The purpose of Wikipedia is to present facts, not to train. Please help improve this article either by rewriting the how-to content or by moving it to Wikiversity , Wikibooks or Wikivoyage. Referring to the previous example of the MB PowerBook, the following command essentially disables the second RAM stick note that this change is not written to NVRAM - it is transient - once you reboot, the other chip will be detected and used as before: A less adventurous and more appropriate way to limit visible RAM is to use the maxmem boot argument, such as at the shell prompt: The following command sequence shows you various information on the machine's CPU s: The following command expands the alias hd , and gives you the complete path of the device in the tree type devalias by itself to see a list of current aliases, along with what they refer to: For example, if you want your email address to be used as the "OEM banner", you should do the following: Operation When an Open Firmware equipped Macintosh all current Apple systems at the time of this writing is powered on, hardware is diagnosed by some POST code and initialized.
The following "snag" keys let the user specify a boot device as the system is powered on: C device referred to by the 'cd' alias, a CD-ROM drive D device referred to by the 'hd' alias, a hard disk drive N device referred to by the 'enet' alias, a network card Z device referred to by the 'zip' alias, a ZIP drive It is worth noting that pressing T while your Mac powers on would boot it into what's called the FireWire Target Disk Mode.
You can also specify the complete pathname of a device, or have the machine boot over the network using TFTP: The sequence of events when BootX starts executing after being handed control by Open Firmware is described below: BootX first initializes the Open Firmware client interface that it would use to talk to the firmware , and retrieves the firmware version. BootX looks up the options device in the firmware, which contains various variables that you can see and set using the printenv and setenv commands in Open Firmware.
For example, the following command at the Open Firmware prompt shows you the contents of chosen: BootX initializes handles to the MMU and memory using chosen.
BootX initializes handles to the boot display and the keyboard if present. BootX checks if the "security mode" is "none", or BootX checks if the "verbose" cmd-v or "single user" cmd-s flags were specified, and sets the "output level" accordingly. BootX checks if the system is booting in "Safe Mode". BootX claims memory for various purposes. BootX finds all displays and sets them up.
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It does this by searching for nodes of type "display" in the device tree. The primary display is referred to by the screen alias. For example, you can try this at the Open Firmware prompt: While opening the display s , BootX also sets the screen color to the familiar whitish gray.
BootX looks up the boot device, boot arguments, etc. At this point, BootX draws the Apple logo splash screen, and starts the spinning cursor. If booting from a network device, a spinning globe is drawn instead. Depending on various conditions, BootX tries to retrieve and load the kernel cache file.
The next step is to "decode" the kernel.
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If the kernel header indicates a compressed kernel, BootX tries to decompress it typical LZSS compression is used, as you compress this kind of data once but expand it many times. Since the kernel binary can potentially be a "fat" binary code for multiple architectures residing in the same binary , BootX checks if it indeed is fat , and if so, "thins" it figures out the PowerPC code.
BootX attempts to decode the file possibly "thinned" as a Mach-O binary. If the above fails, BootX gives up, draws the failed boot picture, and goes into an infinite loop. If BootX is successful so far, it saves filesystem cache hits, misses and evicts, sets up various boot arguments and values such as whether this is a graphical or verbose boot, whether there are some flags to be passed to the kernel, the size of installed RAM , and also calls a recursive function to flatten the device tree.
Finally, BootX "calls" the kernel, immediately before which it "quiesces" Open Firmware, an operation as a result of which any asynchronous tasks in the firmware, timers, or DMA get stopped, etc.
BootCache Mac OS X uses a boot-time optimization effectively a smart readahead called "BootCache" that monitors the pattern of incoming read requests to a block device the boot disk , and sorts the pattern into a "playlist" it also measures the cache hit rate and stores the request pattern into a "history list" for being adaptive in future.
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The boot. The Boot: partition only contains a few Open Firmware related files and isn't used for anything else than to get the kernel loaded by the machine itself. When booting manually from OF, you'll see some output lines on screen. There are two important lines that tell you the boot stage. This can be demonstrated well with the load and go commands. Problems after that stage are MorphOS related, and if the MorphOS boot image doesn't appear soon, then MorphOS might not have found a device or image to boot from, or there might be driver or compatibility issues.
MorphOS reset keys Ctrl-Lcmd-Rcmd, Fn-alt-alt also work at this stage even if there are any other problems halting the boot process. A shorter, and usual, way to boot is to use the boot command, which combines both load and go commands. Several boot arguments can be given to the boot. Without arguments MorphOS boots a device that is bootable and has the highest boot priority set.
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Note that this only applies to partitions that contain a MorphOS compatible bootable filesystem. The HDConfig tool can be used to set partitions bootable and alter their boot priorities, but usually it's unnecessary to change these settings. The arguments can be given in a longer or shorter, in parenthesis format. MorphOS documentation's usual advice is to boot the machine with the c key pressed, but that method can sometimes be unreliable for one reason or another, so you might end up in a situation where a boot image has been loaded from a HD and the actual system from a CD, which results in an error if the boot image and the CD aren't from the same MorphOS version.
A more reliable way is to boot into the Startup Manager menu on Macs by holding the alt option key at boot, and select the CD from that graphical boot menu. Pressing the F12 key in the menu will eject the CD. As well as the previously mentioned methods, there are other ways to boot a CD from the Open Firmware prompt. As you can see, there are several different boot images for different architectures.
The blessed directory is marked with an asterisk. The system would most likely boot from the CD even without this argument, because of the previously mentioned boot priorities. If you can't access your FAT formatted USB stick, refer to the official guide on how to re-format it in a compatible way. Some Macs can be more picky about the format than others, and the same stick, that works in G4 Macs, might not work in a G5 Mac, etc.
If you still have issues with USB stick detection in OF or can't format the stick properly, this section of the tutorial provides some alternative methods to get a system booted. The following examples assume that you have a correct boot image file named as boot. The files may be named differently too, there's no problem if you want to keep different versions around and boot whichever you want.
You could have boot So, the basic idea is to boot the system from an ISO image without burning it or extracting files from it.
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This can be achieved by giving the ISO image location to the boot image with the bootimage argument. Some firmware versions create a ud alias, which points to a USB mass storage device connected to the computer. List the aliases to find out if it's been created. If that doesn't work, try to list the contents of the USB stick to find out if it's in a compatible format:.