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Re: Building a multiboot system!

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"dg1261" <dgREMOVE-THIS1261@cs.com> wrote in message 
news:XnsA29D9450C299dgREMOVETHIS1261csco@78.46.70.116...
> "Rod Pemberton" <dont_use_email@xnohavenotit.cnm> wrote in
> news:op.w8fjz9wg5zc71u@localhost:
>
>>> the FATs would need to be expanded so they have
>>> room to record the extra clusters.
>>
>> ... "has" to be adjusted or "may need" to be adjusted?
>>
>> I would think both the BPB and FAT sizes would be valid for a
>> certain range of partition sizes.  So, if the change is outside
>> that range, above or below, then they'd have to be adjusted.
>> If within, they shouldn't.  Assuming they're already set to the
>> maximums, it's even more likely they shouldn't need adjustment.
>
> IME, FATs have always occupied no more sectors than the absolute minimum
> necessary to represent the capacity of the partition.  So if you increase
> the size of the partition the FATs will always have to be increased.

The basic FAT type is officially based on the number of clusters, not the 
number of sectors. Microsoft OSes use their own official calculation. They 
explain the details in a document called fatgen103 - copies abound.

> Larger FATs will always entail adding at least one more sector to each
> FAT if more than 512/2 clusters are being added (since each cluster entry
> takes two bytes).  On a medium-sized FAT16 partition with clusters of
> 4KB, 256 clusters are only 1MB, so increasing the partition size by more
> than 1MB will always require adding more sectors for the FATs.
>
>
>>  From the RBIL BPB and extended BPB, I only see two fields that
>> would appear to need adjustment sometimes: "sectors per cluster"
>> and "sectors per FAT".
>
> ...which bring up another point: if a partition resize is drastic enough
> that it also requires a change in the cluster size (e.g., from 2KB
> clusters to 4KB or 8KB), that will additionally require rewriting every
> single FAT entry, as well as moving any occupied data sector that doesn't
> line up properly with the new cluster boundaries.

One more field may need adjustment: if the location of the partition changes 
a field needs to be updated. It might be called Reserved Sectors or 
something like that but is a field in the BPB which says where the FAT 
partition starts on the disk or, equivalently, how many sectors precede it.

James

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Thread

Building a multiboot system! Patrick Rockwell <prockwell@thegrid.net> - 2013-12-18 20:25 -0800
  Re: Building a multiboot system! JJ <duh@nah.meh> - 2013-12-19 13:01 +0700
    Re: Building a multiboot system! Patrick Rockwell <prockwell@thegrid.net> - 2013-12-19 17:37 -0800
      Re: Building a multiboot system! "Rod Pemberton" <dont_use_email@xnohavenotit.cnm> - 2013-12-20 02:16 -0500
        Re: Building a multiboot system! "Stanley Daniel de Liver" <admin@127.0.0.1> - 2013-12-20 11:30 +0000
          Re: Building a multiboot system! dg1261 <dgREMOVE-THIS1261@cs.com> - 2013-12-21 00:59 +0000
            Re: Building a multiboot system! "James Harris" <james.harris.1@gmail.com> - 2013-12-21 12:18 +0000
              Re: Building a multiboot system! "Stanley Daniel de Liver" <admin@127.0.0.1> - 2013-12-21 15:11 +0000
              Re: Building a multiboot system! "Rod Pemberton" <dont_use_email@xnohavenotit.cnm> - 2013-12-21 17:35 -0500
                Re: Building a multiboot system! "James Harris" <james.harris.1@gmail.com> - 2013-12-21 23:33 +0000
            Re: Building a multiboot system! "Stanley Daniel de Liver" <admin@127.0.0.1> - 2013-12-21 14:47 +0000
        Re: Building a multiboot system! Ross Ridge <rridge@csclub.uwaterloo.ca> - 2013-12-22 15:31 -0500
  Re: Building a multiboot system! dg1261 <dgREMOVE-THIS1261@cs.com> - 2013-12-19 11:29 +0000
    Re: Building a multiboot system! Harry Potter <rose.joseph12@yahoo.com> - 2013-12-19 08:10 -0800
      Re: Building a multiboot system! Patrick Rockwell <prockwell@thegrid.net> - 2013-12-19 13:37 -0800
      Re: Building a multiboot system! dg1261 <dgREMOVE-THIS1261@cs.com> - 2013-12-20 06:22 +0000
        Re: Building a multiboot system! "Rod Pemberton" <dont_use_email@xnohavenotit.cnm> - 2013-12-20 02:16 -0500
          Re: Building a multiboot system! "Stanley Daniel de Liver" <admin@127.0.0.1> - 2013-12-20 11:15 +0000
          Re: Building a multiboot system! dg1261 <dgREMOVE-THIS1261@cs.com> - 2013-12-21 00:56 +0000
            Re: Building a multiboot system! "Rod Pemberton" <dont_use_email@xnohavenotit.cnm> - 2013-12-21 01:51 -0500
              Re: Building a multiboot system! dg1261 <dgREMOVE-THIS1261@cs.com> - 2013-12-21 08:54 +0000
                Re: Building a multiboot system! "James Harris" <james.harris.1@gmail.com> - 2013-12-21 12:26 +0000
              Re: Building a multiboot system! Steph <pas.de.mail@serveur.invalid> - 2013-12-21 15:11 +0000
    Re: Building a multiboot system! Patrick Rockwell <prockwell@thegrid.net> - 2014-02-07 14:15 -0800
      Re: Building a multiboot system! dg1261 <dgREMOVE-THIS1261@cs.com> - 2014-02-08 09:41 +0000
  Re: Building a multiboot system! miepbart@gmail.com - 2014-08-17 00:02 -0700

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