I have a relatively coherent, if typo-laden, discussion of the different Macintosh generations in the late 90s and early 00s at Choosing Legacy Hardware to Upgrade for Play or Work, What to Get and What to Avoid in which I essentially conclude that, at that time (mid 2005), the PowerMac AGP G4 was the slightly-older-used-machine of choice.

That is likely true in that the G4 AGP machine is about as old as you want to go if you want Mac OS classic support, easier upgradability and at least some compatibility with the modern world, but don’t want the hassle of the truly old Macs. It has PCI slots, native USB support, native ATA support, and DVI video out. This means a world of used PCI cards, modern keyboard and mouse support, including for startup options, caveat-encumbered support for modern hard drives and SSDs, and support for the use of modern monitors with a cheap DVI to HDMI adapter. The PCI slots allow easy addition of USB 2 ports and more modern ATA cards (although you almost certainly need to find those used). These machines are not special nor old enough to be valuable so they are cheap. Unfortunately they are not new enough to be really useful which makes them cheap.

So, if you have one they are a worthy project, and a much easier one than a Mac two generations older, which will require harder to get peripherals such as ADB keyboards, and is much faster and more upgradable then a Mac even one generation older. They also natively support booting into both OS 9 and OS X and support running classic apps in OS X. So it is a good choice to be able to run older classic Mac apps but with at least some of the stability of OS X and the maintainability of a more modern platform.

For the PowerMac G4 AGP the big downsides are:

1. Built in ATA 66 controller does NOT support drives bigger than 128GB and, in solidarity with their older brethren, will reliable corrupt larger drives given time. You can partially work around this by using Intech’s ATA HiCAP drivers, which requires your partitions to be <128GB and your boot partition to the be first one, but will allow you to see the rest of your drive. This is true until the very end of this generation of Macs in around 2003 when they got ATA 100 controllers and can see larger drives.
2. Rage 128 Pro video standard, which does not support higher resolution monitors or Quartz Extreme. Getting a Mac version of a card that does support QE is expensive, and modifying a PC Card is doable but complex. Support for QE can result in significant speedups by shifting much of the basic graphics work of supporting the OS to the video card. The next model came with an option of a better QE compatible video card, and they were standard after that.
3. Version of Safari that is available on the most recent supported version of the Mac OS (OS X 10.4.11) is essentially worthless on the modern internet.
4. Most recent supported version of Mac OS is OS X 10.4.11. Mac OS X 10.4.11 was a massive upgrade from O X 10.3. OS X 10.3 is where Apple essentially finished a long public beta and 10.4 is when the Mac OS began to move forward. It is usable. Mac OS X 10.5 is another huge leap forward and is much closer to our current Mac OS. Mac OS X 10.5 feels modern.

So my recommendation is, you can absolutely make the PMG4 AGP work, and much easier than a PM8500, but if you are wanting an older Mac computer, that is cheap, easy to make work, has support for the modern world such as USB peripherals and larger hard drives and SSDs, has a much better (standard) QE compliant video card, can run classic apps (in OS X 10.4 or natively booted into Mac OS 9.2), and can also run Mac OS X 10.5, then get either a later PowerMac G4 Quicksilver, or one of the PowerMacG4 Mirrored Drive Doors. Those are still computers that are more than 20 years old and are only $200 to $300 as of 1/2026.

1999 PowerMac G4 AGP tips.

Operating system:

You can boot the PMG4 AGP into a later version of OS 8, or any version of OS 9, or OS X 10.0 through 10.4. It can run OS X 10.5, and does so without problems, but that is not a supported install, and doing so requires either hacking the install CD, or just copying a working installation from a newer PPC Mac with a working 10.5 install. Mine has a working 10.5 install, dating from 20+ years ago, but it is a bit pokey on the G4 AGP, and although is has a much never version of Apache (v2.2) and a version of Safari which will at least load pages on the modern internet, it was too slow for me and I am running 10.4.11.

ATA controller:

It has built in ATA 33, which is really meant for optical drives, but can run smaller ATA drives. It has built in ATA 66 for the hard drives but only has 28 bit addressing and cannot see drives larger than 128 GB, which really means it can only see the first 128 GB of any drive, then it corrupts the drive. You can plug a modern SATA drive into the bus using a cheap SATA to ATA adapter (available on Amazon for less than $10 as of 1/2026).

There are several solutions for this hard drive limit:

1. Use drives smaller than 128 GB (any modern smaller SATA SSD will work fine)
2. Use a larger drive divided into 128 GB partitions, keep you boot partition as the first one, and install the Intech’s ATA HiCAP drivers (until Intech yells at me I will mirror them here).
3. Install an ATA 100 or better PCI card. This will allow you to see any size drive you want, and if you get a Mac compatible one, you can boot from it. I have an Sonnet branded ACARD 6280M ATA 133 PCI card and it works great. I currently have a 1 TB SSD and a 2 TB HD, both bootable into both Mac OS 9 and Mac OS X.

Hard drive gotchas.

You cannot (apparently) connect more than one SATA drive to each ATA bus, even though they would support two ATA drives. You cannot connect both an SATA drive and an ATA drive to the same bus. When using SATA: one bus, one drive.

USB:

The built in USB is slow, 1.1 and 12Mbps. You can add a USB 2.0 PCI card that is fast enough to make USB drives (hard drives and USB drives) usable but you cannot boot off them. You can boot from the built in ports…at 12Mpbs.

Video Card:

The older Sawtooth PowerMac G4 came with ATA Rage Pro 16 MB AGP cards, which are too small to see anything larger than a 1024 x 768 monitor, and too primitive to do Quartz Extreme.

Solutions:

1. Don’t waste your money on a monitor that has a resolution larger than 1024 x 768 and just use the included video card.
2. Get an old Mac AGP video card and enjoy larger monitors and QE (expensive)
3. Get an old PC AGP video card (carefully selected), replace the ROM chip with a larger one, flash it Mac, enjoy larger monitors and QE.
   

Note that for a couple of generations after the G4 AGP the PowerMac used non-standard video cards and connectors that carried power for a monitor. Be sure you know what card your system uses before you try to upgrade it, or modify a connector.

I chose door number 1. I am almost certainly going to try door number 3 because…of course I am. When I do that I will l document the process in detail, and link to any equipment or supplies I needed.

Web Browsing:

The OS X 10.4.11 version of Safari (apparently v3.0.4) does not support the modern security architecture that basically the entire modern web demands. The vast majority of sites just flat refuse to load. The ones that do are...slow. The best solution I have found is AquaFox. This is basically a less ancient version of FireFox for old PPC Macs that appears to be being actively worked on and will load sites. Don't get me wrong, this is still a limited option. AquaFox's support of the current web is limited*, and it is very slow compared to a modern web browser on modern hardware.

 

Networking:

The PMG4 AGP came with a built in RJ45 10/100 Ethernet port. Some came with built in Airport (not mine). The best bet for getting online is to use the Ethernet port, either via a WiFi bridge, or directly.

I hope anybody finds this useful.


*I think this is one developer trying to maintain the home fires, which is challenging. I salute him as otherwise we would have no options. Please show your support!