca in the 80s, and brought home a prototype of the machine. The thing was gorgeous. It's what the PC Jr should have been. I'm surprised you didn't mention it, since it was also for the Aussie market. Cheers!
WTF? The most intresting Part is this modded Memory Expansion! So please tear this down!
You can find instructions on the web about how to do the mod (as well as tons of other PCjr mods, like overclocking, two floppy drives, making the PCjr video mode Tandy-compatible, etc.).
In fact, I went ahead and uploaded the file I have here: mkgraham.dx.am/pcjr.html
Download the PCjr Club Library file and look in the Tool Box folder for a ton of mod instructions. I just realized it doesn't include 512k instructions for the IBM sidecars, but it has 256k and 384k upgrade instructions, and has larger upgrade instructions for the Racore sidecars (and I somehow adapted them for the Microsoft Booster sidecar at one point in time).
This was my first PC and I loved it. First exposure to command-line DOS and hours of typing in BASIC code from the magazines of the day. More hours with Hitchhiker's Guide and Zork. Then the first Kings Quest brought graphics. After adding the 640kb memory upgrade it ran the first Test Drive. Fond memories of the PCjr.
My 2nd computer was a PCjr ( first was zx81 ), w/256K. It was a very capable word priocessor for me. It even had the speech synthesizer expansion card. In total there were 4 expansion cards attached, made it look like it was growing up!
Crikey, I remember these things at school... just horrible... just HORRIBLE. Always was seeking out the NEC V30 based machine instead.
4.77 MHz was standard across the entire PC lineup. They chose that instead of the rated 5 MHz because it was a convenient frequency for the CGA to generate its clock and color burst frequencies from. They cut a few KHz off the chip's top speed to avoid having to put another oscillator in an addon card.
Thats what he said
My Mom bought this for me back in the day with 128K and the updated wireless keyboard and the dot matrix printer. It was the greatest thing ever for me. Kings Quest was unreal. then I begged for the 256K sidecar upgrade. I used that all the way to college as nothing more than a word processor. I now have another PCjr since the original died. Man....with all the quirks I still LOVE this system.
Saved an IBM 8513 CRT awhile back, grabbed it off the side of the road.
I remember using that back in the 80's. You're probably right around my age(45) or a little older.
"The biggest 80's computer fail" *cries in DEC Rainbow*
Some companies did add a second oscillator for 8 MHz and called it the TURBO mode. Amazingly, they actually had a button to choose TURBO mode, instead of running it at 8 MHz all the time...
ats89117 The turbo button was nessecary because a lot of software, mostly games, was timing sensitive and would run to fast at the higher clock frequency. Standard speed was 4.77MHz.
Yeah.. try to run one of those old games in a DOS window today.. :-) It'll be game over before you get your finger off of the start button!!
Steve Jones , thats were dosbox and slowdown.exe come in handy! 😴😉
That adapter cable will last until the Sun goes nova.
The statement was meant to be taken as hyperbole. However, the Sun is massive enough to become a red giant, and will throw off a planetary nebula before transitioning into a white dwarfs. The word nova means new star and often refers to this phase of stellar transition.
Thanks for the support. He's correct that in-falling hydrogen on white dwarf is called a nova, but he doesn't understand that nova is catch all term. It is used anytime a star undergoes a massive change in brightness. I didn't bother replying because I've seen how debates on the internet go.
Actually that's not true and he's right, to be called nova a star must grow its brightness in a very short time so slowly becoming a red giant does not qualify.
ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/supernovae.htm
Note that they state most nova are the result of accretion onto a white dwarf. Stars as massive as the Sun can experience a ‘helium flash’ which takes place in a matter of minutes to hours. The PBS Space Time RUclips channel just had a video about this topic. ruclips.net/video/iJY3y5_k0do/видео.html
"Note that they state most nova are the result of accretion onto a white dwarf"
Eh. That requires a binary system and the sun is all alone, so that can't happen and the sun can't turn itself into a nova, which I believe has been the point of this whole thread.
" Stars as massive as the Sun can experience a ‘helium flash’ "
Yes, but what it has to do wit a nova ? The name "flash" maybe is suggesting something like a camera's flash, in reality almost all the energy goes into the expansion of the core (which happens very fast, like an explosion) but the flash happens there and it's not directly observable from outside.
If you were looking at a read giant while the helium flash is occurring, you wouldn't notice anything.
Hey Dave, when using old clips you should make sure to look at the audio track because quite often old stuff is mono, not stereo.
I'm sure you know it's an easy fix and the audio at 4:40 was just an oversight.
Love the videos Dave, have a good one.
Tandy did a much better job of taking the PC Jr tech and turning it into a usable product with the Tandy 1000.
Indeed
ruclips.net/video/av5NQ_3mW9A/видео.html
Are you the same tandy ?
@Rohit Chaturvedi, Not quite, the original Tandy Corporation AKA RadioShack went bankrupt. We acquired some of the company assets including the Tandy brand and have revived it.
1000EX was my first!
One thing about Tandy computers, they seemed to be well built. I worked at radio shack during my college years and we had a 386 Tandy come back for routine service because the floppy wouldn't read data anymore. It was used in a farming equipment service center... or maybe they used it as the plow. It didn't look too bad on the outside, but when we opened it; it was almost completely full of dirt. You could not see any part of the motherboard. It looked like the surface of the moon. There would be a little square or rectangular rise in the dust where a chip was. Not one colored wire or piece of green PCB anywhere to be seen. Cleaned it out, cleaned the heads on the floppy.... good to go. I realize older computers didn't suffer from thermal issues like the modern counterparts, but to see a computer almost completely full of dirt and in regular service is something to behold.
I love your "HI" at the beginning of the videos you do.
I already knew the PC Jr. was a train wreck of a machine, but I had no idea that it had so many bizarre proprietary ports on the back.
I built my own 128K side car expansion. Designed the Refresh logic and eteched the PCB. I was lucky to find the source of the funky sidecar pass thru connectors. Also built a sidecar that accepted an ISA hard drive adapter card. Had to reprogram the bios on hard drive controller card to use polling mode since no DMA controller. Had to de-compile/assemble the controller bios to source code (it was not published as far as i know) and hack in the polling code. Connected an Oveletti 8MB hard drive. I was in heaven.
Had great fun designing and building those projects, learned quite a lot.
Jeez, this really brings back some memories, Dave! This is pretty much how far back you have to go to see 74LSxx logic on consumer products.
The video appeared in my feed with the Jr. truncated, and I thought this was going to be about how the IBM PC was the biggest failure of the 80s.
I was confused and excited to see why you thought that the single most successful platform was actually a huge piece of crap. I'm not sure if I'm disappointed or relieved.
+Christopher Pilcher yeah, the problem with long titles!
Ironically the Tandy 1000 was a clone of it. And it was one of Tandy's most successful product.
Mentioned in there
Nice. Still watching it. Great video!
One of the main reasons was that it used standard components and connectors, not these stupid proprietary IBM ones.
Actually, the Tandy 1000 was not exactly a clone. First, it had much higher end graphics onboard. Second, it was based on the Phoenix BIOS. Third, it had more address space due to some odd little choices made with regards to DMA allocation. Fourth, it actually had a multi voice audio controller. Fifth, it came standard with joystick ports and controllers. Sixth, it supported MFM hard drives directly on board. Seventh, it actually had a dual mode switching power supply. 8, It ran IBM DOS directly with zero mods. 9th it had the ability to run IBM Basic, natively. The Tandy 1000 was much more than a clone. It was the machine the 5150 should have been. Having said all of that, actually, the Tandy 2000 was Radio Shack/Tandy Corps most successful machine. Yes it had compatibility issues but, it was faster and far more capable than anything IBM and ALL other clones had to offer at the time. And, featured what would become industry standard over time, video mapped outside the system RAM space.
Radio Shack managed to clean up fine over IBM's mess.
The encoder on the floppy drive is designed so that you can adjust the speed from the 50/60hz flicker from a fluorescent light
Ah, yes, instant timing light!
Good call, over engineering knocked down to the bulb in the factory!
The ADC with a NE555 timer is classic and nicely thought out. They sometimes even used it as a kind of DAC back than.
I had one of the original IBM PCs and a PC Jr, both were useless.
This was my very first family computer. My dad got it from IBM before he left his job there, when I was a toddler
That tidy motherboard design and assembly job brought to you by automated insertion and wave soldering ;-)
By this I was working on IBM PC's and had built my own clone, and could not believe how bad jr was.
I could be wrong but I seem to remember a journalist describing using the original keyboard describing it as like "typing on porridge".
IBM always sucked at marketing......they made great stuff, but couldn't seem to get their head out of their ass......
The Charlie Chaplan campaign was very successful.
No one ever got fired for buying IBM.
Charlie Chaplin
Jeremy Dixon I agree....they were great marketing to business, but during the "Big Iron" days there wasn't a whole lot of competition. Once micro and mini PC's really took off, they nearly went into bankruptcy in the early 90's
Back in the 1970's one of my coworkers was deciding on what mainframe the business should purchase. He told the IBM salesman that a 370 would be too expensive and he was considering a DEC System 10. The salesman called his boss and told him that his employee was showing signs of a mental breakdown and should be sent for counseling before given any more responsibilities!
I think I remember that commercial - a shorter version of it anyway.
nope, it was the Digital Equipment Corp. entry into personal computer business. It never went anywhere. Legend has it that Ken Olson got fed up with the technical issues with it, called in the lead engineer in his office, showed him an opened machine and all the eco wires on the main board, asked "What the hell is that?!" and fired him on the spot!
36:22 that's /dev/null
The PCJr may have been ridiculous, but it was where I got my start at 6yrs old or so and it started my love of computing and electronics. DOS 2.1, Cartridge
Basic, Microsoft Adventure (xyzzy!), 2-channel PC speaker, and BASIC programs printed in the back of Sky and Telescope magazine.
"They don't like tying themselves to one manufacturer"
Yep, ThinkPad keyboards from 2-4 different manufacturers (the number depends on the type of ThinkPad).
That has to be the most used PCjr I've ever seen in my life. I've never seen one so filthy from use or even with all of those sidecars. Someone really loved that thing at one time in its life.
Ahhhh, the Peanut. That's what we called it. Was sold at IBM's short-lived retail outlets, typically located in the parking lots of shopping malls, usually sold to banks for use as satellite branches.
Dave, the extra power module was typically not needed. Very few of those were sold. But it was necessary if you loaded up the PCjr with "wedges", like that printer port wedge you showed.
As for why the Jr was so lean.... the idea was to use the Peanut to get folks thinking about upgrading to an XT and the execs did not want Peanut cutting into XT sales. The market for Peanut was supposed to be children, not hobbyists (who were expected to shell out for the XT).
On the rear peripheral connectors.... there was a paper template with color-coding that you would mount to the rear bezel to ensure you plugged in a given cord into the proper socket. The cords themselves were color-coded at the connector after a while.
As for that "AMP" connector you showed. Using off-the-shelf connectors was a Don Estridge strategic decision to reduce cost. But IBM executives in Armonk were furious that the connectors were not embossed with "IBM". Later cords from IBM were indeed corporatized with "IBM" instead of "AMP".
Was this demonetized?
Not yet!
My first IBM PC was a "turbo" XT with a clock that was switchable between 4.77MHz and 8MHz via a little toggle switch mounted on the back. Interestingly enough, you could switch clock speeds on the fly without crashing the computer.
My Mom and Dad got me my first PC a Commodore VIC20 later on I managed to save up for an ATARI 800, which I still have both in my loft, I have fond memories growing up with these machines but unfortunately never being able to afford a ZX Spectrum, however they inspired me to finally become a Data Centre and Comms Room designer in my chosen career. I even still wear an old Casio watch from the 80's and its still the best watch I have at 48 years of age. We have come so far since then.
It did give Radio Shack an edge with their Tandy 1000 series of PC's, modeled after the PC Jr. (if only for color/sound).
"Until the cows come home" I thought I've heard them all. lol
I almost forgot about that pie!! Thanks, appropriately served!
For years this pc had the best diskette driver!
At the time I worked at a software house that had a software that the updates to the database come in diskettes!
The diskettes traveled by snailmail and more than 50% come with errors, other computers could not read them, NCR, Amstrad, Tandy(??),
but if we put the diskette in the IBM, we could read almost of the problematic diskettes!
At our high school, we started with TI99-4/A's and upgraded to Tandy 1000's and PCjr's (the middle school kids got the TI's after we wrote a geography program on them). Between the jr. and my Atari 400, that's pretty much where I cut my teeth coding. I would have loved to have had a jr. but that was waaaaay out of my family's price league. I didn't get a real PC until '91 or so that I bought with my own cash (486-DX33). Loved the jr. though. It was great fun messing with the guy in front of you with the IR keyboard. ;)
My first pc back in 1985. Taught me DOS 2.10, Basic, and played a handful of games. It served it's purpose for me at the age of 11.
During 80's the power adapters where heavy and bulky. However they didn't have any fan neither the CPU. Most desktop computers didn't have a noisy rotational hard drive and were more silent with the exception of the floppy disk drive occasional noise.
By the time I was messing with computers, most of them used UART16450 and UART16550 chips for Serial. The older chips were considered unusable for anything faster than about 2400 baud.
Don't call me Junior. Computer abomination. I always enjoy Dave
wow, can't remember the last time i seen any design that actually uses dedicated 74 logic dips.
Can't help but to love seeing these old computers. Old Style PCB's can look like pieces of art :)
Agreed. Frameable wall art.
That LED inside the 138440 on the modem is mad!
I think it's interesting that even the 5150 did not use an 8086. Rather they used the 8088 with half the bus a la DX and SX in the 386 era.
Dave, the floppy could not have been "360 single-sided". The single sided were either 160 KB if eight sectors per track or (with a tweak to DOS) you could make it 180 KB by jamming in a ninth sector. The dual-sided diskettes were 320 or 360 depending upon sectors per track.
This was my first computer! I took it apart and put it back together a lot as a young kid! Fond memories here :-)
My highschool received an entire lab of these, outfit with 2nd floppy expansion, and able to run in "pc mode" (via a switch on the back). IBM donated them to clear out their warehouses (and get a tax writeoff, I assume).
We used them for Turbo Pascal.
I had this, imported from the US, power converter to 100V made by a family friend. Had both the original "blocky" keyboard and the new replacement real keyboard. Also 128KB of extension RAM and floppy drive. Learned Basic and DOS really well with it. Copied drawing program from PC magazine that used the Joystic as a mouse.
Still outsold the Apple Lisa 5:1!
The main issue affecting the sales of the Lisa was the abysmal starting price, without the equally expensive ProFile external HD. The system was aimed at the enterprise user anyway.
That's because all 7 of the people in the world who could afford a Lisa had already bought one.
The MSRP of an Apple Lisa was $9995. Not exactly the same market.
WHAT A SURPRISE! Radioshack-boy had a TANDY.
18:20 This was my first computer and I remember it had a double sided, double density (720KB) floppy but not the double sided, high density (1.2MB) floppy.
Consider too Compaq started in 1982. So it was to IBM's disadvantage. And the Novation modem - I recall for Apple II's there was the Novation CAT and the program Cat-Fer.
hey... maybe put a big bright mouse pointer over the pcb screen capture. as it was difficult to see it
The trick with the jr was to use 512k external expansion and fill up the 1st 128KB to get programs in non shared memory.
Growing up, my next-door neighbor had one of these when I was in elementary school. We spent a TON of time playing Kings Quest on it. His dad worked for IBM. I think they gave it to him for free. :P
My very first computer. Once they were discontinued, they were cleared out relatively inexpensively, and made a pretty decent value for the time. IIRC, I got it with disk drive, DOS, a memory expansion sidecar and another sidecar to connect a Microsoft Mouse, for about $700, earned at my summer job between high school and college.
my first computer was a surplus IBM pcjr, with 2 floppies, 512k of memory and I upgraded the processor to NEC V20. It play games pretty good, but for the most part was a very aggravating computer to use. Every program I ran on it needed a different version of DOS. It shared video memory with the system memory.
I met a guy who had one that had so many add ons that his was 3 feet tall and had 1 foot of side cards.
The smaller Motorola chip by the IR module I'm pretty sure is the character ROM; at least one place sold a "thin line" font ROM for the Jr back in the early 1990s. Also, the other mysterious chip with the IBM P/N and the seemingly anonymous markings is the video gate array (which essentially mashed most of a CGA, the extended color modes, and I think the RAM refresh logic into one chip).
The IBM PC Jr. was NOT a failure - its presence did EXACTLY what IBM intended it to do.
Because of it, literally dozens of existing and potential businesses were either put out of business or stopped from entering the market place.
SOL, Exidy, Cromemco, etc, all bit the dust because of IBM's carefully laid plan.
Six months after the last company died, IBM dropped the PC Jr.
Many of these machines were already better and faster than the full sized IBM PC of the time.
After killing its competition, they were free to continue selling us their overpriced, under-performing junk, and it's easy to argue that it took technology 15 years to make up the difference.
I spoke to a once highly place sales person within IBM, and he as much as admitted it - they did not make unintentional moves like this.
Howard I think you're spot on about that. I remember the early days and the JR was perfectly timed to grab market share with the purpose of destroying the little guys - some of whom had great products but really really short margins and little capital.
The high price full sized IBM PC still had loads of cheaper and better competition, and the only selling argument for the IBM PC was compatibility which never was 100% for the Olivettis, HPs, Compaqs, Wangs etc. I bought my first PC in 1984 which was an Olivetti M24 with 2 floppy drives and 640KB RAM and the faster 8086 CPU for about half the price of the IBM PC.
IT is a lot worse than you think.
Wikipedia reports 250'000 units sold. I can't believe such a small number could put anyone out of business. Cromemco built Z80-based machines, running on CP/M: MS-DOS put them out of business, not this particular machine. Don't know about "SOL" (Maybe Sord?) and Exidy (didn't they make videogames?), but lots of "small" makers actually *entered* the computer market in the '80s, with PC clones that sold much better than the original IBM PC [citation needed, I know].
360k was the double sided one !
History:
PC DOS 1.0 160k (single sided, 8 x 40 x 512)
PC DOS 1.1 320k (double sided, 8 x 40 x 512)
PC DOS 2.0 360k (double sided, 9x40 x 512)
Plus the 640k limit was the way IBM laid out the memory map (Graphics card was memory mapped starting at A000:0000
Yes, when I ordered my first IBM PC in March of 1982 it was only available with single sided floppies, but in the year it took to receive the PC, I was an IBM employee so I was not a priority, they upgraded both the RAM configuration and the floppies -- I changed my order to include the upgrades. The PS/2 with 3.5 floppies and the first available HD of 20MB was a big improvement, but by then IBM had lost control and never got it back. My Nikon D800E DSLR shoots 36MP still images that are, on average, about 44MB in size each and that's compressed at that -- I'd need more than two of the 20MB HD's to fit one image.
Didn't you use a disk notcher?
I grew up in Lexington, ky. IBM was our 2nd biggest employer (the university was our first) from 1956-1990. I lived very close to the main offices. IBM was a big deal when I was growing up. There was an IBM typewriter factory here, before computers were even a thing.
The "black hole" is for the floppy drive standoffs.
been a long time since I saw 50/60Hz calibration bars. Once had a tech call in - he could not get the speed to adjust - he was using a flashlight... if the flashlight were pulsed at 50 or 60Hz it would work... but torches aren't normally pulsed
Great video Dave.
I worked for IBM New Zealand as a PC specialist and I was sent to your neck of the woods (Rosebery NSW) to be trained on the new PCjr. Even we true blue IBMers thought that it was a pile of junk. The one good thing about it, that I remember from the training, is that you can disassemble the whole unit by using any small coin. (Apart from unscrewing the system board.)
The PCjr was never actually sold in New Zealand. I was pleased about that.
The Japanese created a 'slightly' better version called the PCJX which IBM NZ and Aussie did sell. (It was not available anywhere else other than Japan.) It did not do fantastically well.
Wasn't IBM at Cumberland Forest back then?
Nope, not quite yet. They were in Rothschild Ave in Rosebury before going bush into the forest.
Rothschild Ave had the compute centre, the warehouse, offices etc. And around the corner in Morely Ave was the technical centre where they did electronic rework and other maintenance.
Come to think of it. IBM was still there in 1987. That is when the PS/2 and OS/2 came out. I was back at Rothschild Ave for the training.
I can just smell that adapter cable.
+mrlithium69 indeed!
I loved my pcjr. I remember playing King's Quest and writing little Basic programs. Jumpman was also awesome. I think we had a program called HomeWord for word processing.
My familyhad one of these with the monitor. Optical mouse on a metal mouse pad with a grid. One of the cartridges we had added memory storage, which was needed for some of the terrible games. Also had the Basic cartridge, I think it came with it.
No DOS in ROM on the PCjr (that was the Tandy 1000HX). Cassette Basic was 32K though.
What I like about this video is that Dave wants to mock it terribly, but keep stopping to give some aspects of the hardware a fair shake. The PCjr may have flopped in the marketplace, but being IBM, some aspects of the hardware were very well designed.
My first PC was this POS and yeah the connectors was just shit, you were stuck with what you had. I got it used and it had 5 of the expanders on the side, including the 512k module, even with this it was terribly slow. I had the second keyboard and used the IR, it worked alright as long you were lined up perfectly. With normal use, I had to replace the 4AA batteries weekly. Other than cartridge Basic and Lotus 1-2-3, I never saw any other cartridges. The IBM color monitor had a really wide dot pitch, I didn’t realize just how bad this machine was until I got an 8086 a couple of years later.
Regarding the way ther computer reset when plugging in the cartdrige, if I remember correctly, take a look at the traces on the cartdige PCB that made the connector part. At the moment of insertion, two traces at one end were shorted and that made the computer reset. When the cartdrige was fully inserted the traces wouldnt short, making the computer start up again. Very clever. I used my PCjr for ages. It tought me a lot about hardware and software.
Funny to see that commercial. All those floppys, and they would hold less data than microSD in my phone.
It's like IBM was trying to out Apple Apple, before Apple even knew how to Apple.
We went from something this complex to something that runs on a single chip.
Crazy to see such a lack of caps near ICs.
Marietta, GA? I used to go to school near there. Small world! Maybe I'll run into Don Bishop one day
9:05 That sponge would not fare well? But it did! It is already more than 30 years old!
That is the FIRST EVER computer I had to put my hands on... 16 colors monitor, wireless keybaord, 360k 5-1/4 drive, 128kb of memory... that cost well over 2000CAD back then... my first experiances with DOS and Basic...
HC seems to be becoming rare, even for single gate chips. Now AHC, LVC, AUC (and AUP?)
I don't get it why big PSUs and everything gave you a laugh, because they were built to last. And this is still working. Compare it to some crappy Apple hardware for top dollar they make nowadays.
Also, I can totally understand why there are custom connectors and stuff, because they used so much hi quality and expensive components, so they hoped to use it as a solid platform and make profit from selling extra peripherals and other expansion stuff.
It could be a good idea to actually compare Tandy 1000 and IBM PC jr in next video, to see if Tandy and IBM have used some tricks to reduce production costs.
Black hole.. Of course they need something to map /dev/null to!
Its failures as products like these that were the stepping stones that pushed computer companies to up the game, and get innovative instead of trying to skate the basics. Too bad companies are ran by people that forget everything they know after 30 days.
The Tandy 1000 video was *not* a clone or compatible with PCjr video. They both had an implementation of EGA's low resolution 16 color mode. There's a simple modification for the PCjr that adds the Tandy style access to that mode. If the Tandy's were "PCjr compatible" then no hardware mods would be required to run Tandy software on a PCjr with that video mode. It was possible for a properly written game to use the same graphics on PCjr, Tandy, and EGA without needing to modify any hardware. PC Enterprises sold a kit to do the Tandy video mod to a PCjr. I bought one then for the other three I modded I scavenged the required chip off things like dead XT motherboards or MFM controllers. IBM Canada had the instructions for this mod on their website in the late 90's.
Why would Tandy not make their computer *really compatible* with the PCjr? To keep people from buying software from Radio Shack stores without having to buy a Tandy PC clone to run it on to access the fancy video and sound capabilities. If the Tandy's had been out of the box compatible with PCjr, they may have sold more software but also may have sold fewer computers - to customers who already owned a PCjr. Calling a Tandy 1000 "PCjr Compatible" is like calling a Mustang II a "reskinned Pinto". Neither statement is in any way true. The computers share the same CPU, and can put the same graphics on the monitor, but the hardware is very different. Likewise a Pinto and a Mustang II could both be bought with the same 2.3L engine, but the only body parts they have in common are the rear floorpan (the rear seats are the same between the two models) and the front suspension crossmember.
The original IBM CGA has a low resolution 160x100 16 color mode that nobody used - until IBM paid Sierra Online to write a game specifically for that mode for the PCjr. Thus was born "King's Quest".
PC Enterprises also sold a kit to give the PCjr Tandy 1000 compatible sound, detectable by games that could poke around to see if the user selected configuration matched the hardware. Most games allowed independent selection of sound and video, so with just the video mod one could have beeper sound along with fancy video. But a few games insisted they had to have Tandy sound if Tandy video was chosen, and they would refuse to run on a PCjr with only the video mod - forcing the player to select 4 color CGA.
The PCjr uses the same sound chip as the TI-99 4/A. Three square wave tone channels and one noise channel that could do white or periodic noise. The Speech sidecar used Ti's speech synthesis chip. But no software used the sound or speech on PCjr to anything like what was done with them on TI's own computer.
I never bought their Tandy sound mod kit so I've no idea what was in it. Have yet to find any info online about the modification, other than it existed in some scans of PC Enterprises catalogs in archives of PCjr info and software.
The floppy drives for PCjr were double side, double density, 360K. IIRC there were ways to make 3.5" 720K drives work. The never sold in America PCjx had dual internal 720k drives, and its case was black. Shortly after the PCjr hit the market a quick and dirty dual floppy mod was introduced, but it powered on both drive motors whenever either drive was accessed. A later update to the mod fixed that. Far as I know, nobody ever made any way to use 1.2M or 1.44M floppy drives with the PCjr. There were some hard drive addons but they were expensive.
PC Enterprises had many upgrades for the PCjr. They had Soundblaster and VGA sidecars. They had plug in cartridges with various combinations of ROM and BIOS hacks and mods. They had a realtime clock that plugged between the BIOS chip and mainboard. Their Thin Font mod installed in similar fashion, with a switch to mount somewhere. What that did was enable the alternate CGA font that was built into the PCjr but for some reason IBM made it impossible to access via the usual software method. This company, and several others, made "second story" addons which upgraded RAM to 512K or 640K along with a second 5.25" floppy drive bay. They also added the modification for the second floppy without needing to take a knife and soldering iron to the stock floppy controller. Some also added DMA for faster memory.
IBM made two power supplies for the PCjr. The long, higher power one (like in this video) and a shorter one which could support at most two sidecars, usually 128K RAM and a parallel port.
There was a 3rd party modem which was faster, 9600 baud VS the stock 2400. It had to have its own buffering to avoid losing data. That pesky no DMA thing again. On hackaday.io someone is working on a way to use the modem slot for Ethernet. With a bi-directional mod to a parallel port sidecar it's possible to use LPT to Ethernet adapters. To do that and also have a second LPT requires another hack to enable changing the LPT port address.
It's unfortunate that your PCjr is a late production, fully soldered board. Much more difficult to install under-chip upgrades like a clock or to replace the CPU with an NEC V20. With a V20 in my PCjr and 22 NICE it ran CP/M faster than the Xerox 820-II I had. The Xerox was faster with CP/M than the 12Mhz 80286 I had (with 12 megabytes of RAM on ISA cards, split between XMS and hardware EMS) running 22 NICE with Z-80 emulation.
IBM had absolutely no idea how to deal a "home" or "consumer" market. The Jr COULD have been a decent home computer, The sound and graphics were good for the era, but it seems like they made much of the hardware incompatibility purposely to make it a PITA to add them into a pre-existing PC environment, Naturally protecting the "real" PCs. I could see this strategy if there were no clones and IBM had an iOS type hardware/software gated community, But they didn't. They should have just kept the original PC design (perhaps in a cheaper case?) added the new sound and graphics and pushed that towards the consumer market and pushed the AT to business (with an XT-286 for small business).
Thanks! This was a great overview.. I was around for this vintage, but thankfully have NEVER used a PC Jr.. 2 comments - I noticed a fair amount of chips that were actually 180 degrees from each other - you mentioned how they were all running the same direction, but some were backwards from each other! Check out that memory upgrade card... the two rows of memory were in opposite orientations! Is this common? I've NEVER seen this before! And, second comment - Thanks for describing that joystick interface. I've never seen one like that, and although you say most were the same design in that vintage, the old Tandy COCO used its D2A and a comparator, with the joystick as a voltage divider, which meant reading the joystick value could be slow if you cared about full resolution because you had to do up to 6 successive readings until you figured out exactly where the stick was for each axis.. I had never seen this better design to read an analog joystick! This seems a much better design, although many more parts! Thanks for all the videos.. I have learned a LOT from you!
It wasn't that much of a flop in our household, as we used it for 10 years.
My work laptop doesn't function when windows is updating....so apparently it is a time machine to 1984? Good to know.
Hi Dave, you note about the spongy stuff in the cartridge and how long it doesn't last, well its lasted over 30years!!!!
Probably back then the only D shell connectors on the adapter cable, were AMP and were that well engineered.
Are you sure that is the way the fan blows, the dust on it looks wrong if that is the case.
He is mistaken on the fan. It drew air into the case and it exited from the front of the case. There were versions of the PCjr that had standard ISO slots very late in its short life but I believe those were only for the American market. Also, many of those connecting cables were standard equipment when sold depending on the configuration the customer bought.