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Partitions and Multiple Operating Systems

Hello again.  

First I want to thank everyone that wrote in about my last article on System Resources.  Hopefully I didn’t get too geeky.  As always if you have any comments about my writing please e-mail me at abcomputers@pcsleuth.com. 

This month’s topic is actually two; Partitions and Multiple Booting your computer.  Unfortunately these topics are pretty geeky (sorry), so please bear with me, hopefully by the end of the article it should make some sense.

Creating a multiple boot computer can cause data loss, so if you decide to try this make sure that you have a good back-up and test it to make sure that you can recover.  I used to work at a motorcycle shop where we had a sign on the wall that said “If you have a $10 head, wear a $10 helmet”.  Well, the same holds true for your data. If it is important to you, BACK IT UP. 

In order to understand Multiple Boot systems, you will need to understand Partitions, and Hard Drive geometry.

Geek Terms

Let’s start by defining some terms.

Partitions

A partition is a section of your drive. You may not realize it, but all hard drives have partitions.  If your hard drive has a single partition then you see that as drive C in Windows or DOS.  Partitions are created with partitioning software like fdisk for Windows or DOS.  You can use fdisk to create more than one disk on a single hard drive.  There are certain rules for Partitions:

Partition rules

• You can have no more than 4 partitions on a hard drive.  However one can be an extended partition and it can contain multiple logical drives.

• To be bootable (by DOS, Windows and some Operating Systems (OSes), partitions must be primary, active and the first sector must below the 1024 cylinder limit (8 GB).  For DOS in particular the boot code MUST reside beneath a 2GB barrier.

• DOS and Windows 9.X should have only one visible primary partition, or data corruption may occur.

Formatting

Before a partition is usable it must be formatted.  When you format a partition, a File Allocation Table (FAT) is created.  The FAT maps out the available space in the partition in to clusters so that when you write data to the hard drive it can found again.

Cylinders

Hard Drives are constructed out of platters; the platters are round and look like a stack of pancakes with a little gap in between them.  We define the size of a hard drive in Cylinders, Heads and Sectors.  A track is the section of a platter that can be read with out moving the head.  When we look at all the heads, a cylinder is a collection of all the tracks on the platters that can be read with out moving the heads.

It may help you to think of Cylinders like this:  Take our stack of pancakes (platters) from above and cut a circle out of the middle of them.  Now cut a ring off the outside.  If you remove the inner circle and the outer ring from the stack, what remains is a cylinder with each pancake ring being a track.

Sectors

Sectors are a subdivision of tracks.  They are smallest size unit that can be written to a hard drive.

Clusters

Clusters are created by formatting a partition, they are sized by the OS and the type of FAT used.  Clusters are a collection of sectors on the hard drive.  Each cluster can only contain one file or portion of a file.  Each cluster is represented by an entry in the FAT. The size of each cluster is determined by the OS and type of FAT.

Multiple boot

Multiple Boot refers to computer that can boot to more than one OS, for example my main desktop computer can boot in to Windows 98, Windows XP, Windows 2000 Pro, Linux Mandrake 8.0 and BEOS 5.  In a multiple boot scenario you normally choose the OS to boot when you turn on your computer.

Why you may want to have a multiple boot computer

Run More than one Operating System

A multiple boot computer is great way to try out an OS with out having to make a long term commitment to a new OS.  For example one of the reasons I multiple boot my computer is to give me the ability to try out the beta versions of Windows XP.  Using a multiple booting system I can try out a beta OS on my main desktop safely, without putting my important data at risk. 

Some other OSes you might want to try.

• Other versions of Windows ie: Windows 9.5, 98, NT 4.0, XP

• DOS

• BEOS

• Linux

• Unix

Caveats

There several things you need to know before you create a multiple boot computer.

1024 cylinder limit

Several OS have a requirement that either all or some their bootable partition reside below the 1024 cylinder barrier.  The 1024 cylinder barrier equates to 8 GB.  OSes of this type include all versions of Windows.

Primary partitions

Most OSes must reside on a Primary Active Partition to be bootable.

Tools

Partitioning Tools

Before I talk about some specific partition managers, I have to warn you that playing around with the partition table of your hard drive, may cause you to lose everything on your hard drive.  So if your data is important, BACK IT UP. 

Partition Managers are software utilities that are used to manage your partitions.  Before you try and create a multiple boot system, create a bootable diskette that will give you access to your partitioning tool. Make sure that you TEST IT!

Fdisk

Fdisk is a command line based partitioning tool that is included with DOS and Windows, there are also versions of fdisk included with many Linux distributions.  Fdisk, while very functional is a very bare bones utility, it often can’t recognize partitions that were created by a different partitioning tool, also repartitioning your hard drive with fdisk WILL ERASE your data.

Partition Magic

Partition Magic is GUI based partition manager that allows you create, resize, copy and move partitions.  It also allows you to convert partitions between different formats.  In most cases you can do all of these things with out loosing any data.  You have to buy Partition Magic.  In my opinion Partition Magic is the best bet of all partitioning tools.  It also includes the boot manager Boot Magic.

Ranish Partition Manager

Ranish Partition Manager is a free utility to help you manage your partitions. It allows you to; Save and restore MBR, Create and delete partitions, View hard disks' IDE information, Format and resize FAT-16 and FAT-32 file systems.  It includes Advance Boot Manager.

Partition Commander

Partition Commander is GUI based partition manager that allows you to create, resize copy and move partitions.  Like Partition Magic you have to buy Partition Commander, it also includes the boot manager System Commander.

Boot Managers

Boot Managers are software that provide an easy way to choose which operating system you want to run.  They can often hide unused primary partition(s) and set a partition as Active.

Windows NT

The boot manager included with Windows NT, 2000 or XP is a very powerful tool but can be tricky to configure. It must be booted from a partition inside the 1024 cylinder limit.

System Commander

System Commander is my favorite boot manager, it has features that the others don’t and is fairly straight forward to configure.  You have to purchase System Commander.

Boot Magic

It is the boot manager included with Partition Magic.  Boot Magic is very easy to use, but isn’t as configurable as System Commander.

Advanced Boot Manager

Advanced Boot Manager is included with the free program Ranish Partition Manager. 

Lilo

Lilo is the LInux LOader.  It can be used to load other OSes as well.  It can tricky to configure properly.

How to create a multiple boot computer

There are a number of ways to create a multiple boot computer, I will cover 2 common scenarios, but they can be expanded and combined to create the others.

Scenarios

One Primary Partition

It is possible to create multiple boot computers with only one primary partition.  That partition must contain your boot manager.  Since almost all OS can read a write to FAT16 your primary partition is usually FAT and therefore limited to 2 gigabytes in size. 

You can do this having one primary partition and at least one other partition (which can be on another drive).  What you do is load Windows 9.x or DOS on your primary partition then insert the set-up disk for a Windows NT  based OS (NT, 2000, XP) and run set-up but have it install the NT based OS to a partition other than C:.

The limitation to this method is if you want to remove one OS, You will still be booting to FAT partition, If that partition does not contain an OS it may get confusing.  For example in DOS/Windows nomenclature, your autoexec.bat will be on drive C: while Windows is located on drive D:\.  It must be noted that Microsoft no longer supports more than one OS on a single partition. 

You need to be careful in this scenario, some programs default to installing to c:\Program Files, so if you remove the Windows 9.X OS you will lose access to those programs from the other OS.

Multiple Primary Partitions

This is my preferred method of running more than one OS on a system.  What I do is create 3 primary partitions on a hard drive, with each partition having a presence below the 1024 cylinder limit. The advantages to this method are:

Each OS is completely hidden form the other OSes on the computer

I can use a logical drive on an extended partition as a programs drive that can hold programs that are accessible to other OSes.

I use my partitioning tool to unhide the first primary partition and set it as active and hide the other 2 primary partitions. I then install the oldest OS on the first primary partition; along with my Boot Manager (I keep the first partition’s size below 2 GB if it will contain DOS or Windows 95 original). 

I then use my partitioning tool to hide the first primary partition and set the second primary partition as active.  Now I load the second OS.  I usually make this Partition just under 6 GB.

I again use my partitioning tool to hide the First and second Primary Partitions and unhide the third primary and set it active.  Remember that the third primary partition MUST have enough of it existing (large enough section to contain the boot files) below the 1024 cylinder limit in order to be bootable for most OSes.  Now I load my third OS.

After loading the three primary OSes, I use my partitioning tool again to hide the third primary partition and set the first primary partition as active and unhidden.  I boot to the first OSes and reload my boot manager and configure it to boot to my 3 OSes.

Now I load my programs under the appropriate OSes on to drive D:.  Remember that each program you wish to use with an operating system must installed under that Operating system.  You can however install to the same drive and directory to save space. 

Recommendations

I prefer the Multiple Primary Partition method for multiple booting my systems.  I find that if one OS goes down, I don’t lose my other OSes and therefore I can still use my computer.  My favorite partition manager is Partition Magic; I find it safe and easy to use.  My favorite boot manager is System Commander; I find to be the most powerful, it makes it easy to boot from more than one hard drive.

I know this topic was very geeky.  Hopefully it helped you understand some the issues surrounding multiple booting your computer.  I know that it got fairly deep, but that is what the topic required.  Unfortunately creating a multiple boot computer is not a trivial undertaking.  I recommend that you read the documentation for any OS you wish to use, and for the tools that you choose before you start.  Please back-up your data before you start, it is very easy to make a mistake and lose everything on your hard drive.

As always please let me know if you find this article too hard or not in-depth enough.

See you next month!

Hal Cardona
PC Sleuth

Hal Cardona, PC Sleuth, serves as tech support and/or offsite Sys Admin for over 200 clients around the US.  He designs, builds, and troubleshoots networks and builds custom computer systems.