Ignorance is bliss. Unfortunately, bliss using personal computers amounts to little short of an oxymoron. Some people can remain rather ignorant about their PC and still muddle along OK. Those people generally don't actually accomplish much with their PC. For the rest, getting good use from their PC requires shedding some ignorance. Many who have progressed to this stage find that some things they wish to do with a PC are more difficult or even impossible to do with the operating system on their PC. It is to those people who have chosen some form of OS/2 to be one of two or more operating systems to run on their PC that this page is primarily addressed, but it applies generally to any PC OS, particularly Linux.
This page is not intended to persuade anyone that any particular combinations of operating systems are good or bad, and neither that any particular operating system is good or bad. It is here merely to educate on various issues impacting installing and running OS/2 in conjuction with one or more other operating systems on the same PC, what is defined as multiboot.
Multiboot is a complex subject. Creating a smoothly operating multiboot system is arguably as much an art as it is a science. Many issues affect choices to be made. Thus, there can be no single "right" way to proceed to a successful end.
Of particular concern here is the initial phase of getting multiple operating systems operational: choosing how to allocate storage space, both current and planned expansion; allocating the space; and then getting through the operating system install processes without damaging coexisting operating system installation(s).
Dual boot is the simultaneous presence of two bootable operating systems living and/or starting up from the same partition. You can install DOS on C:, then install an older OS/2 version or a version of Windows® or a Linux loader on C:, and switch between the two using the boot command or a startup menu. Modern OS/2 versions have discontinued support for dual boot.
Multiboot is the simultaneous presence ot multiple bootable partitions in the same system, such as DOS on one partition, OS/2 on another partition, and Linux on yet another partition. These bootable partitions all can reside on the same physical disk, or on two or more physical disks. In order to choose which operating system to boot, a boot manager is usually necessary.
The term "dual boot" is often used when multiboot is actually meant. Dual means two exactly, while multi means more than one. So, the two terms can easily be confused when the actual count is two.
AFAIK, IBM first made the distinction back before Torvalds' kernel was first used for GPL operating systems, sometime around 1987 I think, certainly by 1990. OS/2 at the time was capable of being installed both as dual boot and as multiboot on the same system, and some linguistic distinction between the two was required in the documentation.
Various solutions exist for running non-native software in a host operating system. Wine permits most Windows® software to run under Linux. Odin permits most older Windows® software to run under OS/2. Various applications permit Windows® software to be run on a Mac. Parallels, VMWare, VirtualBox, Microsoft Virtual PC and others permit an entire operating system and its native software to be installed as an application under a host OS.
KVM switches permit sharing keyboard, mouse and display among one or more computers, and there are a lot of perfectly usable old computers around not being used. Many companies that periodically upgrade have trouble finding ways to get rid of old systems without sending them to landfills.
A partition is a logical (software) subdivision of a whole physical device that is treated by an operating system as if it were a whole physical device.
This is a 64 byte data structure containing up to four 16 byte units defining the status, type, location, and size of partitions. Only the partition table in the master boot record contains entries defining primary partitions.
It is found in bytes 1-64 of the last 66 bytes of each partition boot record, including the master boot record.
This is executable code located in the first logical hard disk sector, which is designed to find and transfer control to a startable partition. The PC BIOS looks for this code to transfer control to when the POST is complete, according to the settings in the BIOS regarding boot device order.
Without any partitions, the MBR code has no place to transfer control to cause a hard disk boot, resulting in a boot error message like "operating system missing" or "operating system not found". Multiple partitions are typically used to segregate data used for different purposes, such as operating systems, applications, and data, or different operating systems. Not all operating systems can access all types of partition formats, so different partitions may be required to segregate the various formats required by the operating systems in use.
In order to use a hard disk, there must be at least one. In most cases, each operating system either requires, or should be installed to, its own separate partition. Beyond that, it depends on your needs. The fewer partitions you have, the greater the potential for loss in the event of file system corruption. The more partitions you have, the smaller each is, which can make backing up and managing backups easier. On the other hand, the more partitions you have, the more difficult it can be to find something you are looking for, or to decide where to save something.
This depends on the operating system or systems you use and the tools used to partition. Some versions of some Linux partitioning tools will refuse to create more than 15, even though Linux can traditionally recognize up to 63 per PATA disk. In most versions of the Linux kernels released since 2006, the default libata drivers used for PATA disks limit them to 15 partitions per physical device. As of mid-2007, at least one userspace solution that permits access to up to 63 partitions per PATA or SATA disk has been in development.
For operating systems that assign drive letters to partitions, the practical limit is the amount of letters in the ASCII alphabet, less A, B, and however many are required for other removable media devices, usually 23 at most, plus however many that don't need letters but are used for other operating systems.
This varies according to hardware, OS and partition type. One of the lowest limits is the FAT16B used by legacy DOS, limited to to 65536 clusters of 32768 bytes (64 * 512 byte sectors), totalling 2,147,155,968 bytes, or about 2 GiB. HPFS is much better with a 64 GiB limit. Newer filesystem types can have sizes measured in TiB.
Big enough to hold what it needs to hold. Things to considering in choosing a size include, but are not limited to:
Each operating system provides one or more tools for the purpose. DOS, Windows®, OS/2, and Linux all do or did provide a tool named FDISK. Linux distros provide others in addition to fdisk, such as cfdisk, sfdisk, parted, and RedHat's Disk Druid. MCP, WSeB and eCS provide LVM. All these tools' purpose is primarily that of partition space allocation, but each can also set a primary partition active, and the Linux versions can perform additional functions.
The legacy of the various partitioning tools provided with operating systems is to presume that no other operating system is or will be concurrently installed. The result of this is that occasionally such a tool will take some action that damages or even destroys the possibility of another partition successfully booting or being accessed by the other operating system. Recent versions of some of these tools have improved, but the safer alternative on multiboot systems is typically to use an independently sourced and platform agnostic partitioning tool.
Using an independent tool prior to operating system installation helps avoid unwanted surprises. An example of what might happen if you don't follows:
|/dev/hda1 - Linux ext2 100 MiB
/dev/hda2 - Win fat32 10 GiB
/dev/hda4 - Extended
/dev/hda5 - Linux swap 258 MiB
/dev/hda6 - Linux ext2 3 GiB
/dev/hda7 - Win fat32 9 GiB
/dev/hda8 - Linux ext2 2.5 GiB
blank (freespace) 5 GiB
/dev/hda1 - Linux ext2 100 MiB
/dev/hda2 - Win fat32 5 GiB
/dev/hda4 - Extended
/dev/hda5 - Linux ext2 5 GiB
/dev/hda6 - Linux swap 258 MiB
/dev/hda7 - Linux ext2 3 GiB
/dev/hda8 - Win fat32 9 GiB
/dev/hda9 - Linux ext2 2.5 GiB
/dev/hda10 - Linux swap 258 MiB
/dev/hda11 - Linux ext2 4.7 GiB
/dev/hda1 - Linux ext2 100 MiB
/dev/hda2 - Win fat32 5 GiB
/dev/hda3 - Linux ext2 5 GiB
/dev/hda4 - Extended
/dev/hda5 - Linux swap 258 MiB
/dev/hda6 - Linux ext2 3 GiB
/dev/hda7 - Win fat32 9 GiB
/dev/hda8 - Linux ext2 2.5 GiB
/dev/hda9 - Linux ext2 5 GiB
Initially, there were two fully functional operating systems installed, using multiple partitions each. After installing a second instance of Linux, and having its installer split /dev/hda2 into two, those originally contained in the extended were all shifted up by one number, rendering the original installation unbootable without repair. By using another tool before installing the second Linux, one could have the instead version, creating an additional primary instead of shifting the extended logicals, and with the added benefit of not creating an unnecessary swap partition on the same disk.
Other tools available independently from any specific OS include DFSee, PartEd, Parted Magic and Partition Magic. Independent tools may provide services other than mere space allocation, such as partition hiding & unhiding, moving, cloning, or formatting.
Some tools, such as Partition Magic, can do this as a one step process. Other tools, such as older DFSee versions, can do this in a multistep process, by first cloning, then removing the original.
It is not always posssible to move a partition to a particular desired location without moving something else first. Moving a partition is generally considered risky, and so should not be done without careful consideration to the risk involved, and backups commensurate with that risk.
To be compatible for use by DOS, OS/2 and Windows®, all (note) partitions on a hard disk must begin on the first logical sector of a logical disk cylinder. Therefore, compatible partitions are always multiples of a logical disk cylinder. With modern large disks, the minimum cylinder size is 16065 logical sectors, approximately 7.84 MiB, and larger partitions are multiples of this size. Some versions of Linux partitioning tools can create partitions that do not begin on cylinder boundaries, but disks so partitioned will not be usable except by Linux.
Note - Technically, most partitions begin on the first logical sector on the second logical track of a cylinder. The exceptions are primary partitions other than a primary that begins at the very start of a disk, which do start on the first sector of the cylinder.
The prefixes milli (10-3), centi (10-2), deci (10-1), kilo (103), mega(106), giga (109), tera (1012), etc. are metric SI unit multipliers. This decimal system is how humans do math. It is the system used by the hard drive makers, whereby 80 gigabytes means 80,000,000,000 bytes.
Computers do their math in binary, powers of two. Early on the computer industry hijacked the decimal prefixes for use with their non-decimal numbers. When a drive maker's 80 gigabyte drive is sized by a PC, it comes out to about 74.5 binary "gigabytes". 80 binary "gigabytes" is 85,899,345,950 bytes.
The IEEE Standards Coordinating Committee 14 has proposed a standard to deal with the discrepancies this hijacking created. You can find a more detailed explanation of this proposed resolution at Proposed IEEE 1541: The Compendium of Prefixes for Binary Multiples and also at NIST's Prefixes for Binary Multiples.
Every extended partition contains a partition table. This partition table must occupy bytes 1-64 of the last 66 bytes of the first logical sector of a logical cylinder. Since the master boot record occupies the first logical sector on a disk, an extended partition cannot begin there, and the remainder ot that cylinder is always unused, unless a primary partition begins there.
Primary partitions are defined at the end of the first logical sector on a disk, while logical partitions are not. The location of the first logical partition definition is stored in one of the primary partitions, called an extended partition. Any additional logical partition is defined in the location specified along with the current logical definition. All are chained into one logical partition table for purposes of defining the overall partition layout.
Whether a partition is logical or primary can affect drive letter assignments, and whether a bootloader can successfully boot a particular operating system or partition. Otherwise, there is no reason to differentiate between them. Once an operating system is booted, there is no functional difference.
Until the advent of Windows® NT's LDM and OS/2's LVM, this was the responsibility of the kernel and the storage access drivers. An OS/2 LVM-enabled system has the logical volume manager assign drive letters according to the whim of the user. Such drive assignments survive boots, that is, they stick, or remain unchanged from boot to boot, because LVM writes the information to disk, and the storage access system uses this saved information during OS startup.
Letters are assigned anew at each boot by DOS, Win9x, and non-LVM-enabled OS/2. The order is alphabetical consecutive beginning with C:, which is assigned to the first visible partition found by the MBR boot code in the following order:
Visible primary on 1st BIOS drive
Visible primary on 2nd BIOS drive
Visible primary on 3rd BIOS drive
. . .
Visible primary on nth BIOS drive
1st visible logical on 1st BIOS drive
2nd visible logical on 1st BIOS drive
3rd visible logical on 1st BIOS drive
. . .
nth visible logical on 1st BIOS drive
1st visible logical on 2nd BIOS drive
2nd visible logical on 2nd BIOS drive
3rd visible logical on 2nd BIOS drive
. . .
nth visible logical on 2nd BIOS drive
1st visible logical on 3rd BIOS drive
2nd visible logical on 3rd BIOS drive
3rd visible logical on 3rd BIOS drive
. . .
nth visible logical on 3rd BIOS drive
1st visible logical on xth BIOS drive
2nd visible logical on xth BIOS drive
3rd visible logical on xth BIOS drive
. . .
nth visible logical on xth BIOS drive
removable media drives
CD and DVD drives
On legacy systems, such as DOS, Win9x and Warp, this can only be done by hiding, unhiding, creating, and/or adding partitions or partitioned disks that cause existing letters to shift. On newer systems, in addition to the above methods, this can be done with a logical volume management tool, such as LVM on MCP, WSeB & eCS.
As explained in how do drive letters get assigned?, letters on non-LVM systems are assigned anew on every boot in a fixed order. Letters are said to shift when a partition is hidden or removed which previously had a lower letter assignment than the partitions remaining, which causes those remaining partitions each to take a lower letter than previously; or, a partition is unhidden or added, which due to its location other than last, takes a letter that had previously been used by a partition which remains, consequently taking a higher letter.
Problems from letter shift arise on multiboot systems because of installing an operating system or systems on either logical partitions or second disks. OS boot installations depend for every boot on retaining the same letter as assigned during install. Their configuration and ini files have the boot drive letter incorporated and will not permit successful startup when the expected drive letter is not the actually assigned drive letter.
For legacy systems, avoiding drive letter changes requires understanding of how drive letters get assigned, and proper planning accordingly.
In the simplest case, the system has only one disk to begin with, usually with two or more partitions if the system is multiboot. Since primary partitions are assigned letters before logical partitions, the easiest solution is often simply not creating a visible primary partition on the new disk.
More complicated situations abound. Sometimes keeping all the original letters isn't practical, and reinstalling using new letters is required. Sometimes adding a disk is planned for originally, and placeholder partition(s) can be used to reserve letters until the disk and its new partition(s) are added.
In most cases, yes. Traditionally, hiding a partition involves changing the type byte in its partition table entry to a value unrecognized by the operating systems involved. By convention, DOS, OS/2 and Windows® partition type bytes have their bit 4 set to hide and unset to unhide. The result of the bit 4 change is that the first ASCII character of the type byte is changed between "1" when set and "0" when unset. For example, an unhidden FAT16B partition is type 06h, 00000110b, while a hidden FAT16B partition is type 16h, 00010110b.
In newer OS versions, hiding a partition is done by using the logical volume management tool to remove the drive letter assignment.
The original PC BIOS contained data space for managing a maximum of 1024 cylinders, 255 heads, and 63 sectors per hard disk. Operating systems and storage device drivers originally depended on the BIOS for disk access. When technology produced disks larger than this data space could accomodate, old BIOS, drivers and operating systems were unable to cope, which lead to various errors or inability to access disk portions or even entire disks.
If applies with disks larger than about 7.8 MiB, 1024 logical cylinders. Usually it happens after running Partition Magic or Windows'® FDISK. Before, OS/2 worked just fine. After, something is missing from your Boot Manager menu, and you can't start up OS/2. Or, you get OS/2 started, but one or more partitions and/or logical volumes are missing. If you fix it so OS/2 and Boot Manager work right, then Windows® can't access all your partitions properly, and SCANDISK complains or refuses to complete.
What happened is FDISK or PM changed your extended partition from type 05h, the traditional type for extended partitions, the only one understood by OS/2, to type 0Fh, which Windows® requires for proper function with large disks. Windows'® 9x and ME FDISK call this "enable large drive support" when it is started. You could use any of several utilities to change the type back to the standard 05h and get OS/2 and BM to work again, but then you'd have to change it back to get Windows® to work right again.
This was a serious problem for multibooters for a very long time. Some would use utilities to switch the type back and forth. Some would just let Windows® complain. Some would add one or more extra disks and confine certain types to certain disks. Some would use alternative boot managers and/or special OS/2 device drivers to reduce but not eliminate the problem.
Finally after seven years, IBM recognized this problem needed a real solution, and released a fix, which it calls Extended Partition Support. If you have the problem, you need this fix. It works, but with a caveat. More than likely, along with the installation of this fix, you will need to replace IBM1S506.ADD with DaniS506.ADD. Without it, you are likely to be troubled with inaccessible partitions and/or drive letter shift.
The problem is best solved by proper partition planning and/or an upgrade to an LVM-enabled OS version, but sometimes things don't go according to plan, or circumstances change. Placeholder/dummy/proxy partitions can sometimes be used. A maintnenance boot may allow you to fix whatever is wrong.
Placeholder, dummy, and proxy are interchangable terms used to describe a partition created in order to cause a desired letter shift. A letter shift is sometimes desired when a system is first configured with fewer than the ultimate number of hard disks and partitions expected, and removed or hidden after additional are added.
Another situation where they are useful is when Warp 3 or 4 is installed to a logical drive on a system using FAT32 for a Windows® partition. Only later versions of IBM Boot Manager will cause a letter to be reserved for the FAT32 partition, but one cannot be installed in conjuction with the appropriate OS drivers that match the letter assignments until after the initial installation is complete, since the original Warp 3 and 4 installers will ignore FAT32 partitions. A dummy partition can bridge that gap during initial install, and be removed or hidden afterward.
These single cylinder partitions are created in front of a partition which is desired to have a higher letter assignment than it would get in the absence of the placeholder.
There are two basic reasons why this happens. First: during initial installation or installation of additional or replacement storage devices, defective, incompatible, or incorrect drivers may be installed, or drivers may be installed in the wrong loading order in CONFIG.SYS. In this situation, "OS/2 is unable to operate your hard disk or diskette drive." precedes the message. Second: system reconfiguration has occurred since the previous boot, such as adding an additional hard disk, or creating new partitions. In this situation, "The system cannot find the file F:\OS2\SYSTEM\COUNTRY.SYS specified in the COUNTRY statement on line X of the CONFIG.SYS file. Line X is ignored." precedes the message. Incorrect driver load order is also a possible cause for this message.
In both cases, boot was unable to proceed beyond IPL. In the former case, the basic storage drivers, loaded by BASEDEV= statements in CONFIG.SYS, were defective, incompatible, or wrongly selected, or loaded in incorrect sequence, resulting in failure to control your hard disk at all. In the latter case, the basedev's loaded successfully, but the configuration change following the previous boot caused the boot process to assign drive letters differently from those assigned when the operating system was installed or otherwise properly configured. This incorrect assignment is commonly referred to as drive letter shift, which causes the boot loader to look on the wrong drive for files to load and halt boot when it can't find what it needs to proceed.
Drive letters are a legacy limitation carried over from the days before hard disks, when the usual limit on drives was at most four floppies. Linux is more sophisticated than to encumber itself with artificial limitations. It can use as many partitions as required to get the job done. It "mounts" each partition it requires access to to a directory, and can do it after boot if desired, unlike legacy systems that use letters for drive access. The Linux mounting system allows for less downtime, since reboot is not required to add or remove access to a disk or partition other than root.
LVM is an acronym for "logical volume manager", which under OS/2 has two related but independent meanings. The first refers to LVM.EXE, the file executed to install and manage IBM Boot Manager, create physical partitions, and assign logical volume letters to physical partitions.
The second meaning refers to the enabling of OS/2 the operating system to recognize and access logical volumes. An LVM-enabled operating system includes OS2LVM.DMD, LVMALERT.EXE, and an LVM-aware version of OS2DASD.DMD in CONFIG.SYS, as well as an LVM-aware kernel. An LVM-enabled OS is not dependent on traditional drive letter assignment limitations.
Linux LVM is a tool to dynamically manipulate native disk space available to installed Linux operating systems.
A logical volume consists of one or more physical partitions assigned a single drive letter or virtual device space.
One job of any boot manager is to provide the user with an operating system selection menu when POST has completed. Once the boot manager has been installed and properly configured, you simply make a choice each time you see the menu.
The OS/2 and eCS installers will not install to any logical partition if IBM Boot Manager is not present. Once OS/2 is installed, some boot loaders can start it from any partition installed to. This leaves IBM Boot Manager technically unnecessary, but only as long as you don't need to reinstall.
Technically, it doesn't matter. Logistically, it can be more convenient to install Microsoft operating systems first, due to their proclivity to do as they please without giving you the option to do what you prefer. If you do all your partitioning before doing any operating system installations, this rude proclivity can be avoided. The key here is to make sure the Microsoft installer finds the partition(s) you want it to use ready to go, by properly formatting, and making sure its primary is set active. Note that only the Windows® initialization files need a visible primary partition, which can be quite small if you choose a logical for its main installation. Some Microsoft installers are broken such that as much as 40 MiB or so of freespace must be available on its primary for it to proceed.
An additional point to consider is the proclivity of Microsoft operating systems to require periodic reinstallation. Since other operating systems rarely need reinstallation, it's often necessary to install the Microsoft system after another has been installed and needs to remain undisturbed.
Something is wrong with your regular boot partition. How do you fix it if you can't boot it? You boot something else. Open files on your boot partition are preventing you from successfully backing up the whole partition. How do you back up the whole partition with open files on it? One way is to boot something else. You are trying to get a new app or hardware working right, and just started a shutdown to troubleshoot, then you remember something else you should have done first. If you boot maintenence, you can successfully and/or more quickly go back and do what you forgot, if your maintenance boot is capable of quickness.
In Windows®, your emergency boot diskette is your path to a maintenance boot. In Linux, the diskette you might have created when you installed is one path to a maintenance boot. In OS/2, you use the program object "create utility diskettes" after installing, then use these diskettes to maintenance boot, at least if you follow the instructions in the manuals. Floppy boots are slow and inconvenient. You have to first create them. Then you have to be able to find them when necessary. You have to be able to rely on them to work when called upon to work, easier said than done with floppy media. Lastly, you have to wait for that agonizingly slow floppy drive to maximize the time it takes to boot.
A maintenance partition is an extra partition on your hard disk designed to more reliably and quickly provide the function of a diskette boot. Key is reliability. It must not be subject to accidental corruption while using any other OS, yet ready at any time to quickly provide access to solving problems with other boot partitions.
A crude form of maintenance boot can involve no more than placing copies of the important device drivers in \OS2 and \OS2\BOOT on a partition adjacent to the boot partition. For example, if dealing with a lost letter, causing the boot drive letter to shift down to E: from the normal F:, boot might proceed to a command prompt anyway if the important drivers can be found on the drive that normally is E:. The opposite problem is an added letter, which commonly will occur on a system which when planned for failed to provide for a second visible primary partition, and a second visible primary appears because you are trying to recover files from an old disk added back after an upgrade to a new disk. If the normal boot drive is F:, and there is normally an available G:, boot might proceed to a command prompt anyway if the important drivers can be found on the drive that normally is G:.
No. But, unless you rarely need to maintenance boot, or you are comfortable with the wait on your floppy drive each time, or you and your PC are adept enough to perform maintenance needs from a CD boot or Linux, or you can't spare a few megabytes of hard disk space to put one on, then you should have one. A dedicated maintenance partition minimizes the inconvenience of maintenance better than the maintenance boot alternatives.
In order to minimize or eliminate risk of damage while booted elsewhere, it needs to be hidden or otherwise unavailable while booted elsewhere. The most practical way to provide this protection is on a first disk primary partition that is always hidden unless booted. If you have DOS or Windows® installed on another primary and use IBM Boot Manager, you can ensure the maintenace partition remains hidden by always booting the other primary last before booting any logical.
If the maintenance partition is LVM enabled, it will necessarily need to have a drive letter assigned to be able to boot, but since LVM drive letter assignments always apply until revoked, the maintenance partition should not be LVM-enabled, as that sticky letter will make it visible on all LVM-enabled boots, whether a hidden partition type or not.
All that is required is the same amount of space as on your floppy boot set. The minimum single cylinder size on large disks of 7.8 MiB is more than enough. For convenience, you'll probably want extra space for any utility software required to backup and restore or fix whatever is wrong with other partitions. Since maximum convenience for maintenance commonly equates to fastest bootup time, most maintenance partitions are set up without the overhead of a graphical interface. In the absence of a GUI, an OFM such as File Commander/2, a mere 280 KiB ZIP download, can greatly increase your maintenance productivity.
Copy the files from your maintenance diskettes and then run sysinstx, use BootOS2, or do a compact normal install from diskettes or CD. Install TSHELL if you want to provide simple text mode multitasking.
It depends. What it depends on and the procedures involved are outside the scope of this document, but Hard Disk Upgrade Mini How-To provdes some help for Linux users.
This is where you plan to install OS/2, MCP, eCS or WSeB when FDISK or LVM is called from the installation utility. At all other times installable is unavailable and irrelevant.
This is the primary partition with the active bit set in the master partition table. When the BIOS boot code has finished the POST it transfers control to the code in the master boot record, which first looks for the active partition bit in the partition table contained at the end of the boot sector, then in turn either loads the loader code from the first primary partition boot record, or transfers control to the boot record loader code of an active primary partition that is not the first primary partition. If LILO or Grub is installed in the master boot record, then the active flag(s), if set, are disregarded. If more than one primary partition on a single HD has its active flag set, DOS and OS/2 will not boot.
This is the OS/2 FDISK & LVM nomenclature for specifying the "active" partition on the first hard disk.
Literally capable of being booted. This can either be directly, as a result of the active byte set in a primary partition table entry, or indirectly, via a boot manager, in which case the partition may not need to be a primary partition.
Usually the same as "accessible". Traditionally it means the hidden status bit in the partition type byte in the partition table entry is not set. A special driver can sometimes be used to make visible (enable access) to a partition with its hidden bit set in the partition table entry.
This means not visible to a booting or booted OS, traditionally due to the hidden status bit in the partition type byte in the partition table entry. With newer OS versions it can also mean that access to the partition has not explicitly been enabled by a storage device access manager.
This means the active flag is not set in the partition table entry, which means the partition will be bypassed by the BIOS in seeking the sector to requish boot control to. Some use it to mean that the partition type byte's hidden bit is set.
This option is greyed out unless FDISK or LVM is called from the OS/2, MCP, eCS or WSeB installation utility. At all other times "set installable" is unavailable and irrelevant. It is a setting that does not survive a boot.
This can happen if you forget to forget to first create a logical volume with LVM, or if you encounter the 1024 cylinder or type F problems.
This is not always possible. Hard disks have grown much larger than ever anticipated by early BIOS designs. In nearly all cases, correct detection requires the BIOS to be set to automatically detect each disk anew on each boot. Usually this is done in the very first BIOS setup screen by choosing "AUTO" for every setting for which it is provided.
Recent BIOS routinely provide an option on another screen to autodetect the disk. This option fixes the values on the first screen to other than "AUTO". Unfortunately, these values are often set incorrectly on large disks, so it is best to avoid the autodetect BIOS option.
If setting the BIOS to "AUTO" and "AUTO" fails to get your disk recognized, a BIOS upgrade may be available to solve the problem. If not, the obstacle is probably that your disk is larger than your BIOS can recognize. These limits typically fall at 2, 4, 8, 32, 64, or 127 GB. Limits of 8 & 32 are currently the most frequently encountered. Many newer drives have either an optional jumper setting or software available from the drive maker that can be used to enable the drive to be seen by the BIOS as within these limits.
If neither a BIOS upgrade nor an artifical size limitation are available to enable your large disk to be accessed, other options can be used, such as a PCI card disk controller (modest cost), a new motherboard (expensive), or software provided by the disk manufacturer (free, but with side effects, and so recommended only as an absolute last resort).
Lastly, as long as you don't need to boot from it, modern operating systems will find it even though the BIOS won't. In this case, enable the drive controller in the BIOS, but set the BIOS HD option to NONE or NOT INSTALLED.