Is there any limit on number of OS installed on a PC??

Hey i was thinking as to how many OS can someone possibly install in a single PC.. I have personally tried just 4 at a time on my PC... Is there any practical limit to it.. May be the space limitation on the buffer size of the initial boot loader space.. Are there any such limitations??

Reply to
adonis
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No. There may be a theoretical limit, but I've found no practical limit.

I've no clue what that means.

It's limited pretty much by the disk partitioning/labelling scheme (and the bootloader's ability to deal with large numbers of parititions). You'd have to tell us what bootloader and disk labelling scheme you're using to get a real answer.

At one point I had 12 or 13 different Linux distros installed on a single hard drive (each distro in its own partition). I was using Grub and the normal "DOS" disk labelling.

I could have installed more, but I didn't need to.

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Grant Edwards                   grante             Yow!  Edwin Meese made me
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Reply to
Grant Edwards

Limited to the number of programs you can put on it.

No space limitations, have the boot loader load up an "OS selector" program, which is virtually unlimited.

However, if they all have different file systems, then you start looking at how the disk is partitioned, etc.

Some OS's will play nice in other's sandboxes. Some may not.

Rufus

Reply to
Rufus V. Smith

By that i meant that a boot loader has so many entries stored for different OS... if there is a separate space for that.. then there might be a Space constraint..

the usual Grub or lilo boot loader...

Reply to
adonis

The initial boot code must be under 372bytes but that can be used to launch any program you fancy so the bootloader can be as big or as small as you like and there are no hard buffer size limits.

If you are using one FAT per OS though, then only one byte is allocated in the boot sector for the number of FATs on the disc which would limit you to 256 OSs.

Of course, you could have as many removable hard-drives/CDs/other bootable media as you like so the number of OSs is actually unlimited.

I think installing more than 4 OSs on a PC is on the slippery slope to disaster though.

Reply to
Tom Lucas

Where are these 372 bytes located... Is it on the harddisk or some other PROM or something similar... can you please elaborate on this... Why only 372 bytes were decided??

What about the popular Ext2 and Ext3 file systems... how many bytes are allocated in boot sector for OS using such FS...

Reply to
adonis

Op 15 Nov 2006 09:54:09 -0800 schreef adonis:

In the bootsector ... First sector on a floppy or the master boot partition on a HD.

The bootsector is read before any FS is initialised. GIYF, try "boot sector" or something like that.

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Coos
Reply to
Coos Haak

Indeed, bootloaders such as grub or lilo do just that: load a second-stage bootloader. In the case of grub, it knows a few filesystems, so the amount of bootloader "entries" is limited only by disk space.

What's a FAT in this context? All the google hits I find reger to the various MS "FAT" filesystem types.

Nah, I've done it many times, and it's not difficult at all.

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Grant Edwards                   grante             Yow!  PIZZA!!
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Reply to
Grant Edwards

But still Why 372??.. Why not 384 or 512 bytes...

Reply to
adonis

Op 15 Nov 2006 12:27:31 -0800 schreef adonis:

1) Learn to quote, don't snip attribution (who wrote that part) 2) Stay in the thread. I wrote this, you answered to Grant Edwards. 3) Find a book or find website that answers your questions. 4) 372? It's hidden in history of years ago..
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Coos
Reply to
Coos Haak

Kinda of-topic for this group.

I think that without some serious boot management, four is the limit. If you *really* want to get crazy, run a virtual server on your machine and load as many as you want under it.

Reply to
Jim Stewart

I wish folks who claim "off-topic" would include one or more of the following:

1) Why it is off topic. 2) What would be considered on-topic. 3) What would be the appropriate newsgroup for the question.

It just happens to be that c.a.e is the newsgroup where the brightest and most helpful folks with the largest breadth and depth of knowledge in software and hardware issues tend to pass through. On occasion I count myself as one of them.

Rufus

P.S. I looked for comp.os.multiple-os and didn't find it on my news server. comp.os had only two spam messages when I looked.

Reply to
Rufus V. Smith

I am not sure what this reference is to. The primary boot sector (the first sector on the disk that the BIOS loads to start the boot process) must have a structure that matches the BIOS requirements -- it must have a signature (55AAh, I think) in the last two bytes. And it must allocate 4 partition descriptors (16 bytes each) for up to 4 "primary" partitions, even if the system has no partition based file systems.

Likewise, it is executed, so there has to be enough code to load the second stage boot loader, typically it loads the first sector(s) of the "active" partition. Complicating this, some (most?, all?) modern system BIOSes skip this code and just boot the "active" partition directly. That means you almost have to use the traditional Microsoft boot logic in the primary boot sector, because it may or it may not be executed.... And the active parition boot sector is where the "real" smarts reside.

I think the OS|2 boot manager actually allocated a whole partition for itself, just to limit what the OSes had to accomodate should it be in that OS's partition.

Of course, if you are running grub or lilo, you have to worry about "FAT" OSes because that is one of the sets of considerations that the authors of gurb and lilo made. There is no inherent limitation on the number of OSes other than the size of the hard drive, until you consider the individual OSes (assuming you are writing the boot loader). Linux 0.x had some constraints which differ from those of Linux 2.x, which differ from those of MSDOS 6.x, which differ from those of Windows 95, 98SE, NT, 2K, XP and probably Vista. But a boot loader can be made compatible with this set. It does get harder if you include earlier versions of DOS, older versions of Unix, Netware, most RTOSes or your own custom OS (unless you use a drive format modeled on one of those).

For example, if you have two OSes both using a file system that does not support drive partitioning, getting around that can involve customized drivers in at least one OS, a "smart" disk controller to do the partitioning in hardware, or if the two OSes use the same non-partitioned file system, careful file isolation (similar to booting DOS and Windows NT residing in the same FAT16 partition).

The real answer is "it depends on the OSes you want to install" as well as "it depends on how much code you want written/run" -- go buy System Commander if you want to really push it. Or use grub if you are happy with a few or a vast number of somewhat similar OSes (I think limited to Linux, Microsoft, and compatible file systems).

For that matter, you can install four OSes in the Windows 2K+ and Linux families (with some effort) without any special software. I would still recommend gurb or lilo though for systems including Linux or Linux compatible OSes, just for convenience. Linux almost assumes lilo or grub today.

Reply to
Charles Marslett

Or more -- think removable hard drives (I've used those in the past).

And some systems (the Dell XPS710, for example) support a lot of SATA drives -- if booting from individual drives is supported, that's perhaps 10 or more drives x 4 (assuming the power supply and the physical size of the system accomodate it). Likewise for SCSI, and more likely to support booting from any drive.

Reply to
Charles Marslett

Because it lives in the boot sector along with a bunch of other information. The sector is 512 bytes, but there is a bunch of information stored in it along with the boot loader. There are 372 bytes left over for the boot loader. Here's a description of the format of the boot sector:

formatting link

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   Wim Lewis , Seattle, WA, USA. PGP keyID 27F772C1
Reply to
Wim Lewis

That link was really informative... thank you Lewis..

Regards, adonis

Reply to
adonis

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