In this lesson from our full tutorial on Mac Utilities see how to erase or reformat a hard drive with Disk Utility. Learn more at www.TheMacU.com.

Erasing free disk space is an easy (albeit not quick) way to help prevent the recovery of files you have erased from your system. Conventionally when files are deleted from storage device, the system only removes their entries from the file system's directory, thereby flagging blocks containing the data as being free to use. While this offers a quick way to delete files from the drive, the data is technically still intact on disk and thereby leaves open the possibility for recovery using special software.

To reverse the plotting order, do one of the following: For categories, select the Categories in reverse order check box. For values, select the Values in reverse order check box. How to do reverse order for scatter plot in mac numbers. Or you may have meant that you wanted to reverse the order of values shown on the X axis, so that 0.3 was at the left and 0.063 at the right. Numbers always arranges a scatter chary with values increasing toward the right and toward the top, so reversing the order requires some manipulation of the data and some manual labeling. Click a scatter chart or drag one to the sheet. Click the Add Chart Data button near the chart. If you don’t see the Add Chart Data button, make sure the chart is selected. Select the table rows or columns that have the data you want to use by clicking the numbers or letters for those rows or columns. I need to create a graph with 2 x-axes and 1 y-axis (which is shown in reverse order). I have triple and quadruple checked that the correct columns have been selected. Ice age is primary-- it has the correct y-values, but not x-values. Gas age is secondary-- it has the wrong x and y values. I suggest the plotting order be reversed, so that more important series can be listed first in the legend and appear over other curves in the plot area. This post is a suggestion for Microsoft, and Microsoft responds to the.

To prevent this from happening, one option that Apple has offered in OS X is to erase the free disk space using Disk Utility. This option writes zeros to the unused portions of the drive and overwrites any previously deleted files. This option makes it nearly impossible for the drive's heads to be used for reading any residual magnetism patterns and recover files. Instead, any remote possibility of data recovery would require dissection of the drive and the use of specialized equipment that can detect residual magnetism. The option to erase free disk space might be disabled on newer Mac systems. Screenshot by Topher Kessler/CNET Even with using specialized equipment, such a procedure would only increase the slim possibility of data recovery, so using Disk Utility to erase free space does have its security benefits; however, if you have purchased a new Mac system or upgraded your hard drive, then you may find Disk Utility no longer offers this as an option.

If you find this is the case with your system, and Disk Utility only shows the Erase Free Space option as being grayed out, then it is likely the reason is because your Mac is using an SSD as its primary storage device. Solid-state technology has the benefit of being exceptionally fast; however, the storage blocks in the NAND memory chips have a finite number of write operations that can be performed before they will no longer hold data reliably.

To combat this problem, SSD manufacturers implement techniques called 'wear leveling,' which distribute write operations through the available memory chips and extend the life of the drive by ensuring they all get used evenly. If you were to erase the free disk space on an SSD, you would force the system to unnecessarily write not only to locations where data previously was stored, but also to fresh locations on the drive that have not yet been used. Overall this would just wear out the SSD faster and result in a premature degradation of the drive's performance.

In addition, such an operation might cause your system to no longer work properly. On some SSD drives, once data is written the system will need to perform operations to free it. These procedure can take a little longer than both the read and the write operations themselves, and in the mean time the drive might report to the system that it no longer has any space available to store data, which can result in your system booting slowly or not being able to boot at all. To avoid these problems and to keep your SSD as fresh as possible for the long term, Apple has disabled Disk Utility's secure erase option for some SSD devices.