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Partitioning - Part 1

Toronto Star Fast Forward column for Feb 12/98

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© Copyright, Myles White, 1998

Today's Computer Wares isn't really in the Back to Basics series, but it comes close. It's actually a review of a software product used as an excuse to provide some lead-in background to go with next week's reader letter Q&A column in which I'm going to talk about Quarterdeck's new Partition-It Extra Strength utility later, but first, I want to help you understand why PC users may need it, and applications similar to it, and why Mac users may wish they had a similar tool.

Over the past few years, partially because of technological improvements, partially because the prices have plummeted and partially because today's software demands so much space to install, hard drive capacities have increased tremendously. Hard drives (also known as hard disks, fixed disks or, if you work for IBM, as hard files) are necessary because the days when a program could be run from a single floppy disk are well and truly long behind us. Hard drives are where you store the computer's operating system and the applications you run, as well as the documents or other data you produce when you use them.

It doesn't take a whole lot of work to find ads for even low-end systems with hard drive capacities of 1.6 gigabytes (GB -- 1024 megabytes or MB). At the higher end, systems with hard drives capable of holding over 9 GB are no longer uncommon.

Unfortunately, with this increase in capacity, it's only recently that both PC and Mac operating systems have caught up and what we've gained on one hand (more storage space), we've curiously lost on another (less space than you think).

Those of you who become drowsy when numbers appear in computer columns may want to get a coffee before reading this next bit. Unfortunately, a little math is unavoidable to have this make sense.

It's in the numbers

If you've spent more than a couple of minutes looking at ads or computer documentation of any kind, you'll have noticed that some numbers appear with great regularity. Numbers such as 128, 256, 512, and 1024 are everywhere and, particularly when talking about video, bigger values such as 65,536 and 16.7 million show up a lot. They're common because binary math, the kind you use when talking about computers, that nasty stuff comprised of only two values, one or zero (1 or 0), always translates into factors of 2. One binary digit (or bit) has a maximum value of 2 and as you add bits, you don't add 2 to 2, you multiply.

If you've managed to get this far, the rest is easy. Ever wondered why certain limits are placed on things you can do in computers? For example, the character sets used in both PCs and Macs can have only 256 different symbols. The reason is that each character you see on screen is described using 8 bits of data and the maximum base-10 (or decimal) value that can be formed with 8 bits is 256 (2<superscript>8<superscript>). Another place where 256 is commonly used is to describe the number of shades of grey you can see in a scanned black and white photograph. Why? Only 8 bits of data are commonly assigned to determine the number of shades you can see. How about a more common (albeit newer) limit that says file names can be up to, but not exceed, 256 characters in length? Same limit and same reason - the part of the operating system that handles file names is calculated based on the 8-bit character set.

Now we come to another limit. In early PCs and Macs, primitive spreadsheets and databases often ran into problems because they could only display 65,536 cells (65,535 if you started counting at 1 instead of 0) or 65,535 records, or in some cases that were truly bizarre, could only calculate numbers up to, but not exceeding 65,535. Why? They were based on 16-bit values (2<suprscript>16<superscript>).

And that brings us back to hard drives, finally.

On files and fat

Prior to Windows 95B (also known as Original Equipment Manufacturer Service Release 2 or OEM Service Release 2 or finally, OSR/2) and the new Macintosh Operating System (MacOS) version 8.1, the part of the operating system that kept track of where files were on a hard drive was based on a 16-bit table. In PCs, the File Allocation Table or FAT had a limit of 65,536 values it could assign to any drive partition and Mac users faced a similar limit.

Partition? Oops, here we go again. Imagine your hard drive is similar to an apartment building. Now imagine the building is just a shell without floors. You've got lots of space, but without a suitable place to put things, they all just pile up. If we were talking about a really small disk (like a floppy), the analogy still holds, only now we're talking about a toolshed, instead.

It makes sense to divide the building into smaller areas by using floors. On a really large hard drive, it makes just as much sense to install partitions. In the building, you now have a basement, ground floor, second floor and so on. In your hard drive, instead of having drive C:\, you now have drives C:\, D:\, E:\. and so it goes.

Back to the FAT. Let's stay with the apartment analogy. In our building, each floor is divided into spaces called apartments (or suites if you live in a ritzy place). The smallest division a PC operating system can create in a hard drive partition is called a cluster.

In the apartment building, there is a list of tenants at the door. On your hard drive, there is the file allocation table (FAT) that tells the operating system where a file starts, where its parts are located and where it ends.

The maximum number of apartments in the building is determined by its size and local zoning regulations. The maximum number of entries in the FAT is determined by the number of bits used by the operating system to number them.

In the apartment building, it doesn't matter how big or how small each apartment is, it is considered rented and occupied whether there is one person or a whole clan living in it. On your hard drive, it doesn't matter how big or how small each cluster is. Whether it's full or there is only one bit of data in it, then it, too is considered occupied.

Using a 16-bit file system, it doesn't matter how large (or small) each partition is on your hard drive; the maximum number of divisions is 65,536 (numbered 0 through 65,535). If the partition size goes up, but the number of divisions can't increase, the only other option is to increase the size of each one.

In a PC system with a 16-bit file scheme, a hard drive with a 1 GB partition uses 16 KB clusters. In a 2 GB partition, the number increases to 32 KB and to 64 KB after that -- and it doesn't matter if there's 32 KB or 64 KB in the cluster or 1 bit; you still lose all the space if even part of a cluster is used. Every file, no matter how small it is, uses at the very least the amount of space allocated to one cluster.

In a Mac system it can get worse. Using the Macintosh Standard Format (hierarchical file system or HFS) and because the Mac uses a scheme known as forking, a file with 1 bit in it, if it has two forks, could occupy as much as 128 KB of space in a hard drive with a partition larger than 2 GB.

What's it mean to you? Figures supplied by Quarterdeck will help here. Using Microsoft Office 95 as an example, the amount of space it needs for installation on a PC hard drive with a 2 GB partition (32 KB clusters) is 120.28 MB. On a 1 GB partition (16 KB clusters), it's 109.45 MB. On a 512 MB partition (8 KB clusters), it's 104.23 MB. On a 256 MB partition (4 KB clusters), it's 102.02 MB, and so on.

That's a lot of lost space. In the difference between 32 KB clusters in a 2 GB partition and the 4 KB clusters in a 256 MB partition, we're looking at nearly 20 MB literally "lost in space." Given the mix of file types and sizes on a typical hard drive, you'll typically lose hundreds of megabytes to dead space on a large partition.

The solutions

If you're a PC user, one solution is to wait for Windows 98. It will allow you to convert your hard drives to a new 32-bit file table (known as FAT32). Because the 32 bits of data now allow for up to 4.2 billion divisions, cluster size is reduced to 4 KB for partitions up to 8.4 GB. MacOS 8.1 also uses a new 32-bit file block allocation scheme. It was temporarily known as "HFS plus," but more recently is simply referred to as Macintosh Extended Format.

The second solution for PC users is to back up all software applications and data from an existing large hard drive (all partitions), then use the operating system utility, FDISK to re-partition the drive into smaller sections. If you do this, all data on the drive will disappear; the drive partitions will need re-formatting, and you'll have to reinstall Windows 95, as well as many of the applications (because the Windows Registry will be trashed, too). Ugh.

The other solution is to use partitioning software, instead and we'll talk about that next week. I also want to thank two new friends who have volunteered to act as my Mac advisors. I'll tell you more about Steve Patterson and John Nicholls next week.

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