I have very fond memories of the ZX Spectrum. By modern, or even contemporary, standards, it's a weirdly under-powered machine, yet it introduced a (mostly "continental") generation to gaming, programming and much more.
The built-in BASIC made the Spectrum very accessible. But it was also quite limited, mostly due to being very slow. But: the great thing was, all the machine code that processed said BASIC was right there, in the ROM, just waiting to be examined.
I still remember disassembling the machine code responsible for handling the "LOAD" and "SAVE" commands, which were an interface between memory and the tape deck (the only long-term storage available). It was surprisingly small and elegant, and easily modified to perform certain tricks, such as varying the baud rate of the cassette interface, the order in which bytes were loaded (allowing for cool effects like "the screen is populated, but not from top-to-bottom, but the other way around), and many other things.
And this was all waaaaay before the Internet, relying on (photocopies of) library books about the Z80 and magazine articles, which arrived late-if-at-all. At some point, I'm pretty sure I had memorized the purpose of every "OS-related" memory location of the Spectrum (all 16384 bytes of it).
The complexity of today's systems makes all of that impossible. But that's mostly nostalgia talking: the capabilities of the Spectrum would be laughed away (and rightfully so) these days.
There was a wonderful book called 'The Spectrum ROM disassembly' that gave a full and detailed analysis of the whole thing. A good chunk of the code was cloned from the ZX81, but as you say the tape routines were very nice, as was the stack-based calculator which was invoked via an RST call followed by opcodes for pushing numbers plus all the arithmetic and trig functions. I got knee deep into my own disassembly of the Interface 1 (?) ROM which has all the microdrive code, but never finished it :-/
Ah yes that brings back memories. I knew that book inside-out.
I made the ROM writable by soldering a CMOS ram chip across the ROM (was it 16KB?) and any write to the ROM would end up in the RAM. A switch selected either the ROM or RAM to read from. On startup simply copy the ROM to the RAM and flip the switch.
After this operation, using 'The Spectrum ROM disassembly' book the world was your oyster. I modified the ROM routines for reading/writing those little tape drives and bypass copy protection, for experimental purposes of course :)
Yeah, that seems to have been a pretty popular book, but I've literally never seen it. At the time, no library near me had it available, and ordering it from the UK was just too expensive for 13-year-old-me. I did have my own ROM disassembly, in two school notebooks, that I still keep to this day. Mu handwriting was pretty bad already then, though, so I prefer to think of all this as "lost in time" anyway.
Decades later, I did (pre-)order and read "The ZX Spectrum ULA", which documents, in painful detail, the inner workings of the custom Ferranti chip that powered most of the Spectrum.
This really did drive home the message that, no matter how much I thought I understood the low-level workings of my Speccy, there were still many lower-level layers left to explore. Which, I guess, is the central lesson of IT...
I had that book and remember learning something from the very first line of code; XOR A. This clears the accumulator (of course) with a one byte instruction, improving on the more obvious LD A,0 two byte instruction I'd always used up until then.
I did a similar thing with the ROM of the VIC-20. I didn't have a printer though. So I wrote out the entire BASIC ROM in 6502 assembly language, longhand, in my school exercise books starting from the empty pages at the back...
My greatest sense of accomplishment came from figuring out how floating point arithmetic worked in an 8-bit processor, and then the sin, cos and tan functions.
I could have a rant about your last line there. I even long for the days of the 00s when web programming was much more simpler albeit a little hairy. The obtuseness of modern js development is obscene and with little sincere justification. I think it's true capabilities bring about some minimum level of complexity but the level of complexity in modern software sometimes seems rather unnecessary.
I sort-of get what you're saying here, I think, but I'm not sure you're right.
As an inquisitive young person, you are, quite likely, at some point confronted with something that seems like magic.
If you're truly (or perhaps excessively?) inquisitive, you try to dissect that magic. Sometimes that leads to true understanding, sometimes just to confusion, or at best the understanding that you don't understand.
The "home computers" of the 1980s were still simple enough to allow "true understanding". But only up to some point: I could find my way around a ZX Spectrum memory map just fine, but could I have built such a machine from scratch? No way!
In hindsight, I only understood a very small portion of the technology I was working with, even though that understanding was absolutely mindblowing at the time. Today, that portion would very likely have been "higher up the stack": let's say, I would be an absolute master of the DOM using Javascript, instead of a master of the ZX Spectrum ROM using Z80 assembly.
But would that portion be less "worthy" or less useful? I'm not so sure...
I don't think GP is talking about JavaScript dom manipulation, i think they are talking about typescript/babel/webpack/esm basically even before nyou start programming in a high level language like js you have to use a bunch of tools that you don't even know how they work, it's just some magic config you set up and cross your fingers.
But maybe I'm reading too much into their post.
I'm a dev of 12 years who cut my teeth on assembly and c, i currently write "modern" js and I feel this way, if it's far too complicated for me, it's going to be even worse for a newbie
Nope, you're 100% on the money. I'm talking about any modern web app's dependencies and the mountain of tooling overhead, it's all so complicated it's hard to really understand completely.
Every desktop browser can drop you into a full-blown, highly interactive IDE at the press of a button. It's far more capable than any 8-bitter ROM BASIC but just as accessible.
I'm talking about the IDE built into the browser. High-complexity tooling, etc is not some inherent property of programming-as-you-can-do-it-on-a-computer-today, just like the simple BASIC environments weren't the only way to program an 8 bit computer of yore. You could definitely make it much more complicated for yourself if you wanted or needed to.
There was an enterprising coder who would sell a Basic compiler the related Timex 2068 computer.
It had lots of limitations, such as only allowing one dimensional arrays, but I was able to use it to implement Conway's Game of Life which I let run for days on my CRT TV.
It's easy to quibble about some aspects of the Speccy - the rubber keyboard or the limited BASIC for example - but the key thing is that it offered an awful lot for the price - starting at £125 in the UK when the cheapest BBC Micro was £300.
This made computing with colour and enough memory to write programs that were substantial and interesting available to a much wider group than before.
Sir Clive Sinclair had a unique genius for designing and then marketing products that caught the public imagination. Sadly, he seemed to lose interest in building on his success and quickly moved on to the next project. Famously the C5 electric "car" but also wafer scale memory! [1]
If anyone hasn't seen Micro Men, on the Sinclair vs Acorn rivalry, its definitely worth a watch:
My first computer was a Spectrum 48k. My school bought a ZX81 and a logo turtle - one for the whole school. We went down as a class and got to play with it a group, calling out instructions that the teacher would type in. Other kids seemed to get bored with it quickly, but I was hooked.
At home, I went on and on about this to my parents.
My mother had done punch card work in University so recognized how big of a leap it was to be able to have a computer in the house. A few days later they announced that we would get one.
This was in Asia, and the Spectrum 48k had just been released there. Games rarely made it all that way, but the magazines did, so I spent hours upon hours typing code in, bug fixing, modifying things here and there. Save it to cassette tape. I still have dreams where the sound of software loading from cassette appears - kind of like the sound a modem makes connecting, but longer and somehow softer.
Every few years we'd go on holiday to the UK and I'd save up my pocket money to buy as many games on cassette as I could. Then I'd spend the rest of my holiday reading and re-reading the inserts, trying to imagine what the game would be like when I finally get it home. Titles like Ghostbusters, Dungeon master, The Hobbit, Zzoom, Chess, Horace and the spiders, there was even a 3d maze with skulls and jewels. It wasn't all good through - I waited weeks to play Cookie only to get home and find the cassette didn't load properly!
But the most time I spent was trying to write my own games in Basic. It was amazing - a machine with everything you needed right there, a language, colours, sounds, all built in, ready for a young mind to explore. The keyboard even had the keywords and colours printed on each key and the editor knew when to expect a keyword rather than a letter. The whole of Basic was right there in front of me to explore without having to read through thick manuals.
After a while the 128k came out, and the new games no longer worked on my lowly 48k machine, and as my cassette tapes started to wear out or worse (where I lived there was one particular insect that liked to make little clay nests in cassette tapes...). Soon I was a teen and more interested in meatspace than the gaming world, but that early programming experience informed so much of my life and career.
Fond memories. Thank you, Sinclair, for opening up a whole world to me.
Semi-related, I once opened the case of my DVD of Blade Runner to find a whole nest of ants inside it, complete with tiny eggs. I didn't ask who was the queen and, without much respect for any royalty, killed them all. To this day I wonder what on earth did they find so appealing about my DVD...
Probably a wasp or solitary bee of some sort. We never saw the insect, just the little nests in some tape or book spine you hadn't opened for a while. Insects, spiders, centipedes, lizards, all had pretty much free range in the houses back then. Every once in a while one of our cats would run up the walls trying to catch something.
Years later in Canada, I opened up an old amplifier we'd brought back with us to see if I could get it running again, and inside was a mummified gecko, perfectly dried, sitting on the board. They were constant companions on our walls, keeping the house free of the moths and mozzies.
I think this gets some of the Spectrum experience, and misses other parts.
It was never really an open system. The firmware was closed source (you could eventually buy an unofficial disassembly) but you couldn't update it with your own changes. You could add external hardware, with some effort, but it was never trying to compete with a backplane system like S-100.
What it did have - apart from very low initial cost and wide availability - was instant-on (no formatting, no setting up, no downloading and installing), staged progress from beginner to expert (i.e. from BASIC to assembler), a small comprehensible system (the manual explained everything BASIC could do, assembler needed an extra book or two but was still very manageable) a very large market with very low cost of entry and high margins (you could write a game, advertise it for almost no money, and send out the initial copies from home with no duplication costs), and a supportive culture of print magazines, occasional TV news and documentaries, and computer shows. (Face to face clubs were much rarer and less influential.)
The physical case design was just plain cool. And it worked with your own TV, which was almost like being on TV.
So basically a combination of instant gratification, tiny-system simplicity with tough constraints that rewarded clever solutions and creativity, low-friction financial opportunity, cultural reinforcement and support among peers working at a similar level, distinctive aesthetics with a coolness of a sort, and affordability.
I don't think it's a coincidence that it happened not long after punk and synth pop in music. Even if their output was very different, all of of those had very similar cultural features.
I made the ROM writable by soldering a CMOS ram chip across the ROM (was it 16KB?) and any write to the ROM would end up in the RAM. A switch selected either the ROM or RAM to read from. On startup simply copy the ROM to the RAM and flip the switch.
From there on you can read/write the original ROM and modify it to your hearts content.
How did this compare to the Commodore 64? A few of the details are similar it sounds like, (instant-on, a small comprehensible system although with a bunch of add-ons). I guess the c64 wasn't as cheap.
Price! C64 cost £399 at launch, while the top of the line Spectrum was £175 (and there was a cut-down model for £125). In today's prices it's around $500/700 for the Spectrum vs $1600 for the Commodore. And the UK was considerably poorer than the US in the early 80s too. The Commodore certainly did more, but entry price really mattered.
Thanks, I couldn't find a usd dollar amount for the spectrum. I did know the c64 cost $1600 in today's prices (that's a good self-built pc today, not quite gamer specs but still decent)
The Spectrum wasn't released in the US. However, the semi-compatible Timex-Sinclair 2068 mentioned by others was. It was quite cheap, selling for under $200 in 1983 (about $570 today). However, it got very little support and software in the US and so it didn't do well.
c64 famously had its price cut very aggressively multiple time shortly after introduction, as commodore tried to drive texas instruments out of the home computing market (they succeeded, with atari and the rest of the industry becoming collateral damage). I believe not even a year later it cost half as much.
Very similar. The C64 hardware was better, with a dedicated audio chip, better color and (IIRC) hardware blit support for sprites. Much better keyboard, too.
But it was double the price, putting it out of reach for many more families than the Spectrum. This made a kind of critical mass that lead to a huge community around the spectrum in the UK. And a fantastic burst of creativity as the barrier to entry to writing video games dropped as low as it would ever get.
Similar to the Atari's. And they both offered redefinable character sets and fine scrolling, which allowed you to create giant scrolling maps and backgrounds as screenfuls of characters requiring very little memory.
The C64 was much more game-ready out of the box, with a joystick port, an excellent sound chip and hardware sprites. Also I think the C64 had a decent disk drive available at launch, which the Spectrum never really got one of.
Perhaps the best thing about the Spectrum was that the manual, which documented the built in BASIC programming language and also the Z80 asm opcodes.
Edit: I should probably steer clear of culture war topics but let's be honest - the designers cut every corner they could think of and consequently the Spectrum looked and sounded atrocious compared to the luxurious C64. But I probably do owe my tech career to one.
Yes, the C64 was more expensive (at least early on, when the exchange rate was not in its favour), but also, Sinclair's BASIC enabled use of all the graphics and sound features - even if they weren't as sophisticated as the C64, they were at least accessible without PEEKs and POKEs.
The C64's BASIC really frustrated me as a kid. Now I understand there were license and "being a cheapskate" issues regarding the lack of a newer BASIC version, but imagine the even bigger impact the C64 would have had if most of its features had been available via advanced BASIC statements other than PEEK and POKE.
I used the C64 only for games, and the spectrum for my own programs and the odd top game
and yes I was on both sides in the playground,
but the C64 had something missing that the spectrum had, hard to put a finger on it, the spectrum did have inferior games (based on the specifications), but It was more accessable or hackable (in todays speak)
I'd say the spectrum kids was more into modding it, typing their own code from magazines and learning stuff, but the C64 kids used it more like console. and could not see the reason for having a spectrum (due to the inferior spec etc..)
I didn’t do any speccy hacking, but the C64 was IMO amazing in the regard. The way you could reprogram the VIC each horizontal line into different video modes, changing the screen width to make borders disappear, the way you could disable the kernal ROMs to expose more DRAM etc.
But all machines of that era were so low level with plenty of tricks to exploit.
yes the C64 had some very cool features, I tried to develop some basic games on it using sprites. but it felt like an uphill struggle. I remember making cool music was easy tho
maybe it was the school I went to and the information the collection of kids had
I was twelve when I got mine. We first had a 16k spectrum on loan from the primary school where my mom was a teacher -- together with a hefty course in Informatics from the Dutch LOI training school. When the little chap had to go after a month, because another teacher needed training, I was inconsolable. Shortly after, we got a _48_k spectrum, because I already had showed I could code up stuff on the 16k one.
I had to work for it, though! I had to raise my score for English from 3/10 to at least 7/10, or no speccy. Fortunately, all sinclair magazines were in English, so by Easter I had scored 10/10!
And after that... I coded, I gamed, I read books, bought extra programming languages, coded, gamed -- and by the end of my high school career, its keyboard had died.
The empty shell hangs from a picture hook in my study, to remind me of where I came from, and also, because I have always loved its gorgeous design.
(Weird to think that the speccy sold 5 million units or so... Which is about the number of people using my open source application Krita every month, too.)
The speccie certainly helped kickstart my computer science career. Sinclair BASIC made for a friendly programming experience, and once outgrown, I enjoyed learning the intricacies of Z80 programming. Even the attribute color system where each 8x8 block of pixels had one dedicated color byte including a foreground color, background color, and I think brightness and flash bits, proved very charming when I programmed a connect-4 game using attribute memory as storage for the board. You could literally see the alpha-beta game tree search progress through the screen colors.
Some of my favorite games were Lords of Midnight, The Sentinel, and Underwurlde. Good times...
My personal-favourite was "Chaos: The Battle of Wizards", by Julian Gallop. I still play that every few months under emulation. There are modern sequels and remakes, but I've avoided them lest I be disappointed!
But there were lots of great games, the Dizzy series, RoboCop, Strider, R-Type, and many many more.
> But there were lots of great games, the Dizzy series, RoboCop, Strider, R-Type, and many many more.
There was also the peculiar experience that the Spectrum version of a game would often be more playable or essentially faithful to its arcade parent than that of platforms with more power (even the C64).
Because the Spectrum developers had to work hard to make the game playable in essentially monochrome, with nearly no sound. There is no better way to make art than through constraints, and the Spectrum was all constraints.
All 8-bit systems benefited from this art-through-constraints situation, though, and gaming culture owes everything to it. This could be why I am more inclined to play a cartoon MMORPG like Dofus than anything else; if a games designer is unwilling to choose their own constraints I am going to find the game uninteresting.
[Edit to change last sentence: wrong choice of words]
The Sinclair home computers (ZX80/81 and Speccies) were probably the main inspiration for most Eastern European hobbyist computers, because (unlike the C64, CPC or Atari 400) the hardware was simple enough that it could be built with relatively cheap domestic chips and standard TTL logic.
Throughout 1982 I begged my parents for a ZX Spectrum, after reading all about it in the computer magazines we had in our public library for months.
On Christmas morning, I woke up to a BASIC program running on the TV screen welcoming me to my brand new TI-99 4/A. Probably a better choice for us as I don’t think I knew anyone else in the US with a Spectrum.
I still have the TI, it’s upgraded to HDMI output using an FPGA replacement for the display processor, and has all the software ever released for it installed on one cartridge. Fun to break it out when the family gathers for holidays. There’s even some modern game development going on that really shows how capable the old hardware was, but was limited by primitive software development tools and practices.
On the modern game dev around 80's machines, there is a sort of rebirth of 80's computing lately. I was born in the 90's but I learned 6502 asm to make an NES demo and now this thing is a hobby of mine. Since it's the same cpu (albeit pretty different arch) I'm learning about the C64 too now.
It sounds like the TMS9900 has a very different architecture with the workspace idea although it looks like the ti-99 4/a only allowed you to do this scheme with only 128 words. The idea itself sounds pretty cool.
A bit of advice: never let go of your TI. You'll regret it after a few years, when nostalgia and the urge to turn it back on strikes again.
It happened to me as a middle aged guy when I remembered the C64 my dad sold in order to buy me my first PC XT.
That's why I ended up buying a retro clone of my cherished C64, TheC64. ARM-inside running VICE, but it looks and behaves a lot like a real C64. It has a real keyboard and you can use it to program, not just run games.
A decade later but the games I had growing up for the N64 and gamecube now cost a pretty penny. I've learned now to buy the best games for modern systems physical because in 2040 I don't want to have to pay $200 to play metroid dread
I had both a Spectrum (actually the Timex-Sinclair 1000) and a TI-994/A. The TI was a lot more capable, but having the Spectrum first was a good gradual learning experience. I think it was a great way to get into computing and gain the lifelong attitude that the computer does what I tell it, not what someone else thinks it should do for me.
The Timex-Sinclair 1000 wasn't a version of the Spectrum -- it was instead a version of Sinclair's previous machine, the ZX-81. The 2068 was the Spectrum-based machine. The ZX-81/TS 1000 was B&W and had no graphics (other than what could be created by special characters). The Spectrum/TS 2068 had color and graphics.
Hate to nit pick but... the Ariston advert used the C64's version of the Robocop theme (slowed down a bit) - not the Speccy's as the article implies. Maybe it was originally composed on the speccy?
I got a cheap Vic20 when I was wee, so I never thought much of the rubber doorstep and was never a fan of Sinclair as he was seemingly some aristocrat who was gifted a commercial niche below the BBC Micro (as bbc/acorn didn't bother making a budget model until the slightly borked Acorn Electron). But in recent years I notice that the Spectrum demo scene has become fantastic, in artistry and possibly superior in code wizardry to the C64s own bedazzling competition. The retro Spectrum scene is producing surprising games and a game capable multicolor mode was even invented a few years back which was truly unimaginable back in the day. More groundbreaking than late c64 inventions. So fair dues neighbor... but come off it, speccy music in a big TV advert?? :}
I ended up restoring and modding 2 Sinclairs just now (regular speccy and the plus version). I remember it was much easier to enter programs as a kid. Now my muscle memory in front of a keyboard is working against me. Fast typing is frowned upon. Still, despite all that, what a glorious piece of hardware.
It's almost impossible to understand how minimal and spare of a design the Speccy was. Yet it fostered a creative community that produced literally thousands of titles. It's something of a lesson in how you don't need the most powerful computing device to do great things.
What can I say? In 1985, my parents went on an organized tour to Munich (it's not like they could've went on their own) and bought a deeply discounted Speccy and smuggled it -- it's not like we could've afforded a computer any other way. At the same time, they sent me to a computer-focused summer camp at the nearby community center. Of course, some of it was just playing video games but some of it was learning BASIC, also on ZX Spectrum machines. I was ten.
I am 47. I am still coding. It's not BASIC but still. In my niche, I have become one of the world's top for doing what I do and I am paid far beyond anything that ten year old in socialist Hungary could've dreamed of. Not that boy had a lot in dreams beyond the fierce desire to live a different life... I wrote that up just two months ago https://news.ycombinator.com/item?id=29681279 Ironically, I still live in a concrete high rise built in the early 70s but a Vancouver high rise on the shores of the English Bay is slightly more livable than a Hungarian microraion.
Thanks Speccy for giving me the opportunity. I ran with it.
My ZX Spectrum was an upgrade from a ZX-81. I had the thermal printer and a microdrive at some point. I have a few microdrive cartridges still sitting around right here (I still have my Speccy and the microdrive as well).
Fond memories trying to write some simple programs, working around the various limitations. Monopolizing the family TV, sitting on the carpet in front of it tinkering with things...
Lots of games, lots of pirating (copying tapes around). I did actually buy a couple as well ;) Playing or programming with other friends that owned Spectrums (and some rivalry/jealousy with the guys with Commodore's or Apple II's).
Brilliant machine, sadly unsupported. Had built in sound via an AY-3-8912, two Kempton compatible joystick ports, a cartridge port and extra high resolution modes. Plus an incrediably cool case. If you were determined you could get a Spectrum rom cartridge to turn it into a Spectrum, a twister board and even hookup micro drives...
I never had a Spectrum, but it's easy to understand the magic of such a device.
It's tiny, it's relatively cheap, it's simple enough to take apart (disassembled ROM, or dis-assembled hardware I suppose).
Sure, it was underpowered, and the keyboard was cheap. But for a kid, those can be features.
My first computer was a relatively luxurious TRS-80 Color Computer. My family could almost afford the 16KB version. It was a technically clean design, and I learned a lot, and here I am.
Give a kid a tiny machine, some documentation, and tell them it is theirs.
I was luck to have had a number of computers that were essentially "mine". First a ZX Spectrum, then the +2A, an ancient Compaq luggable (which had the most wonderful keyboard), and an ancient Toshiba laptop. The fact that these were mine to do what I wanted with, without worrying about breaking them, was really important in giving me the freedom to really explore them.
The Spectrum was first a very beautiful object thanks to Rick Dickinson. And, as a side note, he proved with the Spectrum Next, he still have all his talent.
Frankly, to have this object at home in the 80 was classy! A work of art.
And for me it's what define the Spectrum. The main games were not the most beautiful but had a very distinctive and enjoyable touch. A tiny machine but which a lovely and specific spirit. It was a so nice time in my memory.
Timex Sinclair, the U.S. version of the ZX Spectrum pretty much my all-time fave, other than perhaps Tandy's CoCo and for similar reasons -- both did unique things to make it possible to get useful compute done. Probably slight edge to the CoCo with the peek / poke turbo option
My only "spectrum" was a paper one - a keyboard drawn from a magazine pic. Now you know there's something worse than a rubber keyboard!
Never got the real thing though, ended up with Atari 800XL, better comp in many aspects but pretty rare thing in 80-ties ex YU.
Great machine. My first program was written on it, at an age of 10. It was an animation of a flying bomber that dropped a bomb - and to do that I learned how to redefine sprites, encoding bits in hex!
If you genuinely want the real thing, the best bet is to learn how to restore them. There's a whole network of Youtubers who teach people how to restore them[1], but you'll need basic electronics and soldering skills. Beware that even once you've obtained/fixed a ZX Spectrum, they won't work with modern TVs or monitors. There's a simple mod for composite output, but that means you have to find something with composite input. And they're quite frustrating to use (I say this as someone who owns two! including the legendary "toastrack" Spectrum 128K)
If you just want a taster and/or to play games then I'd go for emulation.
There is even a community spectrum next computer that is fully compatible and then extended. Seems to be popular with people who want to code for nostalgia. I’m more of an c64 and amiga head and have my eye on the vampire v4 as it seems like it scratch the nostalgia itch and could even be useable for general computing.
The experience on an emulator is not always 100% accurate. Sometimes the small lag added can change the gameplay feeling considerably and there might be tiny differences in the sound and the colors. I would suggest you to look for an FPGA replica. An N-go board or a ZXUno is a very reliable replica of the original hw for a decent price. If you have more money to spend then try to purchase a used ZX Next. If you do not care about such finesses then go for emulation though.
The built-in BASIC made the Spectrum very accessible. But it was also quite limited, mostly due to being very slow. But: the great thing was, all the machine code that processed said BASIC was right there, in the ROM, just waiting to be examined.
I still remember disassembling the machine code responsible for handling the "LOAD" and "SAVE" commands, which were an interface between memory and the tape deck (the only long-term storage available). It was surprisingly small and elegant, and easily modified to perform certain tricks, such as varying the baud rate of the cassette interface, the order in which bytes were loaded (allowing for cool effects like "the screen is populated, but not from top-to-bottom, but the other way around), and many other things.
And this was all waaaaay before the Internet, relying on (photocopies of) library books about the Z80 and magazine articles, which arrived late-if-at-all. At some point, I'm pretty sure I had memorized the purpose of every "OS-related" memory location of the Spectrum (all 16384 bytes of it).
The complexity of today's systems makes all of that impossible. But that's mostly nostalgia talking: the capabilities of the Spectrum would be laughed away (and rightfully so) these days.