Boot problem
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From: John John - MVP on 9 Mar 2010 10:14 Jeff Gaines wrote: > On 09/03/2010 in message <#knFfn4vKHA.1984(a)TK2MSFTNGP05.phx.gbl> John > John - MVP wrote: > >>> Is it possible both partitions were marked as active? >> >> That is impossible. > > Why do you say that? Because that is how it is, only one partition can be marked as active at any given time. If you mark another partition as active the active flag of the currently active partition will be removed. This is just the way things work on MBR disks, if there were more than one active partition the MBR IPL wouldn't know where to pass the boot process. When the computer is booted it goes something like this: 1- The boot order is set in the BIOS and the BIOS selects the device to be booted, in this case the hard disk. 2- The BIOS locates sector 0 on the hard disk and loads the MBR and then passes the boot process to the MBR. 3- The MBR locates the Active partition and loads the Boot Sector of the active partition and then in turn passes the boot process to the boot sector. 4- A bit of code is executed in the boot sector and this code finds and loads the designated boot loader, on NT systems it loads NTLDR and it then passes the boot process to the boot loader. In step #3 the MBR would be lost if there were to be more than one active partition so the flagging mechanism for the active partition doesn't allow this to happen, there can only be one active partition at any given time on the disk. You can move the active flag to another primary partition but you cannot flag more than one partition at a time. John
From: Jeff Gaines on 9 Mar 2010 11:49 On 09/03/2010 in message <#UkXjs5vKHA.4492(a)TK2MSFTNGP05.phx.gbl> John John - MVP wrote: >Jeff Gaines wrote: >>On 09/03/2010 in message <#knFfn4vKHA.1984(a)TK2MSFTNGP05.phx.gbl> John >>John - MVP wrote: >> >>>>Is it possible both partitions were marked as active? >>> >>>That is impossible. >> >>Why do you say that? > >Because that is how it is, only one partition can be marked as active at >any given time. If you mark another partition as active the active flag >of the currently active partition will be removed. This is just the way >things work on MBR disks, if there were more than one active partition the >MBR IPL wouldn't know where to pass the boot process. When the computer >is booted it goes something like this: That may be true using FDISK but I have certainly ended up with a PC with more than one drive with an active partition. It may have been when I fitted a 2nd drive from another PC or when I was playing with Linux. It is much harder to get out of than to get into in the first place. -- Jeff Gaines Dorset UK The facts, although interesting, are irrelevant
From: John John - MVP on 9 Mar 2010 12:27 Jeff Gaines wrote: > On 09/03/2010 in message <#UkXjs5vKHA.4492(a)TK2MSFTNGP05.phx.gbl> John > John - MVP wrote: > >> Jeff Gaines wrote: >>> On 09/03/2010 in message <#knFfn4vKHA.1984(a)TK2MSFTNGP05.phx.gbl> >>> John John - MVP wrote: >>> >>>>> Is it possible both partitions were marked as active? >>>> >>>> That is impossible. >>> >>> Why do you say that? >> >> Because that is how it is, only one partition can be marked as active >> at any given time. If you mark another partition as active the active >> flag of the currently active partition will be removed. This is just >> the way things work on MBR disks, if there were more than one active >> partition the MBR IPL wouldn't know where to pass the boot process. >> When the computer is booted it goes something like this: > > That may be true using FDISK but I have certainly ended up with a PC > with more than one drive with an active partition. It may have been when > I fitted a 2nd drive from another PC or when I was playing with Linux. > It is much harder to get out of than to get into in the first place. If you have more than one hard disk then of course you can have more than one active partition as each disk can have an active partition. But a single disk can only have one active partition, if by some glitch (or by ill designed tools) more than one partition is set to be active the disk will not be able to boot. Is it possible that glitches or ill designed tools might set more than one active partition on the disk? None of the Microsoft tools do this, but certainly other poorly designed tools might be able to screw up a disk and software glitches can and do happen so it may be possible for this to happen but I have never personally seen this... or been able to inadvertently do it with any of the disk tools that I have worked with. Of course some boot managers install special boot partitions on the disk and then from this special partition they can create hundreds of pseudo primary partitions and possibly assign so called "active" status to any or all of these partitions but these are not standard MBR defined partitions, they are proprietary to the third party boot manager. John
From: Tom on 9 Mar 2010 16:44 "John John - MVP" <audetweld(a)nbnet.nb.ca> wrote in message news:Osdy326vKHA.1692(a)TK2MSFTNGP04.phx.gbl... > Jeff Gaines wrote: >> On 09/03/2010 in message <#UkXjs5vKHA.4492(a)TK2MSFTNGP05.phx.gbl> John >> John - MVP wrote: >> >>> Jeff Gaines wrote: >>>> On 09/03/2010 in message <#knFfn4vKHA.1984(a)TK2MSFTNGP05.phx.gbl> John >>>> John - MVP wrote: >>>> >>>>>> Is it possible both partitions were marked as active? >>>>> >>>>> That is impossible. >>>> >>>> Why do you say that? >>> >>> Because that is how it is, only one partition can be marked as active at >>> any given time. If you mark another partition as active the active flag >>> of the currently active partition will be removed. This is just the way >>> things work on MBR disks, if there were more than one active partition >>> the MBR IPL wouldn't know where to pass the boot process. When the >>> computer is booted it goes something like this: >> >> That may be true using FDISK but I have certainly ended up with a PC with >> more than one drive with an active partition. It may have been when I >> fitted a 2nd drive from another PC or when I was playing with Linux. It >> is much harder to get out of than to get into in the first place. > > If you have more than one hard disk then of course you can have more than > one active partition as each disk can have an active partition. But a > single disk can only have one active partition, if by some glitch (or by > ill designed tools) more than one partition is set to be active the disk > will not be able to boot. > > Is it possible that glitches or ill designed tools might set more than one > active partition on the disk? None of the Microsoft tools do this, but > certainly other poorly designed tools might be able to screw up a disk and > software glitches can and do happen so it may be possible for this to > happen but I have never personally seen this... or been able to > inadvertently do it with any of the disk tools that I have worked with. > > Of course some boot managers install special boot partitions on the disk > and then from this special partition they can create hundreds of pseudo > primary partitions and possibly assign so called "active" status to any or > all of these partitions but these are not standard MBR defined partitions, > they are proprietary to the third party boot manager. > > John Well, since you corrected yourself, it certainly is possible. You did say that it was impossible, when I know I have done this on one single disk by creating two primary partitions, instead of the usual creation of the logical/extended flavor.
From: John John - MVP on 9 Mar 2010 17:06 Tom wrote: > > > "John John - MVP" <audetweld(a)nbnet.nb.ca> wrote in message > news:Osdy326vKHA.1692(a)TK2MSFTNGP04.phx.gbl... >> Jeff Gaines wrote: >>> On 09/03/2010 in message <#UkXjs5vKHA.4492(a)TK2MSFTNGP05.phx.gbl> John >>> John - MVP wrote: >>> >>>> Jeff Gaines wrote: >>>>> On 09/03/2010 in message <#knFfn4vKHA.1984(a)TK2MSFTNGP05.phx.gbl> >>>>> John John - MVP wrote: >>>>> >>>>>>> Is it possible both partitions were marked as active? >>>>>> >>>>>> That is impossible. >>>>> >>>>> Why do you say that? >>>> >>>> Because that is how it is, only one partition can be marked as >>>> active at any given time. If you mark another partition as active >>>> the active flag of the currently active partition will be removed. >>>> This is just the way things work on MBR disks, if there were more >>>> than one active partition the MBR IPL wouldn't know where to pass >>>> the boot process. When the computer is booted it goes something >>>> like this: >>> >>> That may be true using FDISK but I have certainly ended up with a PC >>> with more than one drive with an active partition. It may have been >>> when I fitted a 2nd drive from another PC or when I was playing with >>> Linux. It is much harder to get out of than to get into in the first >>> place. >> >> If you have more than one hard disk then of course you can have more >> than one active partition as each disk can have an active partition. >> But a single disk can only have one active partition, if by some >> glitch (or by ill designed tools) more than one partition is set to be >> active the disk will not be able to boot. >> >> Is it possible that glitches or ill designed tools might set more than >> one active partition on the disk? None of the Microsoft tools do >> this, but certainly other poorly designed tools might be able to screw >> up a disk and software glitches can and do happen so it may be >> possible for this to happen but I have never personally seen this... >> or been able to inadvertently do it with any of the disk tools that I >> have worked with. >> >> Of course some boot managers install special boot partitions on the >> disk and then from this special partition they can create hundreds of >> pseudo primary partitions and possibly assign so called "active" >> status to any or all of these partitions but these are not standard >> MBR defined partitions, they are proprietary to the third party boot >> manager. >> >> John > > Well, since you corrected yourself, it certainly is possible. You did > say that it was impossible, when I know I have done this on one single > disk by creating two primary partitions, instead of the usual creation > of the logical/extended flavor. We are not talking about "Primary Partitions", an MBR disk can have four primary partitions but only one of these primary partitions can be active at any given time. A primary partition is not necessarily an active partition. You can use the built-in Disk Management tool (or many other disk preparation tools) and create 4 primary partitions on the disk without any problems, making more than one of them active is another story altogether. John
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