How can I remove disk1 and macos x base system from HDD?

You do not want to remove this. mac os x base system is the a part of the recovery disk. I do not recommend deleting any of these unless you really want to

BUT if you wanted to do something crazy, here is the terminal command to show hidden partitions (which you then can delete and do what you want);

defaults write com.apple.DiskUtility DUDebugMenuEnabled 1

Show & Mount Hidden Partitions with Disk Utility in OS X <-link

First you need to turn on the debug menu:

• Quit out of Disk Utility, and launch Terminal to type the following defaults write command:
  

  defaults write com.apple.DiskUtility DUDebugMenuEnabled 1

• Relaunch Disk Utility and look for “Debug” to appear alongside ‘Help’
• Click on the new Debug menu and pull down and select “Show every partition” so that a checkmark appears next to it

• Now the hidden partitions will displayed alongside mounted visible partitions, but they will appear grey rather than black
• Right-click on the greyed out partition to mount and choose “Mount [Drive Name]“

That means its mounted right now.

To umount it.

Resetting PRAM and NVRAM

1. Shut down the computer.
2. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on the computer.
4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
6. Release the keys.

This should get rid of the "Mac OS X Base System" virtual mount.

It should be your Mountain Lion recovery image. Its compressed to start the recovery if needed. It was present before in Lion, just wasnt mounted at the time.

Either way, its not doing damage and its pretty insignifacant in size.

Hopefully this helps you out!

whitewater2 solved my issue with the PRAM and NVRAM reset trick. I've been searching for a solution to an issue reinstalling the Mac OS on an older iMac for a while now. After I noticed there was an Apple disk image Media device for El Capitan in Disk Utility even when booting, even when trying to boot with an older OS install CD, I searched and found this forum.

Thanks whitewater2!

I just sign up on this page to say Thank You m8! I was really desperate and you save my life! All Hail Whitewater2

Glad it worked out for ya!

The screenshot is a general one, but shows disk0s1

From a previous post that might give you more insight as to why to not mess with it;

http://apple.stackexchange.com/questions/22941/what-is-the-mac-os-x-base-system- disk-image-on-my-2011-macbook-air

"It's rather complicated, and actually a lot of the complexity is to avoid wasting space; I don't think you can "reclaim" anything without breaking it.

Let me start at the beginning: your hard drive (/dev/disk0) has two relevant partitions: Macintosh HD (your regular startup volume), and Recovery HD.

Recovery HD is marked in the partition table with the type Apple_Boot, but is actually in the normal HFS+ format. It contains minimal booter files and kernel, and at /com.apple.recovery.boot/BaseSystem.dmg, a disk image with a stripped-down and tweaked copy of OS X. The booter mounts this volume (it attaches as /dev/disk1), and transfers to OS X running on it. This is the Mac OS X Base System.

Notice that the Recovery HD is only 650MB, but Mac OS X Base System is 1.4GB? That's because it's a compressed disk image (and I'm pretty sure that compression is the reason they bother with all this disk image trickery). Actually, BaseSystem.dmg is compressed down to only 451MB (at least in OS X v10.7.0).

Also, the volume naming is somewhat inconsistent. You've got /dev/disk1s3 named "Recovery HD", but for some reason it's mounted as "/Volumes/Image Volume" in recovery mode. BaseSystem.dmg has a volume named "Mac OS X Base System".

So that's disk0 and disk1; what about the rest? I'm not certain, but I'm pretty sure they are RAM disks to save temporary data in folders OS X modifies as it runs (remember that in recovery mode, you're running from a read-only disk image). Running the

mount

Why ?

yes, that it what its sole purpose of it if it cannot restore from a regular image.

Thank you for your help! It saved my day:)