Linux on the Low End

Preparing Your PCI Power Mac for Linux

- 2006.07.26

Last week I introduced myself and spoke of how I would try to help others get Linux running on their low-end Macs. This week we'll look at what hardware is needed and which hardware will make for a faster running system. Keep in mind that some of this may appear to be intimidating, but doing your homework now will hopefully avert problems later on.

Minimum Recommended Hardware

I recommended certain types of Macs last week, and I will expand upon that now. I don't recommend installing on Linux NuBus Macs mainly due to lack of support - some things work and some just don't. I intend to focus on the Old World PCI-based Macs, which are well supported but need more preparation to get Linux up and running properly than the New World machines.

Processor: 603s and 604s are adequate, but a G3 or G4 will give much better performance due to the faster, larger, integrated backside Level 2 (L2) cache. Faster isn't always better - having more memory will give you a more noticeable speedup than a faster processor with too little RAM. Running a G4/800 with 64 MB RAM will be no faster than a G3/400 with 512 MB RAM, if not slower.

Linux programs can make use of the AltiVec "velocity engine" of the G4, but it's not a necessity. Further, I have seen some issues with getting the G4's L2 cache working correctly on Old World machines. Good speed G3s can be found on eBay for around $25-100 depending on your machine. G4s usually carry a hefty premium that doesn't always show the best return.

Memory: 128 MB is a good start; 256 MB or more is better. I have installed a modern Linux with just 80 MB RAM on a Power Mac 7500, but it was really slow.

512 MB would be excellent, and I don't really recommend any more than that. With 256 MB RAM, I still have over half of that free or being used by Linux as disk cache, so unless you're running OpenOffice and the GIMP at the same time, you don't need to go crazy.

Also keep in mind that the 4-digit Macs used Fast Page Mode (FPM) memory. Some also accept EDO (Extended Data Out) memory and use it like FPM. FPM memory has different notches than the newer SDRAM used since the Beige G3s, and they won't interchange. Most PCI machines support interleaving memory (using slot A1 and the B1 instead of A1 and A2), which can give about a 20% speed boost.

Hard Drive: The stock MESH (Macintosh Enhanced SCSI Hardware) controller on the Old World Macs is abysmally slow. It's only a 5 MB/s controller. The NCR controller was slightly better, at 10 MB/s, but most of the Macs I have come across have the drives connected to the slower MESH controller.

The onboard controllers are fully supported, but I recommend a PCI SCSI card. Adaptec's 2940 series are very fast (up to 80 MB/s), show a large improvement in speed over the stock cards, and are available on eBay for around $10.

A PCI IDE controller can be a good choice as well, and all the newer IDE drives are much faster than the old SCSI drives anyway. Further, the CD-ROM drive can be connected to the NCR or MESH controller to allow the hard drive to run at full speed on the faster controller.

The newest option is PCI SATA controllers, which should work without a hitch on PCI Power Macs, clones, and beige G3s. More on that after some testing.

Video Card: Linux supports ATI Mach64 based cards, like the Rage IIs, the Rage LTs, etc. They will work fine, and some Macs have these onboard, like the Beige G3 and the WallStreet PowerBooks. For those who can get one, a Rage 128 or a Radeon 7000 would be a better choice on the higher end, and are also available on eBay for around $10-30.

Some Macs came with the ixMicro Twin Turbo card (such as the Power Mac 9600). While this is a decent video card, there is very little support for it. I have managed to get them to run under X-Windows, but not well, and when I tried to adjust the settings, I lost the ability to run X-Windows. For this reason, I don't recommend it.

Other PCI Macs, like the 7500, have an onboard frame buffer device that will work under Linux and X-Windows, but it won't be very fast. A low-end ATI video card will be faster. Further, you can do a dual head display under X-Windows using the onboard video along with a PCI video card.

Note about ATI under Linux: There is a bug in the Linux driver for the ATI cards under text mode that causes there to be several vertical lines that are fuzzy and hard to read. This bug does not affect using the GUI under X-Windows, only text-mode.

Preparation: This is the key to a smooth install. Inventory what your system has and what it may need, as well as what you can do to make it better. A useful tool is the Apple System Profiler (under the Apple menu). This will give you lots of info about your Mac. Newer versions of the Mac OS will show more information, but you should be able to get what you need from any version newer than 7.x.

Under the System Profile tab:

  • Memory overview: Shows built-in memory and L2 cache, if available. Ignore the Virtual memory info. (Linux handles virtual memory differently from Mac OS and WinDoZe)
  • Processor info: Listed under Hardware Overview in v9.2.2. This shows your processor type and machine speed.

Devices and Volumes tab:

Under this tab, you will find info on your hard drives, video cards, CD/DVD drives, etc. You will have to click on the arrows to expand the fields to get all the info. If you have a non-Open Firmware PCI card installed, it will not give much information on it, but don't worry, Linux will be able to make use of it. The only PCI card that I never got working on a Mac under Linux was a Via-based USB card.

Summary

  • Processor: 603 or 604s are good. G3s are great. G4s work, but may require extra steps to get the L2 backside cache to work properly (I will delve into this more when I can).
  • Memory: 128 MB to 256 MB RAM. No more than 512 MB really needed.
  • Video: ATI Rage series. ATI Rage 128 or Radeon recommended. ixMicro not recommended. Onboard video works, but can be slow. Primary display has to have an Open Firmware BIOS.
  • Hard Drive and Controller: PCI-based SCSI or IDE controller connected to a newer drive will give best results. Otherwise, connect the hard drive to the NCR controller and the CD-ROM to the MESH controller. The PCI card does not have to have an Open Firmware BIOS. I recommend that Linux be installed on a drive separate from Mac OS if at all possible to make this as easy as possible.
  • OS X and the 8 GB limit: Those of you you have installed OS X on a low-end Mac have probably run into the 8 GB limit. Linux does not have this problem and will successfully install onto any size drive. Further, I have successfully installed Linux on a Beige G3 with a Rev A ROM on a slave drive with no problems. OS X requires a Rev B or C ROM to be able to see the slave drives.

Hopefully I haven't scared you away with all this "geek" speak. It's probably more than what some Mac users may have ever dealt with, but having all this info ready will make the install that much easier. Of course, some of you guys may know more about this than I do.... Next time I will discuss how to acquire the BootX Linux boot program and how to set up your hard drives for Linux, and to get ready to start the installation. LEM

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