Okay, so I have a late 2013 model retina macbook pro. A couple a days ago i placed a sensitive file on the desktop, and later deleted it by emptying the trashcan. I then read that was not the way to get rid of a sensitive file. I still have a copy on the file stored, on my other computer, and I was wondering if putting the same file in the same place (the desktop) would overwrite the old file I had deleted which now is allocated as "free space". I can use disk utility because I have an SSD. Then I can do a secure delete in order to erase it completely.
MacBook – Secure delete an erased file using same file
copy/pastedeletingmacbook propathsecure-erase
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I'm going to start off backwards. 4k Display will require some sort of cable, wether DVI, Display port, or Thunderbolt that is from manufacturer to manufacturer and model to model different. According to the tech specs of 4K it is compatible with Display port 1.2.
According to : http://www.apple.com/macbook-pro/specs-retina/
"Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to 2560 by 1600 pixels on up to two external displays, both at millions of colors"
This could however simply be that Apple has only tested it on displays with that resolution and once 4k displays are out in the real world people can test it.
So your MBP Retina can support 2 external displays and the use of the the clamshell display at the same time. Those external display can be attached via HDMI and Thunderbolt (adapters) or both via Thunderbolt adapters. But so far the tech specs limit the resolution to 2560x1600. It could also be that the resolution output could be enhanced with a software update (firmware update) at a later time.
Archived Specifications page:
Not so much that it's not necessary...
I'm a couple years late to the party, but it might be worth pointing out that Apple (who has now entirely remove "Secure Erase" options from the Disk Utility app) hasn't really removed the option because it "isn't necessary" — according to its El Capitan security release notes, they did it because they can't guarantee a secure erase:
Description: An issue existed in guaranteeing secure deletion of Trash files on some systems, such as those with flash storage. This issue was addressed by removing the “Secure Empty Trash” option.
Glenn Fleishman, gives a good overview of this in "How to replace El Capitan's missing Secure Empty Trash." The fact that, currently, the only DoD/NSA approved SSD sanitation procedure is smelting or shredding the drive into a fine powder somewhat echoes the challenge in being able to wipe a drive, for sure.
It is pretty difficult to recover data from an SSD...
As Trane Francks explained, recovering data from an SSD is, by default, pretty difficult. The data isn't necessarily encrypted, but it is distributed data over many locations in order to perform as few writes as possible to a single location (both for performance and for drive longevity). So once data is deleted, find the place a file used to reside in is like putting together a multi-million piece jigsaw puzzle (all before any garbage collecting the drive may decide to do). It is possible to recover files from an SSD, but this usually requires a lot of extra effort.
To make it hard for recovery tools...
Encrypting a SSD with any kind of suitably secure key, and then erasing that key, makes it virtually impossible to recover any data. This can be done, on a Mac, by enabling FileVault, booting into recovery mode, unlocking and then deleting the drive with Disk Utility.
If you're just looking to make sure stuff is securely erased without nuking existing data, you could try using the diskutil terminal command — the command line version of DiskUtility, wherein secure erase options have not been removed:
sudo diskutil secureErase freespace 0 "/Volumes/[Disk Name]"
This should attempt to write and delete a couple tempfiles which will fill up the entire hard drive. In doing so, every available space should be filled and then cleared.
Good information on all these options can be found in "How to Securely Erase a Mac SSD".
Also, you can always try to run some data recovery tools to see if there is data that is still immediately available.
Best Answer
There is no way to guarantee to put the data in the 'same place', no matter where in the filesystem you put it.
Hard drives just don't work that way. They will put specific data anywhere they like [or to an algorithm unfathomable to mere users]
To be reasonably certain of overwriting the data [with as much certainty as you can have without destroying the drive] you would use Erase Free Space - which you will have noticed you cannot do on an SSD - though the way SSDs use their storage is completely unlike a HD; they try to allocate writes all across their memory-space to even out the wear. This makes recovery of a deleted file a much more difficult task than with an HD, but not impossible.
As far as I'm aware [& nothing ever seems certain in these things] the best way to 'erase free space' on an SSD is to fill the drive with random data - anything, a movie file copied over & over til the disk is full, then delete it all again.
That will have written over the previous data at least.
Repeat ad nauseum for multiple pass erase [if that even really has any meaning for an SSD.