One of the greatest sources of confusion for computer users is the difference between a computer’s memory and its storage space. The confusion is not entirely the users’ fault. Overlapping terminology contributes as does poor word choice. I’ll try to reduce confusion by differentiating the terms as well as talking about their overlap.

A classic example of this confusion is when a person receives an error message which states something about insufficient memory and the person thinks that they need to delete files from their computer to make more memory available. This is  not the right action to take. Taking the error message at its face value, the proper response would be to close applications and files to free up memory. Alternatively, one could buy more memory for the computer. Let’s start to examine these terms.

Computers have two kinds of storage — temporary and permanent. A computer’s memory is used for temporary storage while a computer’s hard drive is used for permanent storage. Whoever selected the term memory for temporary computer storage did the world a disservice since people tend to permanently store information in our memories. If I asked you to recall your first grade teacher’s name, you could, most likely, tell me because that piece of information is stored in your memory, right? This is not how computers use their memory. A computer’s memory is also called RAM which is an acronym for Random Access Memory. A computer’s memory is where information is temporarily stored while it is being accessed or worked upon. For example, if I’m updating my resume, then I double-click its icon to open it. This process of opening the file, copies it from its permanent home on the computer’s hard drive, into the computer’s memory. Once in memory, I can edit it. If the computer loses electrical power while I am updating my resume, the most recent changes I’d made would be lost. This is because, the information in a computer’s memory is only kept there while electrical power is supplied. To avoid losing my most recent changes, I would need to save the file. The act of saving a file copies the file back to the computer’s hard drive. The contents of a hard drive remain intact even if the computer is turned off or it loses its electrical power some other way.

A simple analogy I use to help remember these terms is that memory is like your desk’s work space and your hard drive is like a filling cabinet. Your filing cabinet is typically large enough to store hundreds of file folders and thousands of pieces of paper. Your desktop work space is not large enough for all of these file folders and papers.

Both temporary computer storage (memory or RAM) and permanent computer storage (hard drives) are measure in bytes. These days they are measured specifically in gigabytes (GB). If you’d like to learn more about bytes and gigabytes, please read this previous Tech Tip. This overlap in measurement systems contributes to some of the confusion.

In early 2012, a new Mac might be equipped with 4 GB of memory and a hard drive whose storage capacity is 500 GB. The primary reason for this great disparity is cost. Memory, RAM, is much more expensive then hard drive storage space. Here’s a rough comparison. 1 GB of RAM costs about $8 while 1 GB of hard drive storage space costs about 10 cents. In other words, RAM costs about 8000 as much as hard drive storage space. Wow.

This price differential explains why we can have much more hard drive storage space compared to memory (RAM) storage space, but why do we need both? Why are computers designed this way, constantly copying data back and forth, into memory and then back to the hard drive? The primary reason is that RAM is much faster then hard drive storage space. I don’t have exact number,s but RAM is thousands, probably tens or hundreds of thousands of times faster then a hard drive. This is true for both mechanical hard drives, which have been used for decades, as well as solid-state drives (SSDs) which are becoming increasingly common. Apple uses SSDs in all iPhones, iPads and MacBook Airs. SSDs are an option in the iMac, at present.

The prevalence of confusion between (temporary) memory and (permanent) hard drive storage space is so great that the occurrences of misuse of these terms is greater then the proper use of these terms. For example, a discussion from January 2012 is about how much memory is enough in an iPhone. The original poster’s question should be how much storage space is sufficient in an iPhone. It’s tough to use these terms correctly when so many don’t. I feel like a fussbudget grammarian when I correct a person or clarify a person’s question. Now that you have a better understanding, help me out and use the terms properly!

Note: Since I’m a strong advocate for everybody backing up their computer’s hard drive, I should point out that hard drives should be thought of as only semi-permanent storage. This is because hard drives fail. Every hard drive will eventually fail. It’s only a matter of time. Drives can fail in a number of ways so some fail sooner then others. Sometimes they give warning signs and other times they don’t. Consequently, it’s necessary to backup the contents of a hard drive. Ironically, we often backup one hard drive onto another hard drive! In previous Tech Tips, I’ve recommended backing up your data to at least two different drives and haivng one copy of your data stored in an off-site location.

A few months ago a representative of Stellar Data Recovery contacted me and asked if I’d be interested in reviewing their product Stellar Phoenix Macintosh, a data recovery application. I was happy to oblige. At long last, here’s my assessment.

If you’ve read many of my tech tip articles you may know that I’m a staunch advocate for setting up robust, redundant and automated data backup systems. If one has such systems in place then one’s likelihood of actually needing a tool like Stellar Phoenix Macintosh should be slim. However, the need for such tools can still arise for a myriad of reasons. Maybe one hasn’t yet copied photos from their camera’s SD storage card to their computer. Maybe one uses a USB flash drive to move files around and doesn’t backup this drive. Maybe one’s backup is misconfigured and it isn’t actually backing up an important folder. Any such drive could fail or a user could accidentally delete a file. Thus, anybody could end up needing a data recovery tool such as Stellar Phoenix Macintosh.

Stellar Phoenix Macintosh has a simple user-interface which includes buttons to let you try to recover data from various types of drives including iPods. It also has a button dedicated to photo  recovery. Within the main Drive Recovery section it provides options to try to recover deleted files, files from re-formatted drives and from drives which don’t mount. I happened to have two non-mounting drives sitting around. One was an external firewire hard drive and the other was a USB flash drive. Both were personal drives which I’d used for years. They’d each stopped working properly in the past six months. Nothing critical was on either drive so I’d only made half-hearted attempts to figure out what was wrong with the drives previously. I’d been unable to get either drive to mount. Not surprisingly, Stellar Phoenix Macintosh wasn’t able to see them or recovery any data from them. I didn’t really expect that it would since I suspect that there were physical problems with the drives. If I had really needed to get data from these drives I would have sent the drives to a professional data recovery company, like Drive Savers which has a strong track record of being able to recover data.

Next, I took a fully-functioning external firewire drive that contained a backup copy of some of my music and movies. I put all of my files into the Trash and emptied the Trash. Then I asked Stellar Phoenix Macintosh to try to restore the files. I used it’s Deleted File Recovery feature. I showed it the external drive and I let it scan the entire 60 GB drive. Understandably, this is a time consuming process since it needs to scan every block. I don’t know how long it took since I went to bed, but I’m sure it took more then an hour. By morning it had finished, but I didn’t have time to finish restoring my files so it conveniently let me save the scan file, presumably some sort of directory of the drive. Subsequently, I used Stellar Phoenix Macintosh’s Resume Recovery feature. This let me pick up where I left off.

Stellar Phoenix correctly listed the folders which I had deleted. I started to navigate through this folder list and it correctly listed the names of sub-folders and sub-sub-folders. What was annoying was that Stellar Phoenix’s window could not be re-sized. Additionally, the 3 sections within it’s window could not be re-sized either. This made it cumbersome to navigate through the folder hierarchy. This is a significant short-coming of the application’s user-interface. Up to this point, I’d like the interface. It had been simple, buttons well labeled and explanations of their function were frequently listed on screen. So it was quite jarring and annoying to suddenly realize that I couldn’t resize the window at all. However, I continued with the data restore. I selected about 10 mp3 files as well as a number of PDF documents and Microsoft Word files. I clicked the Recover button, waited a few seconds and the files were saved to a new folder on my Mac’s Desktop. I was then very disappointed when I tried to open these files and not a single one could be opened properly. I’m not sure why. Stellar Phoenix had done an admirable job of seeing the deleted files as well as their file names and folder structure. All of this is important, but it failed in the final and most important step of successfully recovering the files.

I wanted to give Stellar Phoenix another chance so I took a healthy 1 GB USB flash drive, formatted it, copied a few files onto it and then deleted them a few minutes later. I then had Stellar Phoenix scan the drive which took about 10 minutes. It was not able to recover the folder structure or the file names, but it did create folders for each type of file which it found. In other words, it created folders for PDFs, JPEGs, Word and RTF files, for example. I then asked Stellar Phoenix to recover the files. It did so and all of the files opened properly. I was pleased with the results in this simple test. I should mention, however,  that in a real world situation in which one might need to only recover a few files from a hard drive that has been used for years, the inability of data recovery software to recovery filenames and folder structures can mean that one could have to spend a fair amount of time locating the few desired files from a larger pile of recovered files.

In conclusion, Stellar Phoenix could be useful as a data recovery tool, certainly for recently deleted files and possibly in other situations. However, the lessons that I take away from these experiments are that data recovery is not always possible. Even when it is possible it can be time consuming to conduct drive scans and then locate the particular files you need. If you need to employ a professional data recovery service, it can be very expensive. Thus, I think it’s more prudent to setup, monitor and test robust, redundant and automated backup systems so you can hopefully avoid having to rely on data recovery products.

You have choices when you want to re-use, recycle or destroy a hard drive. Let’s look at a few common scenarios to review these choices.

You have a computer that you want to retire or give to somebody else.

In this situation, the hard drive works properly you just want to securely erase your data before you give the computer to another person. Thus, you want to securely erase the hard drive and then reinstall Mac OS X. Follow the instructions in my previous Tech Tip article on how to securely erase a hard drive. If you don’t want to do this work yourself, you could take your computer to an organization like Interconnection orTotal Reclaim. Both of these organizations offer free data wiping of all hard drives on donated computers. I tend to use Interconnection as much as possible since they are a non-profit group that does their best to re-use the computer while Total Reclaim is a for-profit company which focuses on recycling computers and other electronics.

You have either an external hard drive that you want to re-use or sell, but first you want to remove all of your personal data from it.

This is very similar to the first situation. The hard drive works properly and you want to re-use the hard drive. Thus, you should securely erase the data from the hard drive using the instructions in my previous Tech Tip.

You have a hard drive that died that you need to get rid of but you want to make sure that nobody can ever get any of the data on that hard drive.

Since the hard drive is not working properly we can’t securely erase the hard drive as described above. Instead, the hard drive will need to be destroyed. You could either do this yourself or have somebody else do it. If you want to do it yourself you could secure the drive in a drill press and drill a few holes through the drive. This would destroy the circuit boards and, most importantly, the platters containing your data. If you want somebody else to destroy it then I recommend using an organization like Interconnection or Total Reclaim.

Do you need to recover files that were deleted from a Mac’s hard drive? Here’s a quick overview of three options.

Option 1 – By far the easiest way to recover a file is to restore it from the most recent backup. This is why I’m such a strong proponent of setting up a comprehensive backup system including automated TimeMachine or CrashPlan backups. By default, TimeMachine runs every hour and CrashPlan runs every 15 minutes. Here’s are tech tips I wrote about how to restore files from Time Machine and CrashPlan backups.

This option is appropriate for a wide range of situations including: accidentally deleting a file and realizing it a minute or a month later; suffering from a malfunctioning hard drive, losing your computer or having it stolen. Assuming that you make multiple and frequent backup copies of your data this option has a very high recovery success rate.

This is the last of the good options. The two remaining options are either expensive, time consuming or have a much lower chance or success — or some combination thereof.

Option 2 – Use data recovery software such as ProSoft Engineering’s Data Rescue. Data Rescue and comparable applications can search a hard drive for deleted files and it can try to search a malfunctioning hard drive for files. Both of these processes can take hours to run and their success is far from guaranteed. When a file has is deleted it’s not really removed from the hard drive. Instead, the entry for that file is removed from an invisible list of all files and the space where the file resides on the hard drive is marked as available for re-use. Depending upon how much time has elapsed since the file was deleted it may or may not have been over-written. If a hard drive is failing who knows if you’ll be able to recovery any files from it.

Option 3 – Use a professional data recovery company like DriveSavers. DriveSavers has been around since the mid 1980s. They have a stellar reputation and success rate. In the rare cases that I’ve had a client who needed professional data recovery, I’ve often used DriveSavers and they have fortunately been able to recover most of the needed data. The downside of professional data recovery companies is the relatively high cost.

In the past decade, I’ve only sent two hard drives to DriveSavers. One hard drive was from an Mac made in the mid 1990s. It hadn’t been used in years and my client suddenly realized that she needed some data from it. The hard drive no longer worked properly. She spent about $2500 to recover a few dozen files which she needed.

In the other instance, a woman phoned me after most of her iPhoto Library suddenly vanished before her eyes. She didn’t have any backup of the hard drive so we sent the hard drive to DriveSavers. She paid about $1500 for the recovery work. DriveSavers recovered thousands of jpeg photos, but some of them were random clip art files so my client then had to spend countless hours weeding through the recovered files.

In my opinion, options 2 and 3 aren’t really attractive options. They are expensive, time-consuming and the odds of getting all of the files needed are not as high as I’d like. In comparison the cost to buy a couple of backup hard drives or to pay for CrashPlan’s online backup storage system is much less. Please setup an automated, redundant and reliable backup system for your Mac.

Do you want to clean up your Mac hard drive? Is your hard drive nearly full and you don’t know why? OmniDiskSweeper (free) can help with both of these situations. OmniDiskSweeper will scan all files and folders on your Mac and then list them by size, starting with the folders taking up the most space. This helps you to focus your clean-up efforts on the folders that are taking up the most room on your Mac’s hard drive.

People often erroneously think that their Mac is running slowly because the Mac’s internal hard drive has so much stuff on it. This is rarely the case. Unless the hard drive is 90% or fuller then the computer’s performance is not impacted by the amount of stuff that is stored on the hard drive. I should be clear to mention that when the hard drive is nearly full, typically starting around 90% full, that the computer’s performance is significantly impacted. So, if your hard drive is this full then please download and use OmniDiskSweeper to help you clean it up.

OmniDiskSweeper conveniently shows you all of the invisible files and folders on your Mac. Over the years, I’ve seen several hard drives that were filled with spurious log files or errant backup copies of data — all of which happened to be invisible. These invisible files and folders are part of the Mac operating system, Mac OS X. Some of them are critical files so don’t throw away any invisible file without being sure that you have a full, bootable backup of your Mac and that you know what you’re doing. If you’re unsure check with a Mac expert or hire a Mac consultant.

Using OmniDiskSweeper is easy.

• Download OmniDiskSweeper and install it in your Applications folder. Double-click it to open it.
• Then, from the list, select a hard drive which you want it to scan. OmniDiskSweeper uses the term sweep to imply scan. The scan can take 10-15 minutes or longer, depending upon how much data you have.
• When the scan is complete you’ll see a columned window (see below) listing all folders sorted by size.
• If you’ve identified a file that you want to delete you can select it in the column browswer window and then click the “Delete” button in the lower left corner.
• If you want to look at a file or folder then select it in the column browser and double-click the icon in the lower-right corner. This will reveal the file or folder in the Finder so you can look at it more closely.

Happy hunting. I use OmniDiskSweeper regularly and find it an indispensable tool for cleaning hard drives.

OmniDiskSweeper File Browser

Here are instructions on how to use Disk Utility to securely erase a hard drive connected internally or externally to your Mac. These instructions were written for Mac OS X 10.4 to 10.6. The process is very similar on older versions of Mac OS X but the screens will look a bit different.

Requirements – You’ll need either the Mac OS X install disk that came with your Mac or another OS X install disk that’ll boot your Mac, such as a retail copy of the Mac OS X 10.5 or 10.6 install disk.

I recommend securely erasing a hard drive before you recycle it or give it away. The instructions below include the option to re-install Mac OS X onto the hard drive at the end of the process.

If you’re securely erasing an external hard drive you do not need to use a Mac OS X install disk. Instead, you can simply open Disk Utility which you’ll find in the Utilities folder inside the Applications folder. In Disk Utility, select the external hard drive and then follow the last few steps below to erase it using one of the Security Options described below.

Background – Technically, it’s not possible to erase or remove data from hard drives. Thus “securely erasing” is a misnomer. Instead, what we’ll be doing is over-writing the data on your hard drive with gibberish, a random string of bits of data. When you securely erase your hard drive you’ll have a choice of how much over-writing you want to do. This process can take many hours if you select the 7-pass overwrite procedure. I recommend starting this process and then letting it run over-night.

• Insert the Mac OS X install disc that came with your Mac.
• Note: The disc will begin the process of installing Mac OS X on your Mac. Whether or not you actually choose to install Mac OS X is your choice, but if you do, you’ll do it AFTER you’ve securely erased your Mac’s hard drive.
• Select your preferred language from the list presented.
• When you see the welcome screen for the Mac OS X Installer go to the menu named Utilities and select Disk Utility
• In the left pane of the Disk Utility window, click on the hard drive you want to erase.
• In the right pane of the Disk Utility window, click the Erase tab.
• Click the Security Options button
• I recommend that you select the 7-Pass Erase options, but you could choose the 35-Pass Erase option. Here’s my description of these options.

Don’t Erase Data— This option does not provide any security. This option only over-writes the directories on the hard drive. Your files could still be recovered.
Zero Out Data— Provides a pretty good level of security. All of your files are over-written with a string of zeroes. There are forensics utilities that in theory could retrieve some data.
7-Pass Erase— Provides a lot of security. This is considered sufficient by government standards to erase data from a disk. It writes a random string of ones and zeroes over your data files seven times. It may take several hours or more to complete this process.
35-Pass Erase— Provides the maximum amount of security offered.This option takes an extremely long time, possibly more than one day.

• Click the radio button in front of 7-Pass Erase
• Click OK.
• Click the Erase button next to the Security Options button.
• Confirm you want to erase and the process will be begin.
• If you want to install Mac OS X then go to the Disk Utility menu and select Quit
• You’ll be taken back to the Mac OS X Installer welcome window. Click Continue.
• Agree to the software license.
• In the “Select a Destination” window click on the icon for the hard drive which you just erased and then click Continue.
• Click the Install button to start the installation process. Depending upon the speed of your Mac and the version of Mac OS X which you are installing this process could commonly take anywhere from 20-60 minutes.