PCs

Cracking open the Radio Shack TRS-80 Color Computer (CoCo)

Simple times

The Radio Shack TRS-80 Color Computer was one of the first personal computers to have wide acceptance. In this TechRepublic Cracking Open Gallery we take a look at what is inside this personal computer dinosaur.

About

Mark Kaelin is a CBS Interactive Senior Editor for TechRepublic. He is the host for the Microsoft Windows and Office blog, the Google in the Enterprise blog, the Five Apps blog and the Big Data Analytics blog.

160 comments
webservant2003
webservant2003

I bought a CoCo in 1981 and it had 4K of memory. 8K of Rom on a cartridge. I broke the seal and upgraded to 16K. Whoo Hoo! Terri

joergsattler
joergsattler

I still have one of these hanging around, still functioning. With some add on gadgets i had it running for some time running theOS9 operating system of a pair of IBM Hard drives with the then astounding capacity of 5 megabytes each. My daughter used it to do her homework on it and we connected to the outside world with a unheard of speed of 2400 baud. ahhhh the good old days It still works as i write this. it is a COCO 3 with 512meg of memory installed 2 5 megabyte harddrives and 2 double sided 5.25 inch floppy drives of 360kb capacity. aaaaah the good old days

jmhintz
jmhintz

If anyone can remember the small computer called the Sinclair that was probably on the market when the first Commodore computer came. What ever happened to this company?

previso
previso

The color model got me started programming in BASIC. DOS, FORTRAN, COBOL, followed. Just a couple of years later you could buy prefab software. I quit prog for good. Yeah, right. Today I'm back in college learning C++. The irony!

promptjock
promptjock

The author implied that Motorola was the "chip of choice" in TRS-80 machines. That's not the case! the "main" TRS-80 machines (Models 1, 2, and 3) used ZILOG Z-80 CPUs and, I presume, Intel/Zilog "interface" chips between the CPU and memory. I suspect CoCo used Motorola CPU, etc. chips to respond to the rising popularity of the Commodore PET and 64 systems AND it's possible they "borrowed" Commodore designers, etc. to help them design the CoCo. Trivia: didja know the Commodore 128 had TWO CPU chips in them? yes, it had BOTH a Motorola 6810(?) CPU AND a Zilog Z-80 CPU. Ingenious use of the clock signal and "exotic" interface chips actually allowed the 128 to run Commodore OR CP/M programs. This allowed the 128 to, at the time, be "The Best Of Both Worlds" when CP/M was the predominant "business" operating environment (BEFORE PC/MS-DOS, BTW!).

redpigg
redpigg

I doubled its memory I bought it a 16K chip. Used it, well tried anyway, to decode RTTY and FAX redpigg

Al_Fresco
Al_Fresco

Back when an OS was just an OS - not a brute but an enabler.

kgwhite
kgwhite

Drove all the way from Albuquerque to Los Alamos to pick up my CoCo with an extra 32K (64k Wow) of memory. Stayed up all night copying code out of magazines and saving to cassette. Moved on to my next love the Atari 800 and DE RE ATARI. It's a sordid trail that leads me to my present condition.

mike_patburgess
mike_patburgess

I had the original gray model. Was all set to put bubble memory on it...yes bubble memory but decided instead to remove the 16K chips, install 32K chips and piggy back another 32K chips on top of these.. soulder the legs..except the sense line and then remove some other components to give the 64K more power... Worked like a charm... PS I still have the unit.. my basement looks like a museum.

williamevetter
williamevetter

The large metal cage acts as a FARADAY SHEILD, prevents inductive charges from the coils from interfering with normal operation of the components inside. Note the Holes on the cage, because those trannys got a little warm, you could not allow the ole guy to get hot so you had to have ventalation, and also you have to block harmful/nusance inductance at the same time.

Zenith545
Zenith545

Doesn't seem like much tech knowledge here. Knowledge of how to use a screwdriver and Internet search engines. This statement, "For some reason the power transformer is housed in a steel cage.", from a supposedly "TECH" environment, sounds totally naive. People with basic knowledge of computer construction and electronics could probably tell you why it is there, if not only for safety reasons. This statement, "There is one key that is different on the TRS-80 keyboard. The Break key was used to stop a Basic program from running. Ah, the days of the infinite GoTo Loop.", makes the author sound as if they don't know what CTRL-C or the Pause/Break key is for on modern computers. Can I get a job earning $60,000 a year pulling apart old technology, taking many pictures and offering little insight into the technology??? BTW - I know what the empty socket is for. Sadly, sold all my CoCo stuff, including Rainbow mags, OS-9, 5 1/4 in. floppies, drives and the "can't get along without it" tape drive, to an individual back east in order to purchase my first Intel (used, '486) machine. This is how versatile the CoCo was. Had the expansion thingie where you could plug in, I think, four cartridges, had upgraded to the amazingly fast (2 Mhz) Hitachi 63B09E processor and had an after market 1 MB board. Had to create extra vent holes in the top cover to dissipate the heat or it would not cooperate in a 90 deg. F. room. Extended BASIC was the cat's meow for the CoCo back then. Best thing was, INEXPENSIVE books detailing all the BASIC ROM's were available, making it easy for the hobbyist to create either C or Assembly language programs that interfaced with and used the ROM routines. Where is the PC equivalent of RAINBOW mag today???

jason.gay
jason.gay

Wasn't the cage around the power suppy to keep the EMF away from the CRT in the television you were using as a monitor? I would love to see the inside of a Timex Sinclair 1000, the PC I had before the CoCo.

coyhb
coyhb

You should check out the HP65 or HP67 Programable calculators. They both had magnetic card readers and onboard storage for programming using RPN logic. There not sold any more of course , and collectors think there a good investment. I still have my HP-65 that I used in an engineering department prior to the PC becoming the primary tool of choice.

ibsteve2u
ibsteve2u

...only to find out that RS/Tandy had boogered up the 286 processor wiring so that it couldn't be put into protected mode. It had another chip - whose function may have been keyboard I/O (I forget - but I remember that it ticked me off that it was non-standard) they actually named "Midnight Blue". Thus began my long hatred of things "proprietary"...although I have had to work with them, I have NEVER paid for an Apple, an IBM PC with the MCA bus, or another Tandy...

dlwm
dlwm

I still have a working Atari 400 home computer in my basement. My Atari 800XL bit the dust after a few years but that 400 is built like a tank. 16K on board memory, membrane keyboard, and a cassette tape drive... Ahh the memories.

kb0pgo
kb0pgo

This really brings back memories... The CoCo 3 was my 3rd computer after the Timex and the Atari 800XL. In truth I was more fond of the Atari. The Coco was followed up by my first truly useful computers They were an Apple 2C and the Tandy 1000XL - and one of the coolest old dinosaurs of all time. The Tandy 102!!! I think a lot of these are still in use to this day. Mine finally died last year after over 20 years of abuse. Yep, them was the good old days - I wonder If I can remember to program in basic... LOL. I think this is why I recently bought a Asus EEE machine. Portable, light, 7" screen Linux laptop the uses flash memory. It kind of reminds me of the old days without being outdated.

odracyr
odracyr

I almost bought the TRS-80 CoCo. Spent the money on a car instead. Glad I waited becaue IBM rolled out the PC and changed the world. I couldn't afford the IBM PC but later on the PCjr came out and I got that. My mass storage devices were the 360K diskette and a cassette recorder. Remember storing programs on cassette? LOL Anyway, learned BASIC on that computer and got pretty good at it getting past the machine's limitations. Good memories! :)

ajv
ajv

I still have my Sinclair ZX Spectrum and an Acorn Electron (a cut down version of the BBC Micro) both in working order and with software.

jos
jos

It was not a computer: It was an emotion. See all these comments...

jeff
jeff

As the publisher of the long-defunct "Hot CoCo" magazine, I enjoyed seeing the guts of the machine again after so long. We had a lot of fun producing the magazine! We also briefly published "Jr." magazine, devoted to the IBM PC Jr. Our main magazine for several years was "80 Micro," which was all about the TRS-80 Models I and III. Jeff

rcottrell88
rcottrell88

The ribbon cable is soldered for their repair department, I was a Radio Smuck manager from 77 at 8 mile road and Dequiner, and yes the same area as the movie, a white 20 year old who got the job for 2 reasons. I was sent there to run the store as a temporary manager, I was 20 years old, but had been the #1 salesman in Detroit for 8 out of 12 months. The manager of the store had died, standing in a wet shower, blow drying his hair with a blow drier with an old frayed cord~! Needless to say he was late for work, or is that just plain late. Too late for me, and I always said there is no way, with the items they sold, that someone could work their way into being a manager without knowing that was suicide, and it probably was. I sold 3 times what they normally did in a month, once I fired the racist pig that was the salesman and turned every black person away. I hired all people from the neighborhood and they were all black, I'm white if it matters, it didn't to me, I wanted the neighborhood to know, Radio Shack was there for them again and would stay that way. It eventually got me in the 3rd highest store in Detroit at a little over 21. I was there when people paid $699 dollars for a 4k mono computer actually it had 3583 bytes left, so it knew it was a computer. You then waited from 4 to 6 weeks, before you were called to come in and pick up your "computer" it had a basic (2 years after the stone age) keyboard and anything you saved, to a portable cassette and maybe 10 times, you could return the info to the machine, before you had to find the magic settings for each program, and saved info. Volume, tone each at the perfect place, and the machine de-magnitized every 12 hours of use, kept sealed in the case, away from speakers and you couldn't face it towards the magnetic poles because it wouldn't reload. Such a fun computer, and basic programming so magical. If X > or = 12 then goto line 26, Ect. etc. Then the big computer was born the 16k, $999 otherwise exactly as the first, until they started coming with a 5 1/4 floppy, expensive and only a slight improvement over cassette. Then Radio Shack got the bighead, built a ton of computer only stores, stealing he business from local stores, and firing Manager that went 3 months in a recession, without beating the year before sales record, without any credit given for business lost, and the year before you tripled the year before that. Eventually you hit your maximum sales and customers if you weren't in a nice area, or mall. My store was a 2 shotgun 1 machette neighborhood store, with no sign on the side of a True Value that half the people said "I never knew you were here) and Radio Smuck building a mall store a mile and a half away from me, stealing my Devry students, that the professor that expected us to have a kit in stock for all his new students, a 1000 bucks our cost and they went to the new store. Kind of like the Starbucks across from other Starbucks. Eventually Radio Shack's desire to stay with proprietory software, so when IBM and Microsoft were born Radio Smuck took a big hit, eventually closing every computer store, and eventually to now where they sell somebody else's computer. ooOOO! That had to hurt. Course we've seen 8 years of Texas "leadership". What works in redneck land, is in no way, the mindset of this Country or it's people. Hopefully soon we change history, and regain our legacy as a world freedom fighter, and not someone who bankrupts us and gives it to companies that never do their job, no bids, and computer voting machines with no backup. Come on as computer people, the question is not if your hard drive, or Windows, boot sector, overlay whatever goes south for the winter, in July. Only a fool or a cheat designs a system with no way of checking it's validity. Then a program was found on several memory cards, that all the votes were tallied on. Making both elections very questionable at best. I hear in 2000 there was a County that had -16,000 votes for Gore! -16,000. They were up all night making the mandatory count come within the margin, so no real recount was ever done. They handpicked the Counties, and results. As people who know what computers can do, we all should be very mad, and watch them like a hawk, or Microsoft and all their money and lawyers. The only way in today's economy, and environment to feel safe, and have a voice. This post wouldn't fit on the first $700 4k mono system. The color computer for the first year plus had 64k, and later a few 128's. It's like kinescope, compared to HD, somebodie's coming out with Don King hair, looking like they were hit from Larry Holmes or George Foreman, with his biggest grill. That man has some serious need for me to be his best friend. Haha! Hey, my Grandpa was named George, and there was talk about the black hired hand and Great Grandma, or she was at least very good Grandma, haha! Grandpa George, it's me your long lost white grandchild. he'd probably say not lost long enough, and besides they didn't name me George, and he don't tolerate that. Would you say something to him? I like my jaw, still attached, that's the way I remember it coming. What are the best use of your old Co-co's? 1. set them up in the visitor room you setup when you want the company to leave the next morning, hopefully before you wake up! 2. Your cat's computer, a moving picture on the screen and some place warm to sit. 3. By the front door, as a security device, you pick it up and smack the intruder with it. 4. A guilty turn in for Goodwill for the write off and 20% off coupon. 5. sent it to George, so he can be like the other big boys and have his own computer. (it was never hooked up to anything else) so no news to read. Woudln't want to ruin one of his 4 vacations a year. 6. Send it to Linda Tripp and tell her to put it in front of the camera if she sees a camera. A Man can only take so much of her.

themurray512
themurray512

I still have my first TWO computers: MC-10 Micro Color Computer and CoCo 3 with 512MB of ram, plus a boat load of hardware add-ons! I used it access internet via UNIX to read email and other unix commands!

ltoribio0
ltoribio0

When I first heard about the CoCo back in the early 80's, I shrugged it off, thinking it was a toy. I already had a TRS-80 (pronounced "trash 80"). But I ended up buying one, which I upgraded to the max (beyond even what Tandy could do). I ran OS-9 on it and used it as a timesharing server for two other CoCo's which I eventually bought. I also used it to produce videotapes for presentations that I gave on various IT topics. It turned out to be surprisingly versatile. Leo Toribio

thansen
thansen

MY 1st computer and what taught me the foundation I needed to start my career was the IBM PCjr. I feel the PCjr has earned a place in history with it's 'sidecar' attachments and upgrades. Would love to see one split open again.

luisp
luisp

Hey! I remember those! LOL! The nickname was "Trash-80". This was the time when Bill Gates had states, "640K ought to be enough for anybody." I wonder who was his adviser at that time... Thanks for the tear down. Always nice to see the art of engineering from the inside out. Luis

bintekster
bintekster

I believe Caged Monkey is correct. The ribbon should be able to be pulled form the black socket that is holding it. The mechanisms used today have a type of latch that can clamp "together" a ribbon cable in a socket. But before these systems existed, Ribbon cable sockets were made to just have a tight fit. The trick to taking one of those ribbons in and out is grasping the ribbon near the top of the socket between your thumb and first finger which is normally in a curled position. Rock the ribbon gently end to end while pulling up. You'll feel the ribbon giving slowly at first but then it should come out. Care to putting the ribbon back in is using the same principles. This will keep you from ripping the ribbon during removal or bending it when replacing it. I used to work on the US Navy's C.I.W.S. Phalanx system ( Block 0 ) which definitely was around before the TRS-80 and at various points had cables like this. Hope this information helps.

Oreamnos_americanus
Oreamnos_americanus

I remember opening up the case to max the memory. Then buying from some surplus place a incredibly heavy (45lbs !!!) case containing two Double Sided, full height 5.25 drives manufactured by Digital Equipment Corp (DEC), god only knows for what! Then adding a CoCo tape disk controller cartrige to give me 4 drives as each side of the floppy was treared as a separate drive. Never got around to installing OS-9 as I sold the whole thing to another CoCo nut & bought an XT clone PC-20 built by Commodore with an add on EGA card, 720K 3.5" drive, and external 1200 baud modem which came with it's own permanently attached phone. It quickly gave way to a 2400 baud internal and it was off to local BBS services and a Compuserve account.

CagedMonkey
CagedMonkey

The yellowish tint on the transformer is varnish. When the transformer is made it's dipped in varnish to keep all the layers of the core together.

docflash
docflash

There was an operating system for the old CoCo called Os9, which was a unix based system that when properly configured actually ran multi user/ multi tasking. Talk about too much time on your hands, when I worked for a Radio Shack computer center we took a full blown 128k unit and two 32k units 4 CoCo floppy drives and actually had a working 3 user demo. Extremely slow by today's standards kinda like Fred Flintstone in comparison but actually worked!

mike
mike

Did anyone else own an Amstrad CPC464? My parents chose this over a C64 for me when I was 7. I remember being devastated due to the lack of games and that some of my friends were getting C64's. I'd like to see you get hold of one of these and crack it open.

abuttery
abuttery

I hope you realize that the keyboard on the one you cracked open is an upgrade to the original "chicklet" keyboard the machines first came to market with.

lylejk
lylejk

My very first computer (believe 1981). Later, my dad got me a CoCo 3. These were quite enternaining for me. The 6808/09 processors were like having your cake and eating it too. But Intel became the King. :)

dcook
dcook

We had a couple of CoCo/OS9 Users groups up here in the Twin Cities. I ran the OS9 BBS for about 2 years out of a walk in closet in our tiny apartment before we bought a house in about '86. OS9 - WAY before its' time. Small kernel, PIC, Ext Indirect Addressing - back when MSDOS could only do PIC w/12 CPU cycles - OS9 in 1 or 2! We built a SCSI HDD interface using a PIA chip. Slow, but allowed HDD. I still have 3 or 4 units in boxes but I think my wife threw out the SW.

jlapp
jlapp

I still have mine. Any offers? I also have a late 60?s vintage cassette recorder that can load the games and record your basic programs. This is an awesome walk down memory lane. My first computer was a Timex Sinclair but I sold that to buy my coco. It was expandable to 32K of ram which I did. What a power house!! And yes, the transformer cage was to protect the video from 60Hz EMI. This was analog video into TV with a 60 Hz refresh rate. Just out of curiosity I would love to know how old the kid was that wrote the article, but regardless, well done and quite entertaining. I have cartridge games too, checkers and a few others. My favorite was a tape game called bedlam. Now I have to dig it out and see if it works! My daughter will be impressed I am sure. ;o)

s.perry
s.perry

ahh low power schottky TTL those were the days! hand warmers to boot!

CagedMonkey
CagedMonkey

I remember that little bugger with the membrane keyboard. Powerful little bugger for the size. There used to be rather large user group for it here in Portland, OR

CagedMonkey
CagedMonkey

A buddy of mine up in Alaska has been using a CoCo3 for ages to run a custom designed 3-D wood carving business. He originally was using it to only carve wooden signs and eventually turned it into carving metal electric guitars. He's been doing some pretty cool stuff on that old box.

Mark W. Kaelin
Mark W. Kaelin moderator

I like to earn that too. I have an idea why the power supply is in a cage, the point is that the power supply is in a cage instead of some other enclosure. Please understand, I am not an Electrical Engineer. If you would to share your knowledge with the rest of us, I will gladly pay you to do so.

Tech Locksmith
Tech Locksmith

While I no longer work here, I do feel that someone should point out that if you don?t know where you?ve been, it is difficult to know where you are going. I slightly distrust programmers who only use object oriented languages without experience writing machine language. OO is GREAT, but you still need to know the basics and CoCo taught a LOT of us the basics of hacking. As for where Rainbow is today, it is right here as well as other places online. We did cutting edge things in Rainbow such as publishing programs on vinyl.

dimple
dimple

What an honor to see your posting! Good to meet you I am Steven, I used to subscribe and read Hot CoCo all the time, in fact I remember getting that last issue was very sad to see the last pages notice. Roughly saying it is being integrated back into the magazine that gave birth to it. I knew it would not be long after that. I am from Ohio too! I oddly enough moved to Albuquerque with my CoCo2 for college, this was about 3 years after Bill Gates moved his operations from there to Redmond. We of course know MS wrote the CoCo Basic ROM code. CoCo 3 was a nice machine, they should tear one of those down here too. I have 3 CoCo 3's, 3 MultiPaks, disk units, Cloud 9's Flash/HD controller with Drivewire brings CoCo pretty close to the 21st century, lol. Check out my site www.cocolives.com still under construction. Long Live CoCo!!!!

Tech Locksmith
Tech Locksmith

I wrote for Lonnie for years at Rainbow and PCM, still have a few copies of Hot CoCo around along with a stack of Rainbow and four or five CoCo's. Later did the CoCo column for Computer Monthly. Remember running multi-users using OS-9? John McCormick, siliconsamurai

wordmaster1
wordmaster1

I know what you mean. I went even further. I opened it up, soldered in a full 1 meg of RAM, managed to get two double sided 3.5 floppy drives working and even put a SCSI hard drive in that puppy. I did install OS-9 and have run as many as 12 keyboards and monitors, all doing different things at the same time on that "old" "antiquated" computer. The one thing I never did that it was famous for being able to handle was to use it as a total environmental controller for my home.

CagedMonkey
CagedMonkey

That keyboard is not soldered in. It's a flex cable and can easily be removed from the connector. The connector is soldered to the motherboard but the flex cable is not.

Vorpaladin
Vorpaladin

We had a good size user group here in Charleston SC too back in the day. I have 3 of these things; two are branded as Timex-Sinclair, the other as ZX-80. I built a voice synthesizer back in 1983 and interfaced it to one of my ZX machines and wrote machine code to control it, which was a challenge with the 4K limitation, especially since the 4K of RAM was shared with the display! That was a fun project. I loved playing around with those little machines. The ZX, along with the CoCo changed my life. After writing a handful of games and simulations for the CoCo, I was hooked. I'm 42 now and have been a professional software developer for over 20 years, due primarily to the influence of the CoCo and ZX.

172pilot
172pilot

You say "slightly" distrust programmers who only program in OO languages.. What an understatement!! You'll get a kick out of this one.. A friend of mine, who I met BECAUSE of our common love of the CoCo was working at a big development shop which shall remain nameless to protect the idiotic... One of his "top" programmers had to figure out a way to read a single bit out of the middle of a bit-mapped return code... You know - the kind of thing an old coco asm. programmer could do in a couple of clock cycles.. Well, this guy ended up with a 128 level deep if-then-else sequences to query whether the byte was any one of the possible combinations that would indicate that the desired bit was set or not... Hand-typed, and manually calculating each byte value along the way.. Understanding that this is the state of our "college minted" application developers, it is not hard to explain why something like Vista needs a 2ghz processor just to provide the horsepower to run the O/S effectively... That programmer, although in my opinion, he should have been fired, was simply embarrassed to death when he was shown how his pages of if/thens could be replaced by ONE line of code and a little binary and'ing..

CagedMonkey
CagedMonkey

I still have many of my old books from back in the CoCo days and like to look at them. I just wished I had not gotten rid of all my Rainbow magazines! You never know when some trivial little piece of code might solve a simple problem. Gotta remember KISS! Everyone wants to make things more convoluted than neccessary. I still to this day always try to optimize my code. I'm always looking for an easier way to do a task. Heck that's what got me hooked on programming in the first place.

os9dude
os9dude

Funny and *sad* story up there. I got the visit at my office of two college level students on their 6th semester (school name withheld to protect it's geek factor) sent my way via someone that knew me from my CoCo hacking days. These two young guys - Computer Systems major - had been left with a project that within required to evaluate PRIME numbers from ODD ones on a list, therein lies their problem: they were up to snuff on OO languages, but couldn't find a 'library' or canned-code to get them across that small hurdle, they had a convoluted process to resolve it and their teacher asked them to simplify matters a bit. Intentionally, feeling they wanted a quick way out of it, I wrote up while explaining the SIMPLE MATH BEHIND one solution as a Basic program straight from my CoCo days. The 'logic' escaped them somehow and reluctantly took the piece of paper with the 4 or 5 lines of Basic code. I was dismayed to see this. Granted not all students are on that spot but it shows what's out there on "the job market".

CagedMonkey
CagedMonkey

Too many people (Microsoft included) write sloppy code and don't remember the old KISS theory. Sometimes the hardest problems are solved by the old tried and true methods. Don't always need fancy OO to solve simple boolean logic. Just like for me. About a week ago I was frustrated beyond belief trying to solve a ColdFusion programming issue using Flash forms with multiple related select lists that defaulted to specific items. I searched forums all over the place trying to figure out my problem for about 3 days. Then it dawned on me that I could solve the problem using what was already at hand the basic list and it's built-in properties of using the 'selected' option. DOH! Sometimes the answer is right in front of us and we have to remember the BASICS.