OSX Fresh Reinstall

Discussion in 'macOS' started by echosystm, Jul 28, 2010.

  1. echosystm macrumors newbie

    Apr 3, 2010
    Hi guys

    I'm new to Macs and I'm still learning how they actually work. I'm a bit anal retentive when it comes to my computers and I like to completely reset them to a blank state whenever they need a reinstall. On a PC, I will typically reset the BIOS and erase the MBR. I would like to know how to do the equivalent on a Mac. However, it would seem very few Mac users have any idea what is really going on inside their computer, so my research efforts have been pretty fruitless. FYI, I am aware that disk utility has an erase option, but this doesn't do what I want it to.

    From what I gather, resetting the PRAM and SMC are somewhat equivalent to resetting the BIOS on a PC. Are there any other things that can be reset, or is it just these two?

    In terms of erasing the "MBR", I really have no idea how GPT works. So far I've just been doing a dd on the first 500mb of the drive (dd if=/dev/zero of=/dev/disk0 bs=512 count=1000000), under the assumption that the GUID data is at the very start of the drive. I know the EFI partition is within the first ~200mb of the drive, so at least that is getting erased. I'm concerned that perhaps the GUID data sits at the end of the drive. Can anyone confirm the location of the GPT on a Mac?

  2. MacDawg macrumors Core


    Mar 20, 2004
    "Between the Hedges"
    Sorry, I can't help you...

    I am just glad I don't have to worry about all of that stuff on my Mac :)
  3. MisterMe macrumors G4


    Jul 17, 2002
    No, it is not. The Mac does not have a BIOS. A BIOS is a 1981 solution to a 1981 problem. It is not 1981 anymore. The closest thing on the Mac to the BIOS is Intel's EFI. However, it is much more sophisticated than a BIOS.

    My suggestion to you is chill on "learning how the Mac works." First, learn how to use it. This will help you to get into the culture of the Mac. It will also help disabuse you of the notion that you have to fix your Mac despite the fact that it is not broken.
  4. larkost macrumors 6502a

    Oct 13, 2007
    You are correct in the generalization that zapping PRAM (not actually PRAM any more, but that is getting into details) is about the closest you can get to resetting BIOS, but once you get past the 10,000 foot-overview stage the differences become huge. If you are not having active problems, then resetting PRAM is only really going to mess with your clock and the system volume. The rest is layers you have nothing to do with.

    Now, onto MBR: here is where Apple has managed to avoid a huge pit that PC makers seem intent on piling into. The PC boot system is ridiculously archaic. I have been working it out in a project for work and it has barely changed in 20 years, and this is not a case where it didn't change because it didn't need to.

    The point here is that there is no boot code in anything like an MBR, unless you are booting Windows on a Mac. Apple uses GPT format by default on all Intel Macs, and that allows for a much more dynamic boot system. The computer actually figures out what volumes are bootable as part of the boot process (PCs do not, it has to be pre-recorded in multiple files). But the nice thing is that the system is so reliable that you don't have to worry about this, just sit back and enjoy doing what you bought the computer for.

    Oddly I am planning on giving a short session at the MacTech conference on exactly this topic.
  5. echosystm thread starter macrumors newbie

    Apr 3, 2010
    When I was talking about the MBR, I was mainly referring to the partition table. Essentially I want to know how to make the hard drive inside my Mac look completely empty to the computer. On a PC, erasing the whole MBR obviously achieves this without needing to write zeros to the entire drive.

    How can I achieve this on a Mac?

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