[HN Gopher] How Apple's developers reflashed Mac ROMs in the '90s
       ___________________________________________________________________
        
       How Apple's developers reflashed Mac ROMs in the '90s
        
       Author : SerCe
       Score  : 177 points
       Date   : 2023-11-27 08:11 UTC (14 hours ago)
        
 (HTM) web link (www.downtowndougbrown.com)
 (TXT) w3m dump (www.downtowndougbrown.com)
        
       | rbanffy wrote:
       | From the color scheme, I assume the author of the utility really
       | liked Squeak.
        
         | ahoka wrote:
         | Actually the UX of that app is just awesome.
        
         | pavlov wrote:
         | This is actually older than Squeak by a couple of years at
         | least.
         | 
         | The reason why so many early 1990s UIs have this kind of color
         | scheme is part fashion and part technological opportunity.
         | 
         | Rainbow pastel colors were really popular around 1986 - 1993.
         | It was a reaction to the muted browns and oranges that
         | characterized '70s and early '80s design, and also a reflection
         | of the economic optimism of the era.
         | 
         | At the same time, computer displays evolved beyond monochrome
         | (original Mac) or garish 16-color palettes (PC EGA). With 256
         | colors out of a palette of millions, it became possible to
         | display those fashionable pastels on a computer too. So why
         | hold back?
         | 
         | (Personally I'm still stuck in this era. Light background is a
         | must. I never use dark mode on anything. I genuinely don't
         | understand the kids who want their IDEs in black like some
         | depressing 1982 textmode VAX. For me it's warm pale yellow and
         | baby blue terminals all the way; extra bonus for dark purple
         | text highlights and a mint green pique shirt.)
        
           | tralarpa wrote:
           | > The reason why so many early 1990s UIs have this kind of
           | color scheme
           | 
           | Do you have any examples? Because from the early 1990s I only
           | remember Windows pre-XP (mostly black and white and blue),
           | AmigaOS (mostly gray, including the newer frameworks like
           | MUI), NeXTStep (gray). Only exception: the colored tabs in
           | OS/2 Warp, if I remember correctly.
        
             | fidotron wrote:
             | SGI Irix is a good case
             | https://en.m.wikipedia.org/wiki/IRIX
             | 
             | It is the windows 3.1 aesthetic on much more capable
             | hardware.
        
               | tralarpa wrote:
               | Thanks. But I was looking for something like the flash
               | tool shown on the website, or like the default color
               | scheme of Morphic. "Crazy" colored GUI elements etc., not
               | just the background.
               | 
               | Edit: never mind. The link by pavlov has more examples.
        
             | pavlov wrote:
             | SGI IRIX is a pastel-land which I'm very fond of:
             | 
             | http://toastytech.com/guis/irix.html
             | 
             | It's more muted, but follows the principle of "let's use
             | these truecolor hues now that we've got them."
             | 
             | The global fashion trend after 1990 was moving away from
             | bright pure colors and towards increasingly muted pastels.
             | So for examples of more bright-colored UIs on 256-color
             | displays, I think the Mac II / System 6 era would be the
             | place to look. Early CD-ROMs might be a rich vein.
        
             | actionfromafar wrote:
             | AmigaOS 1.3 and earlier was bright blue, white and a
             | sprinkle of orange.
        
             | noelwelsh wrote:
             | Windows 1.01 goes hard on the vibrant pastels:
             | https://guidebookgallery.org/screenshots/win101
             | 
             | It's a reflection in UIs of Memphis Design, which dominated
             | the 1980s: https://en.wikipedia.org/wiki/Memphis_Group
        
             | einr wrote:
             | CDE: https://upload.wikimedia.org/wikipedia/commons/a/ae/CD
             | E_Appl...
             | 
             | CDE had different default color schemes from different
             | vendors but most of them were pretty colorful in pastel
             | hues.
        
           | diegoperini wrote:
           | > Personally I'm still stuck in this era. Light background is
           | a must. I never use dark mode on anything. I genuinely don't
           | understand the kids...
           | 
           | Kid here (34). My understanding is our generation grew up
           | spending much more time looking at a screen in general.
           | Gaming, socializing, following news, doing work, doing
           | homework, talking to parents, talking to partner(s), reading
           | books, painting, sculpting, paying taxes, managing finances,
           | applying jobs, applying for visas... The list is too long to
           | fit here. Participating in society demands more screen time
           | than ever.
           | 
           | Dark mode makes screens blend with the environment better by
           | emitting light where only needed. Since we can't reduce our
           | screen time without any compromise, we try to optimize with
           | the dials we are left with, in this case, pixel brightness.
        
             | pavlov wrote:
             | My personal theory of display ergonomy is that a light
             | background is better for the eyes because then you have to
             | dial down the screen brightness all the way to a level
             | that's good for reading (generally something close to paper
             | white in the same environment, and usually much lower than
             | the display's maximum brightness).
             | 
             | Admittedly this theory is only backed by personal
             | preference and some vague recollections of CRT-era
             | ergonomics discussion in 1990s UI design books.
        
               | diegoperini wrote:
               | > Admittedly this theory is only backed by personal
               | preference
               | 
               | Same for my argument too.
               | 
               | There is also the cultural factor. The age when I was
               | going to make a decision about which high school to
               | choose and what kind of study to pursue, we had the
               | chance to enjoy the release of a few of the best sci-fi
               | movies/shows ever made. Those movies had the black
               | screen, neon green/blue strokes and fonts as the main
               | design language. Looking at the letters falling down in
               | the movie Matrix, it was like "coooool, I wanna be able
               | to type those in real time and make computer do stuff".
        
               | simfree wrote:
               | Lots of us younger people have dark mode with the screen
               | brightness turned way down. I personally often have my
               | screen brightness at minimum, and on mobile I have Extra
               | Dim turned on for more than half of my usage time.
        
               | pavlov wrote:
               | OTOH reading too low-contrast text is supposed to be bad
               | for the eyes too? (At least that was what parents and
               | educators told me as a kid: "Read at your desk where the
               | light is good or you'll spoil your eyes!")
        
               | pasc1878 wrote:
               | And us older folks have screen brightness turned up as
               | our eyes get worse. For many years I had white background
               | so I could really see things.
               | 
               | Now with floaters I have to use dark background and many
               | games are now unusable as they have light background and
               | medium unreadable text and strain my eyes.
        
               | bitwize wrote:
               | No, it's backed by evidence. Light mode is, objectively,
               | better for your eyes because light characters on a dark
               | background tend to "bloom" and be less clear.
               | 
               | https://www.nngroup.com/articles/dark-mode/
        
             | blincoln wrote:
             | I'm in my mid-40s, and I've been looking at screens for
             | many hours on most days for about 38 years. I've preferred
             | a "light mode" colour scheme, with the brightness cranked
             | up ever since I first saw one (an original Mac that a
             | friend's parents bought in the late 80s).
             | 
             | My personal theory is that some people are just genuinely
             | more light-sensitive than others, but that the main factor
             | is which scheme came (back) into fashion during someone's
             | formative years, so it will always be associated with being
             | new and novel to that person.
        
           | executesorder66 wrote:
           | In matters of taste, I like both light and dark mode equally.
           | 
           | In terms of practicality:
           | 
           | - Dark mode uses less energy and doesn't burn your eyes at
           | night.
           | 
           | - I've only ever found light mode useful when the ambient
           | light is really strong, e.g. direct sunlight shining on my
           | laptop screen. When this happens dark mode is basically
           | impossible to read even with full screen brightness.
           | 
           | So 99.9% of the time dark mode will suit my needs better.
        
             | slowwriter wrote:
             | Yes, on an OLED panel dark mode saves energy, but not on,
             | say, an LCD panel
        
               | semi wrote:
               | I could be wrong but I think it's only saving power if
               | pixels are actually solid black where the pixel can be
               | turned off entirely. I don't think dark shades are more
               | power efficient than other colors. Thankfully a lot of
               | apps are getting explicitly named OLED dark modes to take
               | advantage of that.
        
               | nomel wrote:
               | It would have saved a negligible amount on a CRT monitor
               | of the time, as well.
        
           | qball wrote:
           | >Light background is a must. I never use dark mode on
           | anything.
           | 
           | Dark mode is fundamentally a hack around two things.
           | 
           | First, shitty screens that can't run light mode anywhere near
           | dim enough once the sun goes down (which is at least a
           | 5-nines percentage of all screens ever produced). A good
           | chunk of this is due to insufficient PWM frequency but
           | software has a lot to do with it too- and if I can't make the
           | screen go dark enough, well, _then I 'll just tell all the
           | pixels to be black and use white text_.
           | 
           | Second, shitty flat UI design has made it more difficult to
           | see borders between items. It seems to be easier to pick out
           | a bright glowing spot in a field of black than the reverse-
           | it's worse for comprehension, but not for
           | identification/differentiation. It's easier to see _that_
           | something is selected when you 're using white-on-black, and
           | if you already have a good idea what that something is the
           | comprehension penalty is irrelevant.
           | 
           | Those two things predate most proper dark mode
           | implementations; I assert they created the need for it to
           | exist in the first place.
        
             | NikkiA wrote:
             | Bright displays also absolutely fuck up my ability to focus
             | my eyes for the rest of the day, so I attempt to use dark
             | themes on everything, having to accept a light theme for
             | any site or OS feels like a personal failure and reminds me
             | of my almost-useless old eyes.
        
       | HeckFeck wrote:
       | > By the way, I actually succeeded today at hacking the code of
       | Flasher to erase and program modern flash chips. It required a
       | lot of 68k assembly work, but luckily I had a good reference to
       | start from in my USB SIMM programmer.
       | 
       | And then, jealousy intensified, I close the tab and go back to
       | debugging my MVC webapp.
        
         | TazeTSchnitzel wrote:
         | Why be jealous and only feel bad about it? Let the envy
         | motivate you to create great things! There are a million tiny
         | hobby project ideas out there that you have the power in your
         | hands to actualise.
        
           | blincoln wrote:
           | You never know where such things will lead, either. I did
           | reverse-engineering as a hobby for years because it was a
           | personal interest, then eventually switched careers to
           | information security partly because of that background.
           | 
           | No one is ever likely to make a living reverse-engineering
           | 30-year-old ROM-flashing utilities, just like no one is
           | likely to make a living figuring out how to convert
           | early-2000s console game data to standard formats, but that
           | kind of hobby project builds skills that are uncommon and
           | useful in certain lines of work.
        
             | rmilk wrote:
             | Precisely. I have been told I have a knack for reading
             | other people's code. Turns out it was years of reverse
             | engineering as a hobby in my youth that gave me the skills
             | to sit down and understand someone else's code very
             | quickly. A hobby that gives useful real-world skills.
        
         | Waterluvian wrote:
         | Two facts I have discovered over the past 11 years:
         | 
         | 1. There are always people far brighter than the people who
         | wrote most of what we use every day.
         | 
         | 2. You are far more capable than you realize.
        
         | surajrmal wrote:
         | The grass is always greener. Working on low level things has
         | lots of drawbacks and it's not uncommon to wish for better
         | tools, documentation, libraries, etc like you get in higher
         | level programming. It takes a lot of work to accomplish what
         | externally seems like trivial results.
        
       | rob74 wrote:
       | I know there's a rule against posting titles like "How To Do X"
       | in https://news.ycombinator.com/newsguidelines.html, but in this
       | case the title doesn't make sense without the "how" - of course
       | Apple's developers reflashed Mac ROMs in the 90s, they had to do
       | it as part of their job, the article is about _how_ they did it.
        
         | appleskeptic wrote:
         | You're misreading the rule. Such titles are allowed.
         | 
         |  _If the title contains a gratuitous number or number +
         | adjective, we 'd appreciate it if you'd crop it. E.g. translate
         | "10 Ways To Do X" to "How To Do X," and "14 Amazing Ys" to
         | "Ys." Exception: when the number is meaningful, e.g. "The 5
         | Platonic Solids."_
         | 
         | Just the relevant bit:
         | 
         |  _translate "10 Ways To Do X" to "How To Do X"_
        
           | bragr wrote:
           | I see you've never submitted anything. I suggest you try a
           | few times, deal with the automatic title mangling, and then
           | come back and tell us how you feel about this rule ;)
        
           | dylan604 wrote:
           | It's such a dumb rule to even have. If the article shows 10
           | Ways To Do X, then it is pretty accurate. How To Do X sounds
           | like there is one way to do it, and it's being shown.
           | 
           | What happened to the don't editorialize rule, because that's
           | exactly what's being done in the provided example. You're not
           | just shortening an acceptable length title, but you've
           | changed the meaning.
        
         | airstrike wrote:
         | Submitters can edit titles after they submit a story, even in
         | these cases AFAIK
         | 
         | Also "How X" != "How to X"
        
         | mistrial9 wrote:
         | here in California there were zero instances of "flashing a
         | ROM" among ordinary developers -- it was obviously illegal
         | (maybe a reason) but also you just buy a Mac and get the rom
         | image.. Macs were everywhere... fifty percent of the Macs in
         | the world were in this area, by some measures at some time.
         | 
         | This was the nightmare of Apple from the early days and they
         | actively pursued it. Also, intelligent people in the creative
         | professions were inventing things.
        
           | Clamchop wrote:
           | Why was it illegal?
        
             | KerrAvon wrote:
             | I think the poster (maybe someone's AI experiment?) is on a
             | tangent about replacing the standard Apple ROMs with your
             | own versions? That wasn't really a thing, but it wasn't
             | illegal either. What was illegal was copying Apple's ROM
             | code to sell in your own clone machines.
        
               | mistrial9 wrote:
               | > maybe someone's AI experiment?
               | 
               | if you take half-a-second, longer than I spent reading
               | that article, you would know this is a personnel account,
               | right? do you need to repeat "AI" rumors here ? It is
               | neither amusing nor adding any substance to the topic
               | IMHO
        
           | dev_tty01 wrote:
           | Hmm. You seem to be railing against something that is not
           | related to the article. The article describes how Apple
           | internal developers reflashed ROMs while developing the
           | firmware for new prototype computers. This is something that
           | Apple's developers had to do on a regular basis.
        
             | mistrial9 wrote:
             | yes - my fault.. so it goes
        
       | kragen wrote:
       | is this the actors carl hewitt (rip)?
        
         | CharlesW wrote:
         | This Carl Hewitt is alive: https://www.linkedin.com/in/carl-c-
         | hewitt
        
           | kragen wrote:
           | aha, thanks
           | 
           | not sure why my comment is downvoted to -3
        
             | CharlesW wrote:
             | My guess is that the downvoters think you're talking about
             | an actor rather than the computer scientist:
             | https://en.wikipedia.org/wiki/Carl_Hewitt
        
       | Reason077 wrote:
       | > _"See that thing that suspiciously looks like a CD-ROM drive on
       | the left? It's not. It's a blank cover ... I pressed the button
       | thinking the CD tray would come out. If you push the button hard
       | enough, it gets stuck back in there."_
       | 
       | Pretty weird and un-Apple-like to have a physical eject button at
       | all. The mid-90s were such a weird time to be alive.
        
         | sjsdaiuasgdia wrote:
         | I really enjoyed the handful of mid-90s Mac models where the
         | power button was just to the bottom right of the 3.5" floppy
         | slot, very near where you'd find the eject button relative to
         | the floppy slot on pretty much every PC of the era.
        
           | morsch wrote:
           | It's hard to describe just how _cool_ the soft eject
           | mechanism was. At least to my young impressionable mind. I
           | can still remember the sound it made. It made PCs appear
           | archaic.
        
         | weinzierl wrote:
         | It was in the mid-nineties and I had to hand in my weekly lab
         | report. As my printer at home had decided to go on strike once
         | again (as they used to do in the mid-nineties) I decided to
         | print it in the university's library. So I went, still a
         | quarter to the deadline, with my little 3.5 inch floppy disk.
         | All the PCs were taken so I resorted to the only Mac.
         | 
         | I was a little excited, because these jewels were expensive
         | back then, and usually always taken by someone that seemed to
         | have more important design tasks to do than I had. Now I had
         | the opportunity, for once.
         | 
         | I inserted my floppy, opened the document, sent it to the
         | printer. All went fine until I wanted to get back my disk to
         | rush to the lab session. No button to eject, nowhere to be
         | found, so I asked one of my fellows sitting at a PC. He told me
         | to drag the disk into trash bin. Yeah, right, sure I believe
         | that! So I asked another guy, and sure he said I should throw
         | my disk into the bin.
         | 
         | Now, these lab reports were important, because you needed to
         | pass all of them to be allowed to write the test at the end of
         | the semester and there were only two substitute dates. So I had
         | little choice. I dragged the little disk icon over the little
         | bin icon and let go. I already saw all my work on the disk gone
         | but to my great surprise the disk ejected immediately and
         | completely unharmed.
         | 
         | My lab report was handed over in time, it passed. The two
         | substitute dates at the end of the semester never materialized
         | because the prof was sick, as every year before and after - as
         | I lerned. So, good on me to trust my fellow students but
         | g00daxxit terrible UI!
        
           | benjaminpv wrote:
           | Decades late, but they could have told you to use Special:
           | Eject Disk if dragging to the trash was too much for you.
           | Then you'd have to grapple with what to do now that the
           | physical disk was in your hand but its icon remained. There
           | was also...Command+Y, I think?
        
           | filchermcurr wrote:
           | To be fair to the UI, there's also an 'Eject' option in the
           | menu bar when you've selected the disk. There's also a
           | keyboard shortcut. Dragging it to the trash is just more fun!
           | 
           | Actually, if memory serves, dragging to the trash was a
           | shortcut for ejecting AND... what did they call it... putting
           | it away, I think. Normal eject would leave a ghost of the
           | floppy disk so when you inserted another one, you could copy
           | from one floppy to another. You had to 'put away' to remove
           | the ghost.
        
             | wolfgang42 wrote:
             | The Mac had a distinction between "Eject" and "Put away"
             | mostly as a relic of the days when it had a single 400k
             | floppy drive, so "ghost" disks were used to keep track of
             | however many disks you needed to juggle whatever task you
             | were doing. For example, you'd boot the computer, eject the
             | System and insert your application, start it, then eject
             | the application and insert your document; the system would
             | know about all 3 disks, and whenever it needed something
             | off a different disk it would automatically eject and
             | prompt you to "Please insert the disk: <<Name>>".
             | 
             | In this world, the split makes perfect sense: you eject a
             | disk when you want the drive slot to be free, but you don't
             | put it away until you're done with it. Once hard disks
             | became standard equipment, the floppy drive was relegated
             | to data transfer and you almost always wanted "Put away",
             | but renaming the menu items to what new users expected
             | would have confused existing users.
        
           | Reason077 wrote:
           | Modern (as in, the last 20 years or so) versions of macOS
           | still have this feature, _except_ when you start dragging an
           | electable volume, the icon changes to an eject symbol to make
           | it clear that you're not actually trashing anything...
        
           | bonton89 wrote:
           | Better than my similar Mac story from the early aughts. I did
           | not frequently use Mac computers but needed to quickly print
           | a document I had burned to CD. For whatever reason, I was in
           | the Mac computer lab which had nothing but what I believe
           | were Power Mac G3s. Inserting when fine, and I knew from
           | using those original black and white Macs in high school that
           | dragging the disk to the trash would eject. When I did so I
           | was rudely informed I lacked permissions to unmount a disk
           | that I had myself just inserted and used.
           | 
           | Fortunately, the lack of an eject button was a farce on this
           | machine. The CD drive was just your garden variety PC drive
           | and if you aren't shy about abusing the facade door Apple
           | placed over top of it you can still get to the eject button.
        
         | flir wrote:
         | 2012 Macbook Pro had a physical CD eject button (it was top-
         | right of the keyboard). Control was probably routed through the
         | OS, so that may not be what you meant, but it was definitely
         | physical.
        
           | dev_tty01 wrote:
           | I saw a sales droid demoing a Mac at Comp USA years ago. That
           | model had the manual eject/inject button underneath the CD
           | tray because in normal use you never needed to push the
           | button. To eject you drag it to the trash on screen. To
           | inject, you just push on the tray a bit and it detects that
           | and pulls it in. The sales droid was talking about how stupid
           | it was to have the button there because it was blocked by the
           | tray, never realizing that he just needed to push on the tray
           | a bit. Ugh.
        
           | Reason077 wrote:
           | Oh yeah, Macs had _that_ eject button for years. Until pretty
           | late in the Intel era, IIRC.
           | 
           | But you could "eject" (unmount) anything with it, disk images
           | etc. It wasn't hardwired to any particular drive.
        
       | tambourine_man wrote:
       | The Performa 630CD was my first Mac and it warmed my heart to see
       | its picture. That feeling went away quickly as I saw it being
       | used as guinea pig for ROM shenanigans. Save that Performa!
        
         | amatecha wrote:
         | well, normally I'd agree, but it doesn't look like there are
         | any irreversible/destructive changes being made? plus this
         | seems like a pretty valuable experiment/project for the retro
         | Mac community.
        
       | JKCalhoun wrote:
       | > I would love to see an example of what these PDS cards looked
       | like, if anyone out there has some inside knowledge they would be
       | willing to share!
       | 
       | The only thing that came to mind were these Newton development
       | boards from about that era. I believe they were more or less
       | Newtons shoved into one of the slots of a Quadra-like machine
       | (perhaps the PDS slot?).
       | 
       | My memory of that era is fuzzy though.
        
       | sneak wrote:
       | What blows my mind is how active the collector community is about
       | these machines. These machines are over 30 years old--they're so
       | old they're not even regularly on eBay anymore.
       | 
       | I still have and cherish my 8600, the very first Bad Motherfucker
       | computer I ever managed to obtain. :)
        
       | koz1000 wrote:
       | I was working on an 8-bit system back in this same time period.
       | We couldn't afford flash devices and the kit required to
       | reprogram them. But we did a similar trick with an extra write
       | pin located near the ROM socket, then used a special
       | daughterboard filled with SRAM that replaced the ROM and also
       | touched the write line. Now we could just use our cheap debugger
       | and blow an image into the address space the ROM used.
       | 
       | Only downside was that you lost the image on power down, so I can
       | see why EEPROM was more important to Apple in developing their
       | systems.
        
       | NelsonMinar wrote:
       | Adjacent: does anyone have a good article describing how Macs
       | used to boot from ROM? Not just some sort of BIOS but the full
       | MacOS System. It seemed like a really neat feature, but IIRC
       | quickly became useless because there was no way to update the ROM
       | so you'd end up loading the OS from disk to get the latest
       | version.
        
         | vanchor3 wrote:
         | There's a brief write-up on porting it to other Macs here:
         | http://www.synack.net/~bbraun/macromboot.html
        
         | retrac wrote:
         | > Not just some sort of BIOS but the full MacOS System.
         | 
         | It's not quite the full system. It may be best to think of the
         | original Mac OS as a software library. The application is in
         | primary control, and uses the OS as a library directly -
         | jumping right into the OS code sometimes. Modern ideas about
         | layers of separation and protection did not yet exist.
         | 
         | A significant portion of the ROM is QuickDraw, routines for
         | doing bitmap graphics and text very quickly. There are some
         | other rather generic routines, like string handling, a sort of
         | a standard library. There are also drivers, interrupt and timer
         | handling, etc. The Chicago system font is in ROM too.
         | 
         | Since it was all designed together, it was not too hard to just
         | make it modular, and have some of the modules in the ROM, and
         | the rest loaded from disk. There is a central dispatch table
         | kept in RAM. When a program makes a Mac OS call, the dispatcher
         | looks up the current vector from the table. When the OS loads,
         | any patches to ROM are handled by redirecting the dispatch to
         | the new routines or patches. It's important to remember classic
         | Mac OS had resources (labelled sections). Large blocks of code
         | are referred to with handles, not pointers. The resource
         | manager can transparently load/unload them behind the scenes as
         | needed.
         | 
         | The Mac has gone through a fair bit of setup before it starts
         | reading the disk. The OS memory manager is running, and the
         | device manager is configured, the disk driver service is set up
         | as well. The boot splash (grey background and the happy Mac
         | icon) is drawn using standard graphics API calls. The calls
         | would do the same thing if used in a normal Mac OS app. The
         | boot sector on disk is loaded using the same calls as in a Mac
         | OS app if you wanted to do low-level disk access.
         | 
         | The resource manager is then told about all the resources in
         | the system file, and any patched resources are patched, etc.
         | And then the finder application is loaded and started. When it
         | goes to look for resources, it'll find them mapped to ROM or
         | the system file through the in-RAM resource map. And when it
         | goes to make a system call, it'll find them mapped to ROM, or
         | the routines loaded in RAM from the System file, through the
         | trap table.
         | 
         | Here's a good article (2019) doing a much deeper dive:
         | https://macgui.com/news/article.php?t=496
         | 
         | > became useless because there was no way to update the ROM
         | 
         | The original Mac 128 and 512 were limited, because their ROMs
         | were the original code, and also 64 KB in size. The later Mac
         | software needed at least 128 KB of ROM (new file system, etc.)
         | and so could never run on those machines. But later system
         | software was never going to run on those machines, anyway.
         | 
         | RAM was extremely expensive in the mid-80s. That is really the
         | only reason for this. The original Mac would have needed an
         | extra 64 or 128 KB of RAM otherwise. That would have bumped the
         | price up several hundred dollars. RAM prices imploded shortly
         | after the Mac's release, of course. System 7 loads around 100
         | KB of patches to the ROM on a Mac Plus. By 1990 it would
         | clearly have been better to just have it all in RAM. But the
         | architecture was already fixed. (Later Macs would just load a
         | complete ROM image off disk.)
         | 
         | There is one more minor factor: the original Mac can execute
         | code from ROM at full speed. The RAM is contended with the
         | video hardware and has slightly slower throughput. So there is
         | a slight plus to having QD in ROM!
        
           | bonaldi wrote:
           | > It's not quite the full system.
           | 
           | You're right about the ROM, but parent is talking about
           | something else: the built-in bootable system that came in ROM
           | on the Classics. Cmd-opt-x-o at startup would boot you
           | straight into 6.0.3, at the cost of RAM (it made a RAM disk
           | to run from).
           | 
           | https://lowendmac.com/1990/mac-classic/
        
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