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A Swiss reader, Thierry Piolino, wrote last week:

I keep reading that people have their HDD partitioned. Can you please give me a hint how I could do the same thing on my 20GB HDD (as I understand, I have to boot from another drive and can only have a blank disk partitioned).

Thanks for your help and kind regards.
T. Piolino

By coincidence, I already had a draft for the following Mac basics article roughed out when I received Thierry's email.

A Mac user could go forever without partitioning his or her hard drive and be perfectly happy, and probably most do -- even many power-users.

Back in the old days, before Mac OS 8.1, there was a particularly compelling reason for partitioning one's hard drive into two or more virtual volumes. Under the old, Mac OS Standard (HFS) disk formatting protocol, a volume, no matter what its capacity was, would be subdivided into a maximum of 65,536 "blocks" of data.

This was no problem on a floppy disk or on the old, small hard drives of 20, 80, or at most a few hundred MB capacity. However, it could waste hard drive space, simce even the smallest file --say a couple of sentences of text -- would occupy an entire block, and as the drive capacity increased, the blocks just got bigger, wasting even more space. Even a 10k text file on, say, a 4 gigabyte drive, will occupy 65 K, the smallest block size under HFS formatting on that size drive.

The workaround was to partition the drive, since the smaller multiple volumes would naturally have smaller block sizes. For example, when I created four partitions on my PowerBook 5300's 500 MB hard drive, and restored the same collection of files, I found that I had magically gained about 35 MB of free space.

However, as hard disk capacities grew to 1 GB and beyond, the block sizes with HFS formatting became simply ridiculous, so starting with OS 8.1, Apple introduced the Mac OS Extended Format -- HFS+ -- which increased the maximum number of formatting blocks on a drive to 4.29 billion, making each block minuscule compared with HFS formatting.

HFS plus consequently removed one of the main reasons for drive partitioning, so is there any advantage to for partitioning today? I think so.

Hard drives nowadays are humongous compared with even a few years ago. My Mac Plus ran on 800 K floppies or an external 20 MB hard drive. My LC 520 came with a 160 MB drive, the PowerBook 5300 a 500 MB unit, and my WallStreet G3 PowerBook came with a 2 GB drive. My Cube and Pismo PowerBook shipped with 20 GB hard drives, and you can get a 48 GB drive with the newest TiBooks.

I find that having any drive, but especially the big ones, partitioned into smaller volumes, is helpful for organizing things better. I have settled on four partitions as being ideal for me. I use the top level partition for my working system and its associated files. The second partition is for applications; the third one is for document archives; and the fourth is a general dumping ground for everything else -- mostly software installers or anything really big. Works for me. Having the files on my hard drive organized this way also speeds up Sherlock searches, because you can specify just one volume to be searched.

However, one of the biggest advantages of doing this is that it allows me to keep several system versions installed on my hard drive, and select which one I want to start up with in the Startup Disk control panel, which can be very convenient. On my WallStreet, I have OS 9.0; 0S 9.1; and OS 9.2.1 installed (I also have SuSE Linux 7.1 installed on yet another, AUX partition, but that's another movie). I find this multiple systems approach very useful for troubleshooting system problems. It also enables me to install a new system, most recently OS 9.2.1, without disturbing my existing working system. In the latter case I was very glad that I did, because I did not like OS 9.2.1's propensity to lock on waking from sleep.

I even partitioned to little 20 MB hard drive on the old Mac Plus so that I could keep System 7.0 for Internet access, and System 6.0.8 for speed.

Partitioning can also be convenient for Macs that are used by more than one individual -- everyone can have their own personal volume with files, applications, and System preferences set up the way they like (provided they install a system on that volume.

The best time to partition a hard drive is when you first get the Mac. That's because you must erase the drive's directory in order to format the partitions, which means backing all of your files up to another volume(s), which is time consuming if you have a lot of files and applications.

On a new Mac, or after your files are safely back up (in two places for really important stuff) partitioning is very easy to do using the Drive Setup utility that ships with every new Mac operating system. Version 7.3.5 and later of the earlier HD SC Setup utility will also format SCSI drives on older Macs with partitions.

Boot your Mac from another volume such as the system restore CD or a system installed on a Zip Drive or FireWire Drive, and start up Drive Setup, which can be found in the Mac OS Utilities Folder inside the Applications (Mac OS 9) older on your CD or boot disk. When Drive Setup starts up you will see a List Of Drives window which should show your Mac's hard drive, and whatever disk you have used to boot from.

Select the Mac Hard Drive or whatever your hard drive is named and click Initialize, which will erase all of the file directory information from your hard drive; then choose Customize Volumes from the Function menu. The Custom Setup window will appear.

Use the pulldown menu in the window to specify how many partitions you want to have (a partition map of your subdivided drive which will appear in the Volumes box with the appropriate number of dividers, which can be dragged up or down to configure the relative size of each volume).

Specify the type of formatting you want (usually HFS+) in the pulldown menu in the Volume Info box.

Once the partitions are configured to your satisfaction, click OK and quit Drive Setup. You will see that you now have two or more hard drive icons (plus your boot volume) visible on your desktop.

Now you will have to reinstall a system on at least one of the new partitions in order to boot from the hard drive. Restore your application and document archive files, and you're done.

Selecting Drive Setup Help from the Help menu will assist you in making the steps required to partition your drive, if you're still unclear on any points.