Here’s an interesting submission from a reader:
My Dad got a new computer last week which he had me help set up and configure. One of the things I noticed was that the 40GB hard drive he ordered didn’t seem to be as large as advertised. I checked the drive by accessing Properties in My Computer; his hard disk showed a total capacity of somewhere around 34 GB. When we checked the Hardware tab and looked at the properties of his hard disk there, it showed something like 3 partitions — one of which totaled to about 38 gigabytes. We called the computer maker’s technical support department to find out why the 40GB drive never seemed to show a capacity of 40 GB and the answer we got was a rather vague: “Some of the disk space is taken up with system files which you can never see in Windows so you’ll never see the whole 40 gig as being available.” The person sounded like they were reading off a FAQ screen, and trying to clarify the issue didn’t get anything more useful out of them. What’s really going on?
There are several factors at work here:
While you can rarely purchase an unformatted hard drive these days, many drive manufacturers continue to advertise the unformatted capacity of their products, not the more sensible usable formatted capacity. The low-level formatting usually completed by the manufacturer records thousands or millions of pieces of data throughout the drive to mark positions of tracks and sectors — roughly analogous to searching for words in a book by chapter and page. High-level formatting accomplishes a similar task but for specific file systems — such as FAT16 (DOS), FAT32 (Windows 95/98), NTFS (Windows NT), UFS (Unix), MFS and HFS (Apple Macintosh), and others — and creates space for storing special file attributes such as hidden, read-only, and directory statuses.
Not surprisingly, all that formatting can take up about 5% of your unformatted disk capacity. Your 40GB drive is now 38GB.
Most name-brand computer manufacturers — including Dell, HP, and IBM — cut costs by sending out computers with no setup disks, CDs, or manuals. The installation disks for the bundled software — the operating system; the free software of typical giveaways like Quicken, MS Money, and MS Works; the proprietary drivers to make the CD, sound card, and printers function properly — are all stored on a special, usually invisible partition (a separate data storage area) on the hard drive which usually boots only the first time you turn on the computer. This partition is not normally compatible with mainstream operating systems, and cannot be detected by them without a special utility.
When the computer is first booted up when unpacked from its shipping box, the installation programs for the software packages are then either executed directly from the phantom partition or copied over to the hard disk for later installation. This special partition is very rarely removed during the installation process and usually remains, often taking up several gigabytes of disk space. This is really a great feature because the phantom partition can often be used to restore a completely messed-up system to factory defaults by inserting a special restoration diskette disk or CD available from the computer manufacturer’s support department.
Thus, your previously 38GB drive is now sized between 34 and 36 gig. Keep in mind that this factor only applies to primary (or first-position) drives purchased at the time of manufacture of a major brand-name computer; extra secondary drives purchased to expand your system’s storage capacity do not contain the phantom partitions.
Gigabytes vs Gibibytes
The least known and potentially most insidious factor stems from less-than-honest (or hopefully just plain ignorant) marketing departments. If you examine the fine print of many advertisements, whether printed or broadcast, you will often see printed a definition of megabyte (MB) as 1,000 kilobytes (KB), or a gigabyte (GB) as 1,000 megabytes — this conforms with the standard metric system and is accurate.
However, the disk usage displayed in the operating system’s user interface is usually calculated using powers of two; a kibibyte (KiB) is actually 1,024 bytes, a mebibyte (MiB) is 1,024 kibibytes, and so on. The difference in decreases conceptual storage space by 2.4%.
If all of the above factors apply to a particular 40GB drive in the extreme, it could show only 32GB of free space! And that’s why your 40GB drive may not be a 40GB drive after all…