Ah, my Atari days *swoon*. Learning 6502 assembly on an Atari when I was 14 made me the person I am today. ahahahahah
Atari 8-bit and Commodore machines (and Apple II as well) did share a common 6502 CPU, but the coprocessing chips for graphics and sound are really what separated these machines. Apple's capabilities were far inferior, but it also was released years before the others. (If I remember correctly it was 1977, 1979, and 1982 for the Apple II, Atari 8-bit, and C64).
Atari developed three specialized chips for these computers; two for graphics and one for sound, building on what they learned from the original VCS/2600 machine. Programming these machines is primarily a matter of mastering these three chips.
Unlike the 2600 game machine, there was indeed a frame buffer on the 8-bits, and Atari engineers did some really neat tricks to make interesting use of display memory, allowing programmers to display things differently in horizonal strips down the screen, trading off memory usage, pixel size, number of colors, and text display. As a kid playing lots of Atari games back then, you quickly noticed patterns in how the screen was always laid out -- scores and status along the top or bottom, fancy graphics in the middle.
Commodore's entry a couple years later was suspiciously similar in capabilities, but in a massively cost-reduced form. A big leap in sound tech, but a step sideways or backwards in graphics. In junior high we sat at different lunch tables, emotions ran pretty hot on our nerdy brains back then.
Jack Tramiel never gave us a shiny, white telephone or mp3 player but he was very much the same conniving, non-technical pitch-man that Jobs was, less the presentation polish and boyish good looks. If you look at Commodore during and after his reign there is a marked difference. They're also both very interesting people who should be respected for what the accomplished and often vilified for how the accomplished it. Neither should be your role model IMO.
In some ways though Jobs and Tramiel are polar opposites:
Tramiel was interested "in computers for the masses, not the classes" so it was all about "rock bottom pricing" and undercutting competitors; Jobs especially in his later days was interested in premium products and eventually luxury products.
Tramiel never understood or invested in growing a platform or growing, expanding, intercompatible product line. Each Commodore machine under his watch was a brand new machine, not compatible with the others except for maybe a few peripherals.
At Atari Corp they did seem to learn a bit more on this front, with a series of models all compatible with each other... but innovation and development on the operating system basically stalled from 1985 until about 1990. TOS 1.04 was really only small incremental improvements and bug fixes over the original (quite fantastic for its time) release and it came out in 1989, 4 years after the initial launch.
And I get the impression that the early 90s push at Atari towards multitasking and major improvements in the OS might have come at the behest of his sons taking over and their attempt to try to get into the workstation and DTP market.
By 1991/92 it was too late. The Atari Falcon was an awesome computer, and the final versions of TOS/MultiTOS were respectable for their time, about equivalent on paper with Apple's MultiFinder and with Windows 3.11. But there wasn't a community of devs or a broad enough audience for the product, and Motorola had marked the 68k line for death.
> Tramiel never understood or invested in growing a platform or growing, expanding, intercompatible product line. Each Commodore machine under his watch was a brand new machine, not compatible with the others except for maybe a few peripherals.
But, iirc, very very very few computer manufacturers prioritized compatibility in that way in those days though, and for good reason, it would have be stupid expensive. Some manufacturers got around the problem (Commodore did this as a matter of fact) by incorporating all or part of the previous line in the new machines and enabling compatibility modes.
> But, iirc, very very very few computer manufacturers prioritized compatibility in that way in those days though, and for good reason, it would have be stupid expensive.
You don't recall correctly. The only major brand that didn't prioritize compatibility was Commodore.
Maintaining compatibility limited the ability to add new features but it wasn't 'stupid expensive'. What is expensive is throwing out what you have and creating something incompatible from scratch. When you have hundreds of thousands or millions of units out there, not being backward compatible means you risk losing most of those customers.
Nearly everything that ran on the original Apple II ran on the IIe and IIgs, and nearly everything that ran on the Atari 800 ran on the XL and XE models. Nearly everything that ran on the original 1981 IBM PC can run on a modern PC compatible.
c128 was a case of idle engineers with no plan/strategy gluing unsold garbage components (graphic chip left over from earlier failed project and Z80) to c64 and scamming public with misleading name. 2 CPUs, 2 graphic chips, 2 monitor outputs, all in one package.
Even without a C64 mode, the C128 is a cool system. Dual monitor outputs, 128K RAM, 2 MHz 6502, great BASIC, fast floppy drives. The only thing that would have been better would have been to add these things to the C64. Also nice: dual SIDs.
They could have added all of the above without breaking backward compatibility. This would have encouraged programmers to check for the enhanced features and use them if available.
Of course, long term, they would have needed to go with the 65816 and ultimately switch to another processor architecture.
I think if all of the 8-bit and 16-bit systems had survived until today, they would all be running on Wintel hardware but with their own operating systems, just like Apple Macs.
Well, that's simply not true for the Atari 8-bit line (mostly compatible from 1979 right through to the XE series which continued right into the late 80s and even early 90s), the Apple II line (II, II+, IIe, IIc, IIgs, as well as cards that slotted into Macs), MSX and MSXII, and of course the 16-bit era with MS-DOS machines and Macintosh, Amiga and Atari ST lines.
Honestly, Commodore and Sinclair 8-bits are the outliers here? C-128 came quite late in the game.
Commodore did have a fair bit of compatibility within the PET/CBM line.
The C128 is a good example of how Commodore did compatibility wrong. Instead of creating a 100% C64 compatible mode, separate from the C128 mode, they should have taken the C64 and added a second bank of 64K of RAM, an MMU, an enhanced VIC-III with added registers for the enhanced graphics (eg. colors, resolutions, sprites), a second SID, a 2 MHz CPU, an enhanced KERNAL, and an enhanced BASIC that had the same tokens as BASIC v2. While C128 mode was very similar to the C64 mode, it wasn't enough to run hardly any C64 apps and games without modifications.
I don't blame Bil Herd for what the C128 is though. It is a great computer, especially considering he was fighting the top levels of Commodore to get it out the door. If he'd had more support, it could have been better.
I feel like the right way to do it would have been to have shipped a C64 compatibility mode in the Amiga, instead. An A500+ with a 100% C64 compatible mode capable of running a C64 in a window even, IMHO would have been great product that could have sold like gangbusters because the C64 was still a hot selling product right through the late 80s. I can't imagine it would have been that expensive to do given how well understood the C64 architecture was at that point.
Either that or have built the Amiga around a 65816 or similar instead of 68000. Like the IIgs but with even better sound and graphics.
> Either that or have built the Amiga around a 65816 or similar instead of 68000.
This would be a huge mistake. The 68000 was much more elegant and had a way forward, something the 65816 never had. Had they gone the 65816 route, there would never be an Amiga with a better CPU except, maybe, a faster one.
And the whole Amiga 1000/2000/500/600 was saddled with TV signal timing dependencies that made it more difficult to have better graphics and ended up having to play catch-up with VGA and Sound Blaster.
65816 at 7MHz would be faster than 68000 despite 8 bit databus. one modified for full 16bit would fly circles around motorola. Bill Mensch would have no problem extending and growing this chip as long as Commodore was buying. 65816 already has reserved mnemonic for expanding instruction set further.
The 65816 (much like the 6502 before it) punched way above its weight, but that'd not be enough in the long term.
There was a point neither IBM nor Motorola cared about making PPC CPUs for Apple - that's why Apple moved to Intel. Moving to a bespoke, Apple-only CPU, would only precipitate things by making a series of CPUs just for Apple. Not sure WDC would be able to rival the investment of the big CPU shops of the time.
If, instead of tapping WDC they went to MOS with a roadmap that could accommodate both Apple and Commodore, maybe history would be different. In either case, these are parallel universes I'd love to observe.
This chip wasn't ready when they were building the C128. It was later included in the C65.
But, apart from that, there is a lot Commodore could have done incrementally with the C64, making it iteratively more functional without breaking backwards compatibility that the company simply didn't want to.
> he was fighting the top levels of Commodore
The 128 shares a lot of sins with the Apple /// and comes from a very similar story. At least Apple learned something from the /// and made the //e, //c, //c+, and the IIgs (lovely, albeit kludgy, machine, which was an absolutely idiotic project that only took resources away from the Mac). Computer for computer, an LC with Apple //e PDS board was a smarter choice.
IIgs was a lovely machine that was kludged and handicapped because they didn't want to take resources away from the Mac. They could easily have clocked it up 4mhz or higher and had a much more capable machine. But my understanding is they didn't want to eat into Macintosh market share.
But schools here in Canada at least were highly invested in the Apple II, and my school acquired a whole fleet of IIgs machines. They were pretty nice actually. If they'd clocked it higher it would have been a very worth competitor for Amiga and Atari ST. But they didn't.
> handicapped because they didn't want to take resources away from the Mac.
They had resources. The IIgs had a ROM Toolbox, a lot of hardware and was, overall, a very complicated machine that took multiple iterations to be developed. Apple was trying to make a 16-bit Apple II since before the Mac.
That they didn't want it to take sales from the Mac, makes sense. The IIgs was an evolutionary dead-end. There was no successor for the 65816.
No matter what they did with the 65816, it'd still have segmented memory, few registers (somewhat aleviated by the single-byte address trick) and no way forward - no MMU, no FPU. WDC still makes them, and never made a 65832 or 65864. The ST and Amiga were excellent opportunities thrown away. Commodore could have the 3000 be the entry-level Unix workstation Sun would sell and, with that, gain a foothold of the technical and financial desktop market. Commodore had the professional video market thanks to the Video Toaster, but made machines where the Toaster wouldn't fit. Atari, OTOH, made a couple decent workstations, but never invested much in anything beyond gaming machines with tiny monitors. It found a niche in the Music segment thanks to its MIDI interfaces, the same way the Mac survived because if was at the right place to take hold in low-end publishing.
I rode the Atari ST wave back then. Until I bailed and got a 486 and ran Linux in 93. Yes, Atari half-heartedly marketed the TT030 as a Unix workstation, but it never stuck. I still remember the headline of the little snippet in UnixWorld magazine about it "Up from toyland." Not taken seriously in the Unix market, really, and by the time they had a product, that wave (68k based Unix workstations) had crested anyways.
The real problem for both Commodore and Atari in that era (apart from moribund sales, small market, bad management, etc) was that Motorola was already working towards killing off the 68000 by the early 90s. I'm not sure what Atari or Commodore would have done if they could have held on another couple years. PowerPC ended up being a dead-end, too.
Yeah, I don't like programming the 816, either. But in that era it wasn't the worst. WDC made the 816 just for Apple, really. (And didn't do the greatest job imho, but whatever) If Apple had asked for it, they would have made an 832, added more registers, whatever. It would have been a hack... but so was x86.
Apple's problem was that until the LC (93? 94? 95? I forget. My mom bought one at my recommendation) they didn't have a reasonably priced low-end Mac to sell to people or schools who would have gotten something in the Apple II series in the past. They seemed to have lost a big part of the education market when they dropped/failed-to-advance the II line.
> reasonably priced low-end Mac to sell to people or schools who would have gotten something in the Apple II series in the past.
Even with the heavy discounts Apple gave to the education market (brilliant strategy, BTW) the Apple IIs were not exactly competitively priced. So much, in fact, PC clones ate away the educational market with a product with a much higher perceived value (kids would learn to use the computers that were going into offices).
As a Canadian I am surprised to hear schools, "were highly invested in the Apple II". In Ontario and any other province I've heard about, Commodore PET, VIC-20 and 64 were nearly ubiquitous. What province were you living in?
Even if clocked higher, the IIgs didn't have the video power to compete with the Amiga. No blitter, sprites, or hardware scrolling.
What Apple product wasn't priced too high? Always have been, since day one.
ok, I stand corrected, but I will say that the Apple II line represented smaller iterations of the generally same architecture, right?
i.e., Commodore I guess didn't iterate within the same architecture as much, breaking that compatibility more easily.
One of the key difficulties of making a faster Apple II was the time-critical routines involved in reading/writing floppies. It was not sufficient to throttle back to 1 MHz when running time-critical loops, but one would need to emulate the timing of a 6502 doing that. Commodore made a better 6502 for the C65, but it'd wouldn't work on an Apple II because it wouldn't have the same cycle timings.
The IIgs and the //c+ was faster and very compatible thanks to a crazy number of hacks in them to acommodate Woz's brilliance.
In retrospect, Apple should have released a Disk II+ that isolated the timings from the CPU and let software break. Commodore should probably have done the same.
I have to laugh when people call the C128 a market failure. It sold 4.5 million units. The C64 sold 13 to 27 million units (depending on who you ask). The Apple II line sold 5.5 million units. The Sinclair ZX Spectrum sold 5 million. The MSX line sold 5 million. The Atari 8-bit line sold 3.5 million. The Tandy Color Computer line sold 3 million. The Amiga line sold 11 million (6 million were the Amiga 500 model). The Atari ST line sold 5 million.
The C128 only looks like a failure when compared to the C64 which it was compared to a lot for obvious reasons. Compared to the rest of the industry, it was a smash hit, even if most people used it in C64 mode.
If the entire Commodore 8-bit line had been backward compatible like the other manufacturer's computer lines, its total would be 20 to 36 million.
That number is very strange. It'd make it outsell the C64c over its lifetime even though both computers coexisted and Commodore killed the 128 in favor of the still more profitable 64c.
> The MSX line sold 5 million
About 9 million, according to Wikipedia, but I would bet in higher numbers because they were manufactured by a lot of different companies, marketed under lots of different brands in a lot of different countries. We know they sold 7 million in Japan alone (probably counting MSX, MSX2, 2+ and Turbo R).
I remember one of the documentaries he was openly talking about how he locked out competitors when at atari. He did it by buying up fab space in any company that could make something for a competitor.
"After the 400 and 800 launched, power users awed by Star Raiders proved eager to flex the machine’s advanced capabilities. But Atari, following its closed model with the 2600, had never intended to spill the secrets of the HCS architecture outside of special agreements with contracted developers. Crawford recalls, “There were about half a dozen people I knew who’d been bugging me for that information, and I had told them, ‘No, I can’t tell you anything.'”
Ironic that it was the Atari that seemed like the "closed system" then. I had a 400 with the horrible membrane keyboard (hey, it was cheap) but there was no documentation on how to program it outside of BASIC.
For Commodore, we had the Commodore Inner Space Anthology, put out by the wonderful people who published The Transactor magazine (http://csbruce.com/cbm/transactor/).
That book was amazing. The Atari Assembler cartridge and magazines completed the picture of what you could do with the Atari 8-bit. I know there was another book I loved, but I cannot remember its name. I have them in a storage garage along with my 400 and 130XE.
I had friends who had the Action language cartridge but I never got to play with that one. Apparently there was information there about the machines internals.
I had an 800XL myself <3. Because my parents couldn't afford the more popular commodore 64 here. The commodore had a 6510 by the way but it was almost the same.
The display list interrupt was indeed really cool, combining different strips of video modes. The one thing I did miss was combining different text colours on the same line. The commodore could do this, the Atari couldn't.
The sound wasn't as good as the SID, but it was still better than any other sound chip at the time. It had four voices when most chips had three and two of the 8-bit channels could be combined into a 16-bit channel, giving one 16-bit channel and two 8-bit channels, or two 16-bit channels, giving much better sound quality.
The Ataris had Player-Missile graphics, sort of like sprites that were specially/easily handled. I seem to recall that there was one player (16px wide x screen height) and 4 missiles(4 px wide x screen height) that could be cheaply moved back and forth across the screen. There was some collision detection between them and other things that were on the screen.
The Apples had several graphics modes, many of which were strange and somewhat pointless on a green screen (yay for some colors in even columns, some in odd), but nothing special to accelerate games IIRC. On the other hand, they had a lot more memory and they felt about a generation ahead. The 800 seemed like an advanced 2600, but the Apple felt like a real computer.
However, speaking of generations ahead -- the Atari 400 beat the 2016 MBP to the punch in the horrible flat keyboard race.
Ah yes, the player/missile graphics :) Actually there were 4 "players" 8 px wide (although you could of course put several side by side) and 4 "missiles" 2 px wide (the name already gave away that you couldn't draw much more than a bullet with 2 px of width). The width of the "sprites" could also be stretched, but you could only move them horizontally in BASIC - for vertical movement you had to actually move the sprite's bytes in memory, and BASIC was too slow to do that smoothly. I had a 800 XE (the German version of the 130 XE - the same Atari ST lookalike design, but only 64 K) and programmed some games/"demos" in BASIC which I still fondly remember. One of them was a train with a steam engine and 3 carriages (the four "players", the carriages were double-width) which rolled over the screen. Another was a game in which you could bet money on one of four snails (again the four players) - the snails would move a random (small) amount, then pause for a second, then move another random amount, until they all reached the finish line. Nerve-racking action!
IMHO real historical value of the 8-bit Atari is that it is the "father" of the Amiga (which offered a lot more bang-for-the-buck and technological advancements than the Macintoshes and IBM PCs of the time). Many of the Amiga's core ideas (like a separate display coprocessor which ran its own 'display list' programs) had been tested on the 8-bit Ataris already, by the same design team.
That's a pretty funny way to frame it "the real value of this historical artifact is in the fact that it was the father of this other historical artifact that I personally like/prefer".
You could just as easily say the Atari 2600, which Jay Miner also worked on, only has value in that respect, but you'd also be wrong.
Yeah the Amiga was pretty cool. But so were lots of other things.
Also the designer of the Atari SIO, Joe Decuir, also worked on the USB standards and calls the SIO the direct ancestor of USB. Too bad it's so slow. The Commodore VIC-20 and 64 (which had a similarly crippled serial interface) and Atari 8-bits all would have been even more interesting machines with a fast parallel floppy interface.
I still have my 800. It was given to me sometime in the 80s when my cousin passed. It came with the BASIC cart, a tape drive, and a book called something like 101 BASIC GAMES that were just copies of source code. That machine started me on an obsessive path of learning languages and programming at ~10 years old that was all-consuming until I graduated high school. I hated the stupid membrane keyboard, but the lessons learned on that machine were invaluable to my curiosity.
Pretty much same story here -- few things affected the path of my life as much as that one device did. I cannot overstate its impact on my ability to get creative with limited resources, seek out and solve tough problems, and have pride in creating things for others.
I remember really struggling to get the tape drive to work. Sans internet, it was quite a challenge to figure out how to get it going. That was quite likely the spark that made me want to learn anything and everything about hardware.
I'll have to dig it out. I don't remember the illustrations. I remember working on a blackjack program forever. Debugging line by line. Finding my typos and getting it to work. That was one of my proudest moments.
> But also in retrospect, stretching the budget to afford the computer was well worth it since it gave you and your brother valuable skills worth more than money.
I bought my Atari 800 and a disk drive using newspaper route money. Probably the best investment I ever made.
Burned my modified Atari OSs into switchable eeprom boards, built the 256k memory expansions for the XL series, and made a kit for builders at the user groups. Still have them, all original 400,800, several XLs, and hundreds of games. Moved to the Amiga where it was so very much advanced, having admin'ing the SGI (4D/440), a MicroVAX II, Suns, and helped with Evans and Sutherland workstation. Spent a lot of time in Palo Alto, Sunnyvale, Mt. View, as well as haunting out the old Atari buildings and all the prototype junk that ended up at the surplus stores..
I like hearing about Atari 8-bit computer owners who upgraded to the Amiga, both designed by Jay Miner, instead of the Atari ST, which was more of a 16-bit Commodore 64 than an Atari, being designed by one of the engineers of the C64, Shiraz Shivji.
The funny thing is both Atari and Commodore outsold Apple in the PC market. IBM really took its market share from Commodore rather than Apple, but neither Commodore nor Atari had Steve Jobs. It would have been funny if Steve Jobs had hooked up with Jay Miner for the NeXT era.
Its sad neither company did their transition to 32-bit well. Amiga and the ST were awesome, but they lost that low priced magic and availability that marked their 8-bit entries.
Did Atari outsell Apple? In which years? Ultimately, the Apple II line sold 5.5 million units while the Atari line sold 3.5 million.
What I get a kick out of is that even though the C64 came out a year later than the IBM PC, the C64 very quickly outsold the IBM PC and it took five years for the PC and clones together to catch up and surpass C64 unit sales.
Steve Jobs and Jay Miner would have been interesting. Jobs never seemed to care much about powerful graphics. Neither the Apple II nor Macintosh had graphics acceleration, so I'm not convinced Jobs would have felt any need to work with Miner. Jobs didn't seem interested in having lots of color, hardware sprites or screen scrolling which were beneficial in games.
By 1987, I was out of grade school and could afford to upgrade my C64 to an Amiga 500, so I didn't mind that they weren't marketed at the masses, even though I probably would never had gotten into computing if the VIC-20 my parents got me at 13 had been more than $300, but a number of friends who had C64s ended up going the IBM PC clone or Atari ST route to fit their budgets, or perhaps I should say, their financial priorities.
> Did Atari outsell Apple? In which years? Ultimately, the Apple II line sold 5.5 million units while the Atari line sold 3.5 million.
Atari outsold Apple worldwide from 1979 to 1983 (two years after the IBM PC). The PC outsold everyone in 1983 except Commodore. Strangely, no ones talks about the TRS-80 outselling Apple from 1977-1982.
Steve Jobs has demos for NeXT about how good the graphics were (his drag showing the windows contents). They also built the NeXT Dimension which was supposed to support video and graphics. I seem to remember there was something that prevented its full utilization.
Back when Atari was a computing giant together with Apple. Now, it is widely remembered as a retro gaming console that is catered for nostalgic crowds.
It has been a long time but I seem to recall the Atari and Commodore systems were practically clones of each other. I remember this because all the good games appeared at retailers simultaneously for both systems and I was an unfortunate(or fortunate) child of the 80s who's father was of the opinion that the Texas Instruments offering was a "Far better Machine" and that he "Wouldn't waste money on a gaming system!"...."Far better Machine" is exactly what he also said about Beta Vs. VHS too!
I must say I would thank him now if I could for not buying a "game machine" as I believe it prevented my brain from developing as many addictive synapsis at such an early age.
> but I seem to recall the Atari and Commodore systems were practically clones of each other.
That couldn’t be further from the truth. The only thing they had in common was the CPU. Apples did everything with discrete logic and graphics were a bit primitive, and color depended on NTSC artifacts. Sound was done by the CPU controlling the state of the speaker, pushing out a square wave. If you could hog the CPU, you could do PWM audio, but it wouldn't sound great.
Ataris had outstanding graphics. Their “GPU” ran a display list that generated the video output. There was no such thing as a frame buffer or a video mode - everything was rendered on the fly. Sound was OK-ish, driven by a sound chip. Ataris also ran the 6502 at twice the clock of the Apple and Commodore.
Commodores had somewhat more primitive graphics than the Ataris, but compensated that with an excellent palette and a sound chip with very sophisticated capabilities.
interesting, I wonder if the common cpu made it easier to port the games for those two systems or possibly a shared compiler?
I'm pretty sure the TI994a had somewhat of a video buffer in the form of sprites (I know it was capable of parallax scrolling) and it's own sound chip that was the one used in speak and spells(That may have been a separate module called speech synthesizer).
Later models of Atari and Amiga may be the units I am thinking of being very similar.
Outside of the instruction set of the 6502 CPU there was zero overlap between the C64, the Atari 400/800 and the Apple II. There were no common tools to speak of, no common data formats, no compilers (compiler? pshaw! sub-optimal code!), no common memory map, no common audio hardware, and between the Commodore/Apple/Atari of the time, there wasn't any commonality in how the screen memory could be read or written. The BBC Micro (also 6502) and the Apple II did share a common video chip in the form of the MC6845, which was a particularly strange beast to program for, but again, the overlap between those two systems was minimal at best.
I wrote code for published games and applications for all of those systems, and more besides like the TI99/4a, including a couple of C compilers.
You know, it is so far in the past now I cannot recall if "The 6845 was only in the Videx cards" is true or not. I suspect you are right and I am confusing Apple's weird video RAM layout with the 6845. Now I need to go check on my old Apple II.
Update: You are correct. It appears I have reached "that age."
The TI 99 had some interesting design choices. The CPU had a very small amount of SRAM, 128 bytes IIRC, because it couldn't easily use DRAMs, which were much cheaper. The BASIC interpreter in ROM would read the program from the VDP's memory (which was DRAM) and interpret it, storing data back into the display controller's memory. It was a really nice 16-bit minicomputer CPU with one of the ugliest hacks around it to make it fit a home computer budget. Legend says IBM almost settled on the TI99's CPU instead of the 8088 for the IBM PC (they also mused about plain acquiring Atari) but didn't go for it because TI would be the single source for the component.
The same VDP would be the basis of the MSX, Master System and a couple others.
The 8 bit Atari design team had a lot to do with the amiga computer. The 16 Atari st series shared a CPU with the amiga, but otherwise was very different.
It is faster but the ANTIC/GTIA steals cycles from the 6502 while the VIC-II cycles are interleaved with the 6502 to greatly reduce cycle stealing: https://www.youtube.com/watch?v=mxi5_VhxkJQ
One other thing they have in common is the lower case font of the C64 is identical to the Atari lower case font. Apparently Commodore stole it but it seems Atari didn't care.
Atari 8-bit and Commodore machines (and Apple II as well) did share a common 6502 CPU, but the coprocessing chips for graphics and sound are really what separated these machines. Apple's capabilities were far inferior, but it also was released years before the others. (If I remember correctly it was 1977, 1979, and 1982 for the Apple II, Atari 8-bit, and C64).
Atari developed three specialized chips for these computers; two for graphics and one for sound, building on what they learned from the original VCS/2600 machine. Programming these machines is primarily a matter of mastering these three chips.
Unlike the 2600 game machine, there was indeed a frame buffer on the 8-bits, and Atari engineers did some really neat tricks to make interesting use of display memory, allowing programmers to display things differently in horizonal strips down the screen, trading off memory usage, pixel size, number of colors, and text display. As a kid playing lots of Atari games back then, you quickly noticed patterns in how the screen was always laid out -- scores and status along the top or bottom, fancy graphics in the middle.
Commodore's entry a couple years later was suspiciously similar in capabilities, but in a massively cost-reduced form. A big leap in sound tech, but a step sideways or backwards in graphics. In junior high we sat at different lunch tables, emotions ran pretty hot on our nerdy brains back then.