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<p>The 4GB limit is a result of the fact that Garmin devices use
FAT16B without LFS (only the very oldest) and FAT32 (all the rest)
filesystems. Garmin devices do not support exFAT; though, devices
with rewritable firmware could be made to support exFAT. The
reason that FAT file systems are used are they are freely
available and work on Linux, Windows and Apple operating systems.<br>
</p>
<p>Please, see:<br>
<a class="moz-txt-link-freetext" href="https://en.wikipedia.org/wiki/File_Allocation_Table">https://en.wikipedia.org/wiki/File_Allocation_Table</a><br>
<a class="moz-txt-link-freetext" href="https://physics.nist.gov/cuu/Units/binary.html">https://physics.nist.gov/cuu/Units/binary.html</a><br>
<a class="moz-txt-link-freetext" href="https://en.wikipedia.org/wiki/ExFAT">https://en.wikipedia.org/wiki/ExFAT</a><br>
</p>
<p>There are several sizes of concern: cluster size, maximum file
size, maximum number of files, and maximum file system size. Each
of these sizes are powers of two or powers of 2 less one. Because
of the powers of 2, SI binary prefixes will be used. Remember only
one file can be stored in a cluster and a file may have more than
one cluster. The space at the end of the last cluster of a file is
wasted.<br>
</p>
<p>FAT12 4KiB and 8KiB clusters, file size limited by volume size,
4068 files with 8 KiB clusters, 16MiB with 4KiB and 32MiB with 8
KiB clusters.</p>
<p>FAT16B minimum file system sizes 8 MiB with 128, 32 MiB with
512*, and 256 MiB 4 KiB disk logical sector sizes, 2GiB-1 without
LFS and 4GiB-1 with LFS, cluster sizes are powers of 2 from 512 to
32768, 65460 files with 32 KiB clusters, maximum file systems size
is 65525 clusters.</p>
<p>FAT32 32 MiB-4.5 KiB (with 65525 clusters and 512 byte sectors)
and 256 MiB-36 KiB (with 65525 clusters and 4 KiB sectors), same
filesize limits as FAT16B, cluster sizes that are powers of 2 from
512 to 2,097,152.</p>
<p>exFAT maximum file size practical 128 PiB-1, structural limit 16
EiB-1, maximum volume size practical 128 PiB, maximum number of
files per directory 2,796,202.<span style="color: rgb(0, 0, 0);
font-family: sans-serif; font-size: 12.32px; font-style: normal;
font-variant-ligatures: normal; font-variant-caps: normal;
font-weight: 400; letter-spacing: normal; orphans: 2;
text-align: left; text-indent: 0px; text-transform: none;
white-space: normal; widows: 2; word-spacing: 0px;
-webkit-text-stroke-width: 0px; background-color: rgb(248, 249,
250); text-decoration-style: initial; text-decoration-color:
initial; display: inline !important; float: none;"></span><br>
<span style="color: rgb(0, 0, 0); font-family: sans-serif;
font-size: 12.32px; font-style: normal; font-variant-ligatures:
normal; font-variant-caps: normal; font-weight: 400;
letter-spacing: normal; orphans: 2; text-align: left;
text-indent: 0px; text-transform: none; white-space: normal;
widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px;
background-color: rgb(248, 249, 250); text-decoration-style:
initial; text-decoration-color: initial; display: inline
!important; float: none;"></span></p>
<p>* almost all non CHR disks are 512 byte sectored.</p>
<p>People will tell you that you can not use a SD card larger than a
certain size dependent on Garmin receiver model. This is not true.
The actual requirement is that a Garmin receiver only looks that
the first primary partition on a SD card. Simply, divide the SD
card into two partitions (in Windows, the disk manager can do
this), format that partition as the appropriate FAT format, and
put the map or maps there. The second partition can be formatted
as one desires and used as desired. This is a handy space in which
to store other previously made maps or even a complete map
building system. I have done this on Garmin receivers as old as
Garmin StreetPilot 2610 with SD cards as large as 256 GB (the card
uses some of the memory for its management purposes).<br>
</p>
<div class="moz-cite-prefix">On 10/18/2020 2:14 AM, Carlos Dávila
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:62c988c5-3215-523a-4462-d56f43cb99eb@alternativaslibres.org">As
far as I know, mkgmap is able to produce unlimited size gmapsupp
files, but SD cards and internal device memories have a limit of 4
GB in a single file. To overcome that limit, recent versions of
Garmin City Navigator maps are split into several gmapsupp that
work as a single one in devices which include them. Would it be
possible to add an option to mkgmap, so that it automatically
splits gmapsupp when you process a map that is larger than 4 GB?
<br>
<br>
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<br>
<a class="moz-txt-link-freetext" href="http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev">http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev</a>
<br>
</blockquote>
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