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The Amiga computers were advanced machines meant to do all sorts of things, including file management. They had a GUI OS (Workbench) and everything right from the very start. They were not some games-only console such as the NES or SNES.

In spite of this, it lacked a battery inside of it which could have enabled it to keep the date/time when it was powered off.

If you powered on your Amiga 1200, set the date and time, then saved your file to the hard disk or a floppy disk, and then turned it off, it would have forgotten the date and time the next time it was powered on.

Only if you bought one of those "accelerator cards" that you put inside the hatch underneath the Amiga did you (typically) get such a battery as a "bonus" and were then able to actually turn off your computer.

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    To the close voter, why vote to close? This question is direct and answerable - either a primary source connected to Commodore replies, or a secondary source like a magazine or forum with an interview with someone where the subject is raised is found.
    – knol
    Feb 10 at 23:22
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    How likely do you think it is we're going to find a Commodore quote discussing this @knol? We already have one answer, and, however interesting, it's, essentially, opinion. Feb 10 at 23:55
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    @WillHartung There are lots of Commodore interviews with engineers and management, and books and presentations written on the subject of the Amiga. It's a popular series of computers, created by passionate engineers. So I would say 'highly likely'.
    – knol
    Feb 10 at 23:57
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    The Raspberry Pi has no RTC either.
    – AndreKR
    Feb 11 at 15:49
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    For retrocomparison,, PDP-11 minicomputers (at least,, the TTL systems; I didn't deal with later models) did not have a 'clock' in the sense that a battery would be any use. While the system was running, the OS tracks time by counting intterupts, either line frequency or a programmable timer. Feb 11 at 17:48

5 Answers 5

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You specifically mention the Amiga 1200 in your question, but your statement about real-time clocks is not true for Amigas, in general.

From 1987, the Amiga was offered in at least two versions aimed at two different markets. Beginning with the A500 and A2000, the A500 was meant as a relatively low-cost "home" computer, whereas the A2000 was aimed at "professional" and "prosumer" markets and cost about double. The A2000 included a real-time clock with battery backup. For the A500, this was an option, and was part of the "belly slot" memory expansion that increased RAM to 1MiB. It is noteworthy that most A500 users bought this expansion option too, but mainly for the added RAM.

Definitely, it's reasonable to question why was this an optional add-on for the A500. And the answer is almost certainly that Commodore shaved cost from the A500 wherever possible, because that was the intention with their low-end machines.

The A3000 (successor to the A2000) also included a real-time clock and battery. As did the A4000.

The situation with the later A1200 was not much different than the A500. The "belly slot" was changed to accept more sophisticated expansion devices than the typical RAM+RTC, and so the "Clockport" interface was added so that A1200 users could still easily add an RTC for nominal cost, if they wanted it.

I'd say Commodore's marketing and profit intentions were the driver here. Also, it's consistent with other low-end home computer manufacturers of the time. It was frequently the case that competitors to Commodore also made the battery-backed RTC an add-on option.

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    I'll just add that the slightly more up-model A500+ that came with 1MB of memory onboard also included a RTC and battery on the motherboard.
    – mnem
    Feb 11 at 0:27
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    And if you own an A500+ you should make it a priority to inspect the board and ensure said battery hasn't leaked!
    – knol
    Feb 11 at 0:30
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    Also worth noting here is that an RTC and battery is included on the A1200 motherboard and schematics, just not populated with circuits.
    – pipe
    Feb 11 at 8:11
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    So it all boils down to: If an Amiga has an RTC, it also has a battery. :-D Feb 11 at 10:55
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    Nitpick: the "belly slot" of an A500 could accept more than just RAM+RTC. Mine has for example a KCS PC emulator board in it.
    – Edders
    Feb 11 at 12:07
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Why did the stock Amigas not have a battery for keeping the time/date?

It might be worth noting that neither the original A1000 nor the home computer Amigas (500/1200) had a clock at all. Time was kept by software alone, thus only present while running. Adding a battery wouldn't have changed this at all.

A real clock device was an extra to be added (*1).

In this it was not different from other computers of the time, even more expensive ones, like the IBM PC and PC XT.

If you powered on your Amiga 1200, set the date and time, [...], and then turned it off, it would have forgotten the date and time the next time it was powered on.

Not really, as AmigaDOS quite cleverly used the last modified date (*2) from its boot volume as default for the clock value. That way it was guaranteed that time/date stamps of consecutive sessions were increasing - which is a very useful feature to reconstruct the sequence of save files when needed.

It was a common trick to write some meaningless file when shutting down the computer - that is, if one was too strapped to buy an RTC.

Only if you bought one of those "accelerator cards" [...] did you (typically) get such a battery as a "bonus"

The important part wasn't the battery, but a clock chip, able to keep and progress time when the main computer was powered off.


*1 - Not as easy for the A1000, as various really odd designs, like the mouse-clock, show.

*2 - Amiga DOS writes a last-modified time stamp onto a volume whenever a file on the volume gets modified.

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    Good point on the lack of a RTC. When I read the question, because lack of time-keeping capability is "always" no clock rather than no battery, I completely missed that the question was focused entirely on the battery. Feb 11 at 13:13
  • A further requirement for a battery-powered clock is that the clock hardware draw minimal current when the rest of the CPU was powered down. Although it would have been cheap and easy to include hardware in one of the custom chips to maintain time/date without any CPU intervention whatsoever, extra processing steps would likely have been required to allow that part of the chip to use a separate power rail from the rest of the device, and keeping the whole chip powered off a battery would have resulted in absurdly short battery life.
    – supercat
    Feb 11 at 18:11
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    Fun fact: That same ‘trick’ of using a file timestamp written during shutdown is actually still used in a number of places today for systems that lack an RTC, such as the Raspberry Pi, though it’s usually done with a specific ‘well known’ file path these days instead of embedding a timestamp into the filesystem metadata. Feb 12 at 0:58
  • @AustinHemmelgarn Of course. I never wanted to imply it was unique to the Amiga. It has been used before (and after) many times. The advantage of AmigaDOS was that it was prepared to do so. so no need to use an aftermarket hack, like a well known path.
    – Raffzahn
    Feb 12 at 1:33
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Modern PCs have a separate chip to generate the real-time information. This is in a special low-leakage technology to maximise battery life. The typical 1980s PC used a counter timer which would have been part of the main chip, and as such could not be made economic to power from a battery due to its high power consumption. Since these devices were made with very thin cost margins, it would not be worthwhile to offer a separate clock chip as standard.

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The real answer is that 2 of the engineers named on the original Amiga OCS patents had just completed the design and development of a semicustom CMOS real-time clock chip (2nd source?) for the original Apple Macintosh (latter renamed 128k). And didn't want there to appear to be any conflicts of interest with that almost contemporaneous IC design project.

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Because Commodore was very, very very cheap. Why include something that you could get the buyer to pay more for?

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  • The IBM PC didn't have an RTC, and it wasn't cheap. Neither did the Apple IIc, the BBC Micro, the Atari 130XE, the Amstrad CPC6128... Seems like a lot of contemporary computer manufacturers were 'very very cheap'. And a good thing too. So many expensive computers have been destroyed by leaky RTC batteries. Feb 15 at 9:22
  • @BruceAbbott: I wonder why more devices didn't use battery holders that were designed to contain any battery leakage?
    – supercat
    Feb 15 at 19:01
  • @supercat some did eg. Amstrad, Apple - but for primary cells not rechargeable. But standard dry cells had short lifen and high capacity lithium batteries were very expensive. NiMH had the advantage of 'never' needing replacement, and in the days when PCs were turned fully off when not in use the battery drained faster than they do today. I think the problem is that PC manufacturers believed the data supplied by battery manufacturers, which said they could be charged indefinitely and wouldn't leak! Feb 15 at 22:11
  • @BruceAbbott: I wonder if it would be possible to design a device which would fit around an alkaline AA or AAA cell (different device for each) but would have a bulge which could accommodate leaking battery ooze. Or perhaps have a device fit around an AAA sell but have exterior dimensions sized for an AA (again with space to hold ooze).
    – supercat
    Feb 16 at 0:16

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