What is the purpose of amd64+mac images?

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> Beginning with Ubuntu 11.04 (Natty Narwhal), two "new" images are available from cdimage.ubuntu.com:

Correction: beginning with Ubuntu 10.10 (Maverick Meerkat), although in that case they were a bit excessively hidden:

  http://cdimage.ubuntu.com/ports/releases/maverick/release/

> • 64-bit Mac (AMD64) desktop CD
> • 64-bit Mac (AMD64) alternate install CD
>
> Both are described "This image is adjusted to work properly on Mac systems." What _exactly_ is the difference between these and the standard amd64 images?

In 10.10, I changed the standard amd64 images to dual-boot on either BIOS or UEFI systems (UEFI, "Unified Extensible Firmware Interface", is a different kind of firmware found on many newer systems). This was done using a technique known as a "multi-catalog" CD - it contains two boot images, and the specification says that the firmware is supposed to pick the one it can best use.

Unfortunately, even though Macs use a variant of EFI (an earlier version of what's now called UEFI), they apparently can't cope with multi-catalog CDs, and simply refuse to boot them (https://bugs.launchpad.net/bugs/633983). This left us in rather a quandary: we needed to support UEFI systems, but we didn't want to drop support for Macs either. I therefore created the amd64+mac CD images, which are exactly the same as the amd64 images except that they only support BIOS booting. Macs are happy to boot these in their BIOS emulation mode.

(In fact, the name amd64+mac is a slight misnomer, because it later turned out that some systems other than Macs suffer from a similar problem - but I felt that a more technically accurate naming such as amd64+nouefi would be more likely to confuse than enlighten.)

> Do they contain everything one needs, or do users still need to reference the mactel-support PPA?

The difference described above is the *only* difference between the amd64 and amd64+mac images. Any requirement for the mactel-support PPA (and honestly I have no idea what's in there) has not changed.

> Why are there no "32-bit Mac" images?

There's no need for them, because the i386 images still only support BIOS booting, and so the conflict with the Mac firmware doesn't arise. This is partly because very few people care about booting a 32-bit operating system on UEFI - and the UEFI people tell me that it's dubious whether that's even consistently supported - and partly to avoid this very problem.

> Which Mac models require the use of these discs?

I have no idea. I don't actually have suitable test systems myself; I was responding to bug 633983 as mentioned above.

> Does the 64-bit PC (AMD64) install/live DVD contain the Mac support bits, or are they only available on the [separate] CDs?

The "Mac support" is in fact an *absence* of UEFI support.

> If someone goes to http://www.ubuntu.com/download/ubuntu/download to download a Desktop image, why are the only choices "32-bit (recommended)" and "64-bit?" Why is "64-bit for Mac" not an option here?

No idea; you'd have to ask the website people. I guess it's hard to present gracefully or something. Also we don't have room for the amd64+mac images on releases.ubuntu.com, which doesn't help.

> Why are the amd64+mac images not mentioned on https://help.ubuntu.com/community/GettingUbuntu ?
>
> ... on https://help.ubuntu.com/community/GraphicalInstall ?
>
> ... on https://help.ubuntu.com/community/MactelSupportTeam/AppleIntelInstallation ?
>
> If someone goes to the Apple Users Ubuntu Forum — http://ubuntuforums.org/forumdisplay.php?f=328 — why isn't there a Sticky Thread explaining this?

There is no practical way for me to keep up with all these different places people decide to document things. Please do feel free to update these various different places. I'm an installer and CD build developer, not specifically an expert in running Ubuntu on Macs.

> If I want to try Ubuntu under Parallels, VirtualBox, or VMware Fusion, do I need/should I use a "Mac" image, or a standard one?

I believe the standard image should work fine.

> amd64+mac images also appear in the Oneiric Daily Builds. Why haven't the Mac "adjustments" been merged into the standard amd64 images?

Because that would break support for compliant UEFI systems, which are important as well. We're caught between the fire and the frying-pan here.

While I would love to return to shipping just amd64 images rather than both amd64 and amd64+mac, at the moment there is no prospect of reunifying them unless somebody figures out how to make a multi-catalog CD image that Macs can boot. If you're an expert on Mac firmware, this would be a great thing to work on.

Need to un-expire this

I think my answer above (#2) should address this.