2000: When you partition a hard drive, each partition functions as a separate volume and appears on your desktop with its own icon and name. I’m a fan of hard drive partitioning and have had four partitions on the 500 MB hard drive in my PowerBook 5300 and on the 2 GB unit in my PowerBook WallStreet G3.

What are the advantages associated with partitioning a hard drive? Well, prior to the introduction of Mac OS 8.1, the most compelling reason to partition was that it could gain you a substantial amount of hard drive space, especially on larger drives.

More Efficient Allocation of Drive Space

The old Macintosh hierarchical file system (HFS)* divided each volume into approximately 65,500 blocks, which represented the highest number of data units that could theoretically be stored on the drive – no matter how large it was. This was not much of a problem back in the days when an 80 MB drive was considered large. However, as hard drive capacities expanded to 500 MB and beyond, the minimum file size, even for documents with just a couple of lines of text in them, became unreasonably large.

The solution, before Apple introduced its extended file system (HFS+)** with Mac OS 8.1 in January 1998, was to partition the hard drive into several smaller volumes, each with a smaller block size than the original single volume. For example, when I partitioned my PowerBook 5300’s 500 MB hard drive into four partitions, I instantly gained more than 30 MB of usable storage space.

Other potential advantages provided by hard drive partitioning are slightly faster drive access, because the drive heads don’t have to traverse as far to find a file within a smaller volume, and enhanced organization, for people who like to keep one kind of file – say documents – in one drive partition and applications in another.

Also, should one partition become corrupted, the possibility exists that the other partition or partitions may not be damaged, and data on them will be recoverable.

The Emergency Partition

Speaking of troubleshooting and hard drive corruption problems, having a backup operating system installed on a partition separate from the one where your normal working system resides can be very convenient when you suspect system problems. Just boot from your alternate system, and if the troubles disappear, you can be pretty sure of your diagnosis and take remedial action.

Another advantage of having operating systems on several partitions is that you can keep different versions of the Mac OS handy. For example, I normally run Mac OS 9 on my WallStreet, but I also keep a copy of Mac OS 8.1 on another partition, which is very useful when I occasionally have to use older software that is not supported by Mac OS 9.

Data Security

A potential security advantage of partitioning is that on a computer that is used by several people or installed in an insecure location, you can assign separate passwords to each partition, denying access to one more partitions when the computer is being used unsupervised.

Not As Helpful with Small Drives

A potential downside to partitioning is that if you have a relatively small drive and frequently work with large files, you may find it a drawback. Some people also find the concept of partitions confusing. If you think of the partitions as separate hard drives, this should not be a problem.

Disagreeing with Steinberg

Incidentally, in his “Mac OS 9: The Complete Reference,” Gene Steinberg suggests that having operating systems installed on more than one hard drive partition, and using the Start Up Disk control panel to select which one to boot from, is a bad idea that can cause problems. I usually agree with Gene, and I defer to his much greater variation regarding Mac operating systems then I possess, but I am obliged to part company with him on this one.

I have personally used multiple operating systems on partitioned hard drives on a variety of Macs ranging from my old Mac Plus (yes, I even partitioned the 20 MB hard drive on the Plus in order to have both System 6 and System 7 available), through a PowerBook 5300, the WallStreet, my son’s PowerBook 520, another WallStreet, and Lombard ‘Books, and my latest addition, a Umax SuperMac S900. I have never once experienced any problems that I would attribute to having the multiple systems installed on any of these machines – and the redundancy his bailed me out of several scrapes and been a great convenience many other times.

Publisher’s note: I have been doing the same thing since I had a 40 MB hard drive attached to my Mac Plus. One partition for System 6, another for System 7. Like Charles Moore, I have never encountered any problems related to partitioning, and having a bootable “emergency” partition has saved my bacon several times over my 32 years using Macs. In 2018, most of my modern Macs have a partition with Mac OS X 10.6 Snow Leopard (for some apps that require it) and another with Mac OS X 10.11 El Capitan, assuming the machine can run it. I also have a small macOS 10.13 High Sierra partition on my fastest iMac for when I receive files that need the latest version of Pages or some other app. (Apple introduced the Apple File System with macOS 10.13 High Sierra in March 2017; it is at present limited to use on SSDs.)
Once upon a time, there was something called “soft partitioning” which created virtual partitions controlled by software. This could be very troublesome but pretty much vanished from the Mac world once Apple replaced MFS (limited to 20 MB) with HFS in Sept. 1985 with System 2.1. Avoid soft partitions if at all possible – you’re only likely to see it on hard drives for the Mac 128K and 512K. Daniel Knight

Oddly enough, Apple’s own hard drive formatting software bundled with the Mac OS did not include partitioning capability until they replaced HD SC Setup with Drive Setup not long before HFS+ was introduced. However, several third-party formatting programs such as FWD’s Hard Disk Toolkit or LaCie’s Silverlining could do the job for you. Apple’s current Drive Setup formatter supports partitioning nicely – at least for Apple-branded drives. For third-party drives, you may or may not still need third-party formatting software.

Backup Before You Partition

In order to partition your hard drive, it must be erased and reformatted.*** Consequently, you will need to back up all of your files to other media before partitioning. Obviously, the ideal time to partition a hard drive is when you first get your computer.

If you are partitioning a drive that has been in use for some time, it’s probably also a good idea to do a clean system install while you’re at it. Make sure to save any third-party extensions and other non-Apple System Folder stuff before erasing your old system, although you will probably have to reinstall some of your software.

Once these preparations are complete, boot your Mac from a CD, a Disk Tools floppy, or an external drive. You can find Drive Setup in the Utilities folder of your system CD. Launch Drive Setup and choose Customize Volumes or Custom Setup from the Functions menu.

You must also select a file format method from the format popup menu. Choose HFS+ unless you want to be able to access the partition over a network or using PowerBook SCSI Disk Mode from an older computer running an operating system prior to Mac OS 8.1 that does not support the Macintosh extended file format. (68040-based Macs cannot boot from an HFS+ volume.)

You now have two options for determining the size of your partitions. One way is to use the popup menu to indicate how many partitions you would like to have. With this method, all the partitions will be automatically sized in equal proportions. However, you can also drag the rectangle borders in the setup window to change the relative size of your partitions to a variety of capacities. On my WallStreet, I have three 320 MB partitions and a fourth of a little more than a megabyte.

Once you have mapped your partition sizes to your satisfaction, click the Initialize button and Drive Setup will create your partitions. When that process is completed, you can reinstall a system or systems, as well as your applications and other files on the newly partitioned drive.

Partitioning is not for everyone, but it is one of the options that can help you customize and optimize your Mac to suit your particular needs and preferences.

 * HFS can allocate up to 65,536 allocation blocks, each composed of one or more 512-byte sectors. This means that the Mac OS will allocate drive space as efficiently as possible with partitions up to 32.75 MB in size. With partitions up to 65.5 MB, it will allocate two sectors per block, and so on. A 500 MB hard drive with four equal partitions would allocate 4 sectors per block, while a 500 MB drive with one partition would allocate 16 sectors per block. That means the smallest file would use 8 KB of hard drive space on a 500 MB drive – but only 2 KB if the drive was partitioned four ways.

 ** HFS+ can allocate up to 4.294 billion allocation blocks, each composed of one or more 512-byte sectors. This means that the Mac OS will allocate drive space as efficiently as possible with partitions up to 2.147 GB. With partitions up to 4.294 GB, it will allocate two sectors per block, and so on.

 *** This was true until Mac OS X 10.5 Leopard arrived in October 2007 with the ability to non-destructively repartition your hard drive.

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