Can a (second) hard disc consist of only 1 extended/logical partition? Or is at least one primary necessary?
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From: Jason Stacy on 19 Apr 2008 19:27 Assume I have a second hard disc in my system. Can I put only one extended/logical partiton on it? or is at least one primary partition per hard disc necessary? J.
From: Grant on 19 Apr 2008 21:03 On 19 Apr 2008 23:27:41 GMT, jjstacy(a)yahoo.net (Jason Stacy) wrote: >Assume I have a second hard disc in my system. >Can I put only one extended/logical partiton on it? Yes. Grant.
From: Aragorn on 19 Apr 2008 21:31 Jason Stacy wrote: > Assume I have a second hard disc in my system. > Can I put only one extended/logical partiton on it? Yes, you can. In fact, if GNU/Linux is your only operating system, you could even do that on your system disk. The Linux kernel doesn't care whether it lives in a partition that's either primary or logical. That's just legacy stuff from the days of DOS, and both OS/2 and Windows still require primary partitions to exist. The DOS-based versions of Windows needed to be installed in an active and primary partition starting within the first 32 MB of the disk volume, on the first disk found by the BIOS. For NT-based systems, only the bootloader and a few files need to exist in such a primary partition, while the rest can be installed in a logical partition in an extended partition container, or even on another disk. UNIX-style operating systems like GNU/Linux have traditionally not cared about the partition being primary or logical. > or is at least one primary partition per hard disc necessary? Negative, although you may be surprised to hear that even an extended partition container is in fact a primary partition. The definition "primary partition" simply means that it's a partition with its entry in the partition table in the disk's master boot record. Logical partitions have their partition entry in the extended partition container. The whole thing came to be when hard disks started becoming available with capacities that exceeded 32 MB, e.g. the 40 and 60 MB hard disk in the IBM PS/2 series. The FAT filesystem under DOS 3.xx could only handle 32 MB, so a second partition was needed to take advantage of the extra space, but DOS (and later on the DOS-based Windows versions) could only handle one primary partition per disk, so the concept of an extended partition container was born, i.e. a primary partition that holds other, logical partitions, together with a partition table for them. In addition, it was a solution for the fact that systems using the legacy /x86/ BIOS can only handle four primary partitions, while more partitions may be needed. However, systems with an EFI BIOS - this is still rare in the /x86/ world - can handle as much as 128 primary partitions per disk. Technically, you can even do without a partition at all for GNU/Linux and simply format the available diskspace, but this is not something I would advise. Especially for UNIX systems, I am much rather a proponent of using different partitions for specified branches of the filesystem hierarchy tree. For instance, you best split off */var* and */home* from the root filesystem, and have */tmp* exist on a /tmpfs./ I personally split off way more than that on my own systems and on our network's servers, but at least those(/three) two are the ones containing variable files and are thus best separated from the static data. Splitting certain subtrees off from the root filesystem also allows you to mount them with different options - e.g. read-only - or to even have them housing a different filesystem type. Either way and to summarize, if you're running an NT-based Windows on your system - e.g. XP or Vista - then only the partition containing the Windows bootloader needs to be primary (and marked active), regardless of whether you install the main Windows system in it or in another partition. Everything else can be a logical partition in an extended partition container. If on the other hand your system _only_ runs GNU/Linux, then none of it matters. The most common set-up for dual-booting systems with Windows and GNU/Linux is to have an active primary partition on the first disk in which you install Windows, and to use logical partitions on all disks from there on for both the Windows data partitions and the GNU/Linux partitions. -- Aragorn (registered GNU/Linux user #223157)
From: VanguardLH on 19 Apr 2008 21:59 Jason Stacy wrote: > Assume I have a second hard disc in my system. > Can I put only one extended/logical partiton on it? > > or is at least one primary partition per hard disc necessary? ------------------------------------------------------------ NOTE: FollowUp-To ignored. If your post was on-topic to each of the newsgroups to which you cross-posted then the continued discussion is also on-topic. Don't be rude by yanking away a discussion from visitors in the other newsgroups to what you like as your "home" group (since you can see the replies there, anyway, because you cross-posted). If you don't want to show the discussion there then don't cross-post there. ------------------------------------------------------------ You must meet all of the following conditions: x = 1 (or 0) to 4 primary partitions (*) y = 0 or 1 extended partition x + y = 1 to 4 partitions Or, put another way: - Primary partitions: 1 minimum (or 0 minimum) (*) 4 maximum - Extended partitions: 0 minimum 1 maximum - Total partition count: 1 minimum 4 maximum (*) The 1 minimum primary partition applies to the first hard disk that is detectable by the BIOS. After the BIOS completes its POST (power-on self test), it loads the bootstrap program from the MBR (master boot record) from the first hard disk that it finds. The first sector of the hard disk is the MBR and is not allocated to any partition (as well as the remaining 62 sectors of the first track on the hard since tracks are assigned in 63-sector increments). The first 446 bytes are the bootstrap program. So the BIOS needs to load the bootstrap program into memory and pass control to it. The BIOS *only* looks for the bootstrap program from the MBR on the *first* hard disk detected. The standard bootstrap program reads the partition table (also in the MBR on the first hard disk). It looks for which partition is marked "active". Only primary partitions can be marked with a status of active and only one primary partition can be active at a time. The bootstrap program uses the partition table information to figure out where the partitions reside. Partition entries in the MBR can only define areas within the same hard disk. So the bootstrap program finds which primary partition is active and that partition must be on that hard disk. The MBR bootstrap program then loads the OS boot loader starting in the first sector of the active (primary) partition. This is the old BIOS scheme of how to boot a system. The BIOS loads the bootstrap program in the MBR from the first detected hard disk which reads the partition tables in the same MBR to then load the OS boot loader in the primary partition marked as active and which can only reside on the same hard disk since partition tables only delineate areas on that hard disk. Other software-based schemes have evolved that replace the OS boot loader in the first sector of the partition (that the MBR bootstrap loaded), the OS loader lets you specify from where to load the actual OS (like Microsoft's dual-boot), or they replace the MBR bootstrap program to eliminate the restriction that the boot partition is primary or even has to be on the same hard disk. So with a multiboot manager replacement for the bootstrap program, you can boot to any type of partition (primary or to a logical drive under an extended partition) which can be on any hard disk. Some BIOSes have been extended to perform the same functionality as the software multiboot managers to allow booting from any partition or logical drive on any hard disk. So it depends on the capabilities of your BIOS and/or bootstrap program as to how you can setup your partitions. For the old BIOS scheme using a standard bootstrap program, you'll need a minimum of 1 primary partition on the first BIOS-detectable hard disk. For newer extended BIOS schemes or when replacing the MBR bootstrap program, your limits are still based on what that extended BIOS or multiboot software can do but those exceed what you could do under the old scheme. RTFM
From: Arno Wagner on 19 Apr 2008 22:55
In comp.sys.ibm.pc.hardware.storage Jason Stacy <jjstacy(a)yahoo.net> wrote: > Assume I have a second hard disc in my system. > Can I put only one extended/logical partiton on it? > or is at least one primary partition per hard disc necessary? It is advisable to avoid having a second primary parition, as Windows stupidly will give it the letter D: and shift all other letters. However, besides this little quirk that comes with the by now quite outdated and historic concept of drive letters, you can have an additional primary partion. In fact you can have up to 4 per disks, but again, that is likely a bad idea with Windows. Arno |