- Are You Still Working So Late Mac Os Catalina
- Are You Still Working So Late Mac Os Sierra
- Are You Still Working So Late Mac Os Download
Mac mini (Late 2012 to late-2018) iMac (Late 2012 to mid-2017) iMac Pro (all models) Mac Pro (Late 2013, plus mid-2010 and mid-2012 models with recommended Metal-capable GPU) High Sierra compatibility. If you are running an earlier version of OS X, you can still give it a try. In the sidebar select your OS X disk click the First Aid tab click Repair Disk If Disk Utilities does not work, then I. Clean up your Mac from system junk. As a general rule, a fresh macOS requires a fresh hard drive. There are tons of outdated caches, app leftovers, plugins, and system logs on any given Mac. Not only do they take a lot of space, but they may also be causing various kernel-level errors. You can still install the OS. The trick is back dating the systems clock! Alter the Date & Time setting from auto set to manual and then alter the date to a year that is within the given OS’s release window. Now your older OS installer thumb drives will work! Why Mac users still use OS X Snow Leopard. Upgrading software or equipment until there's a pressing need to do so. The build quality and long working life you get when you buy a Mac.
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Is your mac starts getting slow after updating to macos Catalina os x ? or the performance of your MacBook Pro or air has been low now. In this guide will tell you how to fix slow Catalina os x performance.
Before anything else, one thing to suspect is that your physical Mac laptop or desktop doesn’t actually support this latest edition of macOS. This could certainly be the case if your Mac was made before the year of 2012 as it won’t be compatible with macOS 10.15 Catalina. If you find yourself finding that this was the reason why the only solution you’ve got really is to disable some of the new features that came along with Catalina to see if that starts to speed up the computer. However if this reason doesn’t apply to you and your Mac does indeed support Catalina, all is not lost. There are plenty more things we’re going to be able to try to try and speed up your Mac OS system. Throughout this tutorial, we’re going to be looking at first and foremost the reasons why your macOS Catalina slow, and secondly what you can do to fix these issues.
How to speed up macOS Catalina
It is actually to be expected for your Mac to be running slow should you have just gone through the process of installing macOS 10.15 Catalina. This might be expected; however, there isn’t one single reason why this should be expected. Instead, there are many reasons and solutions that you can try to try and speed your slow macOS Catalina and get it running back to speeds you expect an updated Mac OS Catalina too.
1. Disabling Your Start-up items
When you’re switching your Mac on from it being turned off if you find that it takes forever and a day to boot up this can sometimes cause frustration and stress that you could really have done without. However, all is not lost, there is a solution to speed up the boot process of your Mac OS. Before finding what solution will fix the problem first, you’ll need to find the reason why macOS Catalina slow login. For your benefit, we are going to look at every problem and solution individually so that you know which will work for you.
Try disabling programs that automatically run:
When you first boot up your Mac, there are a series of programs that will just start up themselves automatically without you even noticing. These ‘start-up’ items will always start themselves upon the Mac being switched on unless you tell them to otherwise. The reason that this could be the culprit is that they’re all starting up at the same time upon the machine being switched on and this congestion causing the system to slow down. If you want to stop these programs automatically starting up to follow these steps:
When you first boot up your Mac, there are a series of programs that will just start up themselves automatically without you even noticing. These ‘start-up’ items will always start themselves upon the Mac being switched on unless you tell them to otherwise. The reason that this could be the culprit is that they’re all starting up at the same time upon the machine being switched on and this congestion causing the system to slow down. If you want to stop these programs automatically starting up to follow these steps:
Disable Startup Items on Catalina
1. Click on the Apple Menu in the top left of your screen.
2. Navigate to ‘System Preferences’.
3. From here select ‘Users and Groups’.
4. Now you’re going to want to click your username that should show up on the right-hand side of the screen. After you’ve clicked that, go to the left and click ‘login items’. Now once you’ve done this, it will show you the list of programs that automatically start up when you switch your machine on.
5. Tick the boxes of the programs that you don’t want to automatically, once you’ve made all of your selections click the minus (-) that should be located at the bottom of your window.
2. Navigate to ‘System Preferences’.
3. From here select ‘Users and Groups’.
4. Now you’re going to want to click your username that should show up on the right-hand side of the screen. After you’ve clicked that, go to the left and click ‘login items’. Now once you’ve done this, it will show you the list of programs that automatically start up when you switch your machine on.
5. Tick the boxes of the programs that you don’t want to automatically, once you’ve made all of your selections click the minus (-) that should be located at the bottom of your window.
Fix MacBook Overheating macOS Catalina after Update: Pro/Air
Try disabling start-up items that are hidden
Not all of the programs that start up automatically upon boot are visible. Some of these start-up programs are what we call “hidden”, and for this reason, you might not have already disabled them, and thus they will still be having an impact on the speed of your Macs boot. To resolve this issue, we need to use the Optimization feature that is located in the program called Clean My Mac. Navigate to the program and then follow these steps:
Not all of the programs that start up automatically upon boot are visible. Some of these start-up programs are what we call “hidden”, and for this reason, you might not have already disabled them, and thus they will still be having an impact on the speed of your Macs boot. To resolve this issue, we need to use the Optimization feature that is located in the program called Clean My Mac. Navigate to the program and then follow these steps:
Disabling Hidden Startup items
1. Navigate to the speed tab and select this.
2. Next, find optimization, select it and then click “Launch Agents”. From here you will now see a list of service applications that run automatically when your Mac boots up. What you’re going to want to do now is disable every single one of these applications of alternatively remove them.
2. Next, find optimization, select it and then click “Launch Agents”. From here you will now see a list of service applications that run automatically when your Mac boots up. What you’re going to want to do now is disable every single one of these applications of alternatively remove them.
Now that you have taken care of both the visible and hidden start-up items you might now notice an improvement in the speed that your Mac boots up should you have just upgraded to Catalina.
How to recover dashboard data in Catalina os Mac?
2. Resetting Both Your SMC and NVRAM/PRAM
If either your SMC or PRAM finds themselves in a state of corruption, this can have a devastating effect on the speed of your Mac boot up process. However, there is a way around this corruption, and that is to reset both of them.
Firstly let’s explain what SMC is. The System Management Controller is responsible for the smooth running of hardware such as fans inside your Mac computer. So you need to be careful to follow these steps carefully to reset this. And which set of steps you follow depends on what type of Mac you’re using:
To Reset your SMC on either a MacBook Air, MacBook Pro or a Macbook:
1. Firstly switch your Mac off altogether and remove the power cable.
2. Wait roughly around 15 seconds before plugging your power cable back in.
3. Without first switching on the Mac, hold the Left Shift, Option, Control and Power buttons all together at the same time for a minimum of 10 seconds.
4. Release all the keys and power on your Mac as usual.
1. Firstly switch your Mac off altogether and remove the power cable.
2. Wait roughly around 15 seconds before plugging your power cable back in.
3. Without first switching on the Mac, hold the Left Shift, Option, Control and Power buttons all together at the same time for a minimum of 10 seconds.
4. Release all the keys and power on your Mac as usual.
If you need to reset the SMC on your iMac, Mac Pro, Xserve or Mac Mini:
1. First, you’re going to want to, in the same way as the previous, switch your Mac off and then unplug the power cable.
2. Leave the power cable out for 15 seconds before plugging it back in.
3. Wait a further 5 seconds and switch the Mac back on.
1. First, you’re going to want to, in the same way as the previous, switch your Mac off and then unplug the power cable.
2. Leave the power cable out for 15 seconds before plugging it back in.
3. Wait a further 5 seconds and switch the Mac back on.
Reset your NVRAM or PRAM
You should only be needed to reset your NVRAM or PRAM if there is either an issue with the resolution of your Mac if it is reporting the battery as being at the wrong level or finally if you’re going to boot the Mac up and it’s going from the wrong disk. To reset follow these steps:
1. Switch your Mac off and leave it off for a few seconds roughly.
2. Switch your Mac back on and press the Option, Command, P & R Keys on your keyboard at the same time.
3. Keep these keys held down until you see your Mac restarting while making a beeping sound at the same time.
You should only be needed to reset your NVRAM or PRAM if there is either an issue with the resolution of your Mac if it is reporting the battery as being at the wrong level or finally if you’re going to boot the Mac up and it’s going from the wrong disk. To reset follow these steps:
1. Switch your Mac off and leave it off for a few seconds roughly.
2. Switch your Mac back on and press the Option, Command, P & R Keys on your keyboard at the same time.
3. Keep these keys held down until you see your Mac restarting while making a beeping sound at the same time.
Don’t worry, resetting your NVRAM/PRAM will not cause you to lose any data at all.
3. Try Optimising your Storage
Optimize Storage with Catalina
This is an essential feature on a Mac that organises all of your files and ensures that your storage usage at all times is optimised and nothing is being wasted. It also helps free up and storage space so that you have more disk space is available for you to use. If you haven’t activated this feature you can do so by:
1. Go to the Apple Menu in the top left of your screen.
2. Click on ‘About This Mac’ and then to ‘Storage’ and finally ‘Manage’.
3. You should now see a pop-up message that gives you various options, select the option that says ‘optimise storage’.
2. Click on ‘About This Mac’ and then to ‘Storage’ and finally ‘Manage’.
3. You should now see a pop-up message that gives you various options, select the option that says ‘optimise storage’.
Once this is now activated, the feature will by itself start organising your files efficiently into various categories and will remove any unused files from the system, therefore, clearing up space on your Mac. The reason that this will speed up your Mac is that the Catalina OS now has more space to work with and rely on for its operations so you should see a considerable improvement.
4. Clean up both Your System and App Junk
Another of the main reasons as to why your Catalina Slow could be that you have an abundance of junk files from your system in your current OS before updating to macOS 10.15 Catalina. This will have a domino effect and will start to slow your Mac down after you have updated your Mac.
It could also be that if you have recently installed a new app on your macOS 10.15 Catalina, this could be slowing down your OS. If there is a problem with your App Junk on your macOS and you don’t remove this app junk completely, this will then cause a conflict between both the old app junk and the new app junk.
Clean up both your System and App Junk
If you find yourself needing to delete this app junk, you will have to use the services of a 3rd Party Application. An excellent app to use is called Clean My Mac, which will comprehensively remove all of the app junk from every area of your disk. However, you can choose between deleting everything or only selected areas of the disk. The best feature of this app is that it is intelligent in how it goes about the cleaning process, i.e. it will only clean up what is unneeded and won’t compromise your data or your Macs performance. Once you have removed these files, you should see an improvement in terms of the speed of your Mac.
5. Disable Apps that are Power Hungry using the Activity Monitor
If you’ve got to this stage and still not found the reason as to why your Mac is running slow after the Catalina update whilst at the same time noticing that the fans are spinning a lot faster than usual, then don’t worry there is a reason for this, and that is that applications are running in the background that requires a lot of power. As well as using up a lot of physical power these applications can also be greedy when it comes to RAM and CPU usage which then leaves less space for Catalina to operate on, meaning that the OS will start to run slower.
If you want to stop these applications from using up so much power, you’re going to have to make use of the Activity Monitor. To find this program navigate to ‘Applications’ and then ‘Utilities’. Here you will see ‘Activity Monitor’, double click on it to open up the application.
Disable Apps that are Power Hungry
You will see a range of columns at the top, click on the ‘%RAM’ column to see all of the programs that are taking up a lot of RAM usage. If you find that you’re not using this application, then you will be able to click an ‘X’ in the top left corner of the screen and clicking this will stop the app. Likewise, if you want to see all of the apps that are taking up too much CPU, then click on the CPU tab and repeat the same process again to stop these memory hungry applications.
When you select the Quit Options this will, in turn, save any changes you’ve made during the time of the window is open, and don’t worry if the window takes a while to close this is totally normal, however if you select the option ‘Force Quit’ the window will shut down a lot faster but you will have lost all of the changes you’ve just made.
6. Double check that your Mac is fully compatible with macOS Catalina
As we have touched on before some Macs are not compatible with specific versions of the macOS. With every release of a new OS comes a whole new set of hardware requirements. Some of your macs out there might fulfil all of these requirements however some of you may not, and even if you try you will struggle to even use the Operating System it will be running at that slow of a speed, here is a lost of all the Mac devices that are supported by macOS 10.15 Catalina:
– Mac Pro (Late 2013 or newer)
– iMac Pro (2017 or newer)
– iMac (2012 or newer)
– Mac Mini (Late 2012 or newer)
– MacBook Pro (Mid 2012 or newer)
– MacBook Air (Mid 2012 or newer)
– MacBook (Early 2015 and newer)
– iMac Pro (2017 or newer)
– iMac (2012 or newer)
– Mac Mini (Late 2012 or newer)
– MacBook Pro (Mid 2012 or newer)
– MacBook Air (Mid 2012 or newer)
– MacBook (Early 2015 and newer)
If you’re Mac was made before any of the dates specified above unfortunately you don’t have the hardware requirements necessary to run macOS 10.15 Catalina and your only option is to upgrade your device with a SSD.
7. Moderate the User Interface Experience
One of the significant changes you might have noticed should you have already have upgraded to Mac OS Catalina is that the UI or User Interface looks massively difference, however with these changes comes some slowness in terms of speed. What we’re going to do now is the turn of QE/CI in Mac OS Catalina as features such as transparency will take up more of the resources of the computer, this, in turn, will leave less memory for Catalina to use resulting in a slower OS. To do this follow these steps:
Moderate the User Interface Experience
1. Go to “System Preferences” and then on “Accessibility”.
2. Next, go to “Display” and check the box next to “Reduce Transparency” and “Reduce Motion”.
2. Next, go to “Display” and check the box next to “Reduce Transparency” and “Reduce Motion”.
9. Create a clean installation file of macOS 10.15 Catalina
If you have got this far and find your macOS Catalina still running slow, this might be the option for you. What this does essentially is wipes off all the data on your hard drive and installs the macOS from a USB Insaller. This means that you have no old app junk, no third party applications or users accounts and all the settings are set to default.
Bottom Line
Hopefully, this guide will have given you all the answers you could have wanted should you have found yourself feeling frustrated at your system running slow after updating to the latest macOS 10.15, namely Catalina. This guide has also run you through all the possible reasons and solutions should you be having these issues and once resolved, you should be able to use the OS at an optimal speed.
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2 2 likes 77,017 views Last modified Jun 30, 2013 12:43 PM
Hello and Welcome to my User Tip
This is a bit more advanced topic to give those new to Mac/computers the information they need in regards to formatting, partitioning, installing, backing up, cloning OS X and Windows 7 in BootCamp.
Make sure to read this User Tip in it's entirely before doing anything, and/or ask questions on the forum as I might have missed something and it's a rather new User Tip.
Plan your actions ahead of time, discuss with others, get a clear plan and get confirmation before proceeding, data loss is possible and almost a certainty with instructions on this User Tip.
Also it's good to always have a Internet connection/browser on something to get help and review essential information + Tips.
If your here because of a slow machine, or problem and you think a 'back to factory' or a erase and install will fix it, it sure may just do that, but explore your repair options first as it might not require such drastic measures.
Also read for basic information also how computers work + Why is my computer slow?
If your here because of a data privacy issue, you can delete the offending files and 'scrub' them off the hard drive, or scrub free space or even delete the entire account (not OS X or programs in Applications folder), then scrub the drive.
If your here thinking a erase/fresh install will cure your slow computer performance on a hard drive, it certainly can do that, but you should consider this instead as it might not be required to have to hand install everything (unless the data is corrupted and you have no clean backup)
If your attempting to do this to restore your OS X back to 10.6 from 10.7/10.8, then you need to read this first to prepare your files:
If your here to turn over ownership, your in the right place, read on also followed by visiting for more details:
Are You Still Working So Late Mac Os Catalina
If you don't have your data backed up on other medium and need to perform data recovery efforts first:
If your here to experiment and learn how to go about things, then I suggest using a external drive with no essential data on it as a test subject.
If your here because Disk Utility says 'can't repair this volume' or you want to do a erase + fresh install of OS X, or your partitions are messed up, or there is a problem in the GUID, EFI or Recovery HD partitions you can't control, or your getting spinning beach balls and you've exhausted all other forms of remedy, then your in the right place.
![ARE YOU STILL WORKING SO LATE? Mac OS ARE YOU STILL WORKING SO LATE? Mac OS](https://i.pcmag.com/imagery/reviews/072luRXQ2YRUduKT7iWQpWS-16.1569480475.png)
What you will need if on 10.6:
- 10.6 Snow Leopard - clean scratches boot disk required. Use a tiny bit of rubbing alcohol and a clean soft cloth to polish.
- 10.6 has 2 types of disks: 10.6.0-10.6.8 colored machine specific only, w/free iLife suite (can't be used with another model).
- 10.6.3 Retail Disk for installed at factory 10.4-10.6.2 Intel processor Mac's. Macs that came new with 10.6.3-10.6.8 can't use.
- Get the free MacTracker for details about your Mac, essential for picking the right 10.6 boot disk version/RAM amount.
- Need a 10.6 disk? Call Apple via phone (only) to order these disks. Machine specific has free iLife, not on 10.6.3 white disks.
What you will need if on 10.7-10.8:
- 10.7 Lion, 10.8 Mountain Lion requires AppleID and password if installed via AppStore and/or to restore iLife.
- Warning! You need a strong, fast, reliable Internet download capability to reinstall OS X. 5Gb per second plus!
- 10.7-10.8 installed a 'Recovery HD' partition on the boot drive that acts like a boot disk. Use no 10.4-10.6 boot disks.
- 10.7-10.8 recent Mac's have Internet Recovery, is downloaded from Apple's servers for whole drive repair/format
- 10.7-10.8 upgraded Mac's with no Internet Recovery can use This Method their own or matching OS X version machine.
Wireless keyboards may not work with at boot key commands.
Use a wired USB one and PC keyboards may work. Windows key is the Apple command key, alt/option is the same, etc.
Some backup of data rules before you begin:
#1 Rule. Whenever affecting changes to the drive, make sure you have backups of all the data of all the partitions of the entire drive being affected and disconnect all other non-relevant drives (especially TimeMachine) to avoid mistakes and background automatic updates.
#2 Rule. Maintain two backups of your data on separate hardware at all times.
#3 Rule. Have at least one of those backups off site to protect against theft, fire, hackers, malware, estranged persons etc.
#4 Rule. Have your most valuable data burned to cd/dvd's archived/dated periodically offsite in case of slow creep issues and malware. Burned non-rewriteable cd/dvd's are naturally malware proof as they can't be changed later unlike other rewriteable media.
What's going on behind the scenes on your boot drive
This is the standard configuration of most Mac's boot drives and the order of the partitions on the drive.
GUID (hidden)*
EFI - firmware partition (hidden)*
Macintosh HD (visible)
BootCamp - Windows (if enabled, visible)
Recovery HD ('OS X base install', if on OS X 10.7+, hidden)*
*The GUID, EFI and Recovery HD partitions in most cases requires a complete drive reformat and/or OS X install to rebuild
GUID Partition Table
A boot drive with Mac OS X requires a GUID partition table, this is a small hidden section at the top of the drive that tells the hardware it's running on what partitions, where they are and what are on the drive. Erase this or it gets corrupted and like burning a treasure map, the locations to where the partitions are on the drive are lost, thus the data on those partitions are lost. (Well if it's not encrypted, software like Data Rescue on another bootable drive might be able to bypass the GUID and read the drive)
The way to rebuild this for most common users is to boot the machine via another bootable medium, or via a program residing completely in Random Access Memory (RAM) or by hooking the drive to another computer, because the entire drive needs to be reformatted and the partitions recreated along with a new GUID Partition Table (GPT)
By the way a partition is a section on the drive that is another volume, it can be formatted differently from the others, contain a bootable OS or just data.
EFI Firmware Partition
A boot drive with OS X requires a EFI Partition (also hidden) which stores data to be loaded or ran before the operating system you have chosen boots. This is what allows the at boot key commands, to allow basic operation of the machine if it's in Windows or OS X. If you start a Mac in verbose mode, you will see that the EFI is loading before OS X begins to boot up. Programs can be installed in EFI, it takes two reboots to activate them and is very difficult for many users to remove. So it's important to trust the source of your downloaded programs from the Internet sources. As since EFI is separate from OS X, has complete access to the hardware and Internet, there is no telling what's going on in there. Loading spyware in here is a rather trivial task for spooks and rather hard for common users to detect or remove.
To rebuild this requires a complete drive reformat from another bootable medium.
However if a firmware update fails to install, or at boot key commands (wired keyboard) fail to work, then it is possible to download the same firmware again from Apple's site on another Mac, burn a cd and install it.
https://support.apple.com/kb/HT1237https://support.apple.com/kb/HT2213
Macintosh HD Partition
This is right out in the open, next on the list order and usually named 'Macintosh HD' unless someone changed it. It contains OS X, programs and user accounts data. It can be erased from another bootable medium or volume with Disk Utility on it and a ability to install OS X back on.
You can also clone this partitions data (and it also does the Recovery HD partition for you) to another drive with software like Carbon Copy Cloner.
If your having problems with your machine, OS X can be reinstalled by itself without affecting most programs or your user account/files, also new user account can be created and the old one deleted and recreated with the hassle of a erase and fresh install . Step by Step to fix your Mac
BootCamp Partition
When installing Windows 7 in BootCamp, the Bootcamp software takes the bottom of the OS X Partition and works it's way up until it hits OS X data, then it stops and that's the limit of the partition your allowed to create.
![Mac Mac](https://cdn.mos.cms.futurecdn.net/GQzS29Y2YrtMbsjCKF5JqB.jpg)
You can clone this partitions data with software like WincClone 3 (runs in OS X) to another drive for backup purposes.
Changes to this partition should be undertaken by the BootCamp software, however Disk Utility can also be used as well as other software like WinClone 3.
When BootCamp software creates this BOOTCAMP partition, it's formatted MSDOS (aka FAT32) for later changing by the Windows installer to NTFS which Windows requires to be installed in. Apple Mac's can only read NTFS, can't format or write it.
I've used the BootCamp software to create the second partition for other purposes, then headed to Disk Utility to change the name of the partition and it's format, so that's a possibility for beginners if they are not well versed in creating additional partitions on their boot drive using Disk Utility.
If you can't create a partition big enough, you need to remove some OS X data to a storage drive and follow this procedure to shift the remaining data up further on the drive to make room for your BootCamp partition.
Windows is copy protected, if you reinstall or reverse clone and there is a hardware change (like you changed the internal drive to a larger one) then it's going to require jumping through their hoops to re-register it or it dies after 30 days or so.
Recovery HD Partition (OS X base install)
If you have OS X 10.7+, Apple installed this Recovery HD partition which one can hold command r down on a wired/built in keyboard and load this program into memory. It has Disk Utility, Safari, OS X Install and Terminal program. It's a troubleshooting environment to repair, reinstall, erase and install OS X. Plus do other things like reset the password, get online for assistance etc. It can only affect changes on the BootCamp and Macintosh HD partitions.
If for some reason this is deleted or not functional, newer Mac's have Internet Recovery where the same thing is loaded from Apple's servers by holding command option r keys down at boot time. A globe appears and it loads up. This is able to effect changes on the entire drive, including erasing the entire drive of all partitions and when OS X is reinstalled, it will recreate the required partitions and their information, provided the boot drive is still has a GUID and OS X Extended Journaled format.
If you have a older machine with no Internet Recovery and your Recovery HD partition is missing, you need to clone the OS X and Windows partitions each to their own separate blank drives and disconnect. Hold c or option/alt and boot off the 10.6 disk, use Disk Utility under the Utilities menu on the Installer page to erase the entire drive (with Security Option > Zero all data), make sure it has a GUID and OS X Extended Journaled (under Partitions) and quit then install 10.6. Reboot and Software update to 10.6.8, then reinstall 10.7+ from the AppStore using your AppleID and password. This will recreate your Recovery HD partition again, then you go and recreate the BootCamp partition (if you have it) and hold the option/alt key down to boot off the clone drive. Use CCC to reverse clone OS X, then run Winclone to reverse clone BoootCamp.
It is possible to clone the data of the Recovery HD partition and even create bootable USB thumb drives of it.
Disk Utility
This is Apple's program for erasing, formatting and partitioning drives and partitions.
#1 Rule, unless your going to completely erase the entire drive, do NOT use Disk Utility version on a older OS X (like a 10.6 boot disk) to affect repairs or changes to a drive with a later version of OS X on it. It's because the older Disk Utility doesn't know what it's looking at and newer OS X versions create changes to the GUID Partition Table (like Recovery HD) and EFI.
#2 Rule to repair/erase/format a drive or partition in Disk Utility requires being booted and/or running Disk Utility from some other medium that isn't on the same drive or partition being affected. Internet Recovery loads completely into Random Access Memory, so it's no on the drive being affected.
#3 Rule, don't use other drive format utilities as Apple does certain things with Disk Utility to make it all work.
Where you can find/use Disk Utility
Disk Utility in the OS X > Applications > Utilities folder is good for verifying the booted drive (but may make mistakes*), creating and changing other partitions on the same boot drive (but on not the Macintosh HD) and affecting changes on external drives.
*Some have used 'Verify' on their booted drives to discover problems, to be directed to boot from the Recovery HD/boot disk to Repair the drive, only to find nothing was fixed or required fixing. Affecting partition changes on the boot drive while booted from one of the partitions is risky, again have backups of the data before proceeding.
Disk Utility in 10.7+ Recovery HD - via the hold command r (wired or built in keyboard) upon booting (powering on) the computer. Can affect changes to the Macintosh and BootCamp Partitions, but not the entire drive.
Disk Utility in the 10.7+ Internet Recovery - via hold command option r (wired or built in keyboard + Internet connection, preferably a Ethernet cable to the router or modem power/off/on to reset) upon booting up (powering on) the computer on newer Mac's with 10.7+. Loads from the Internet into temporary Random Access Memory, turn off the power/reboot and it's gone. Can affect changes to the entire drive, including GUID, EFI and all other partitions.
Disk Utility on the 10.6 install disks - hold c or option/alt during boot up from this disk, Disk Utility is under the Utilities menu on the installer page after you select a language. Use with 10.6 and earlier formatted drives to repair or affect changes. Do not use to repair or affect changes on 10.7+ drives only to totally erase the entire drive.
Since OS X 10.5 is no longer being supported, I advise 10.5 user to consider upgrading your Intel processor Mac to 10.6 via the white Snow Leopard retail disks during this repair process. If you upgrade and its slow/problematic or you need to erase and install to fix a issue, see below for the link. Do not use the 10.5 Disk Utility other than for completely erasing a 10.5/10.6 machine even if it will hold c or option/alt key to boot from it I doubt it, the firmware may have been changed in 10.6 sometime to discourage booting.
How to use Disk Utility Artificial immunity mac os.
Here is a picture from a 10.6 version of Disk Utility, those on 10.7+ may be slightly different in appearance but work basically the same.
What's selected on the left is then changeable by the actions on the right side. Indented names are visible partitions on the drive above.
Depending upon what your booted from, depends what options on the right are enabled.
For instance I'm booted from my Macintosh HD partition and therefore cannot Repair that partition (grayed out)
If I booted from my Macintosh HD 2 partition (using option/alt for Startup Manager) then I could Repair my Macintosh HD partition.
If I wanted to erase or format my entire drive (selecting the drive makers name and size at the top) I cant do that because I'm booted from one of the partitions on the drive, so I would have to boot from another medium completely, like a program in RAM (Internet Recovery) or another boot drive/disk.
Note: If you keep First Aid: Repairing Permissions and it keeps fixing things, that's ok, Apple has just changed something in OS X.
Note: If Repairing the drive says it can't repair it, then there is a serious issue and the data needs to be backed up or recovered, then the partition or drive erased (hard drives use Security Erase > Zero, or one selection from the left on 10.7+ to map off bad sectors) and OS X reinstalled (if the Macintosh HD partition) or restored from a clean TimeMachine or clone backup.
Note: If you can't see your drive on the left, that's a pretty serious issue, especially if there are no backups of the users files.
If erasing a SSD, be noted that Disk Utility offers no secure erase function as SSD's have limited writes and to allow a secure erase would be abused and wear out the SSD prematurely. I have outlined a possible solution to overwriting deleted data on SSD's, however it's no sure proof method.
How to install OS X 10.6
Ok you all wiped clean and you want to install OS X 10.6.
If your hold c or option/alt key booted from a 10.6 install disk, make sure your entire drive is selected on the left, click Partition: Options: GUID and the partition format for OS X is OS X Extended Journaled, if not make it so. Quit and select the volume on the 10.6 installer and install it.
If you have a BotoCamp or other partitions on the drive, you can chose to erase only the Macintosh HD partition and install OS X there, instead of the entire drive.
When you boot up new, your greeted to the Welcome video and all that fresh setup business, you can use TimeMachine there to restore or migrate from a clone drive of 10.6 or earlier only.
If you need 10.6 disks, call Apple with your Apple Menu> About this Mac > More Information > model number like 'MacBook Pro 1,3'.
Mac's that came originally from the factory with 10.6.3 or later cannot use the 10.6 white Snow Leopard retail disks, these require machine specific disks only available used (must be the same exact model Mac) /or via calling Apple via phone.
How to install OS X 10.7+
Ok you either erased the entire drive, it's blank, or you erased just the Macintosh HD partition. Now all you have to do is quit Disk Utility and install OS X using your AppleID and password right from Recovery HD or Internet Recovery your already booted into.
You will need a fast and reliable Internet connection as OS X is now downloaded, not on the computer or drive.
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