brown@nicmad.UUCP (08/07/85)
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As mentioned in my previous posting, here is the CLUSTER.TXT file that I
also got off of our BBS.
2K Cluster Size for 10MB Fixed Disks under DOS 3.x
Standard 10mb fixed disks formatted under DOS 3.0 & 3.1 utilize 4k
clusters (i.e., the minimum space allocated to any file is 4096 bytes),
while drives 20mb and larger utilize 2k clusters. At work, I use a PC
with twin 10mb drives under DOS 3.1. Since I have a multitude of small
files on these disks, the smaller allocation unit's space saving
advantage far outweighs any theoretical disadvantage of additional
overhead for DOS to handle the added allocation units. With the help of
Bob Morse, Jim Gainsley, and the DOS Technical Reference, I was able to
make the changes necessary to use 2k clusters on both of my 10mb drives.
By following the step-by-step instructions below, you will be able to
make the switch to 2k clusters yourself. The need for making a complete
backup of all your files prior to attempting this procedure cannot be
overephasized. You will need the following tools:
(1) IBM PC-DOS version 3.1 (3.0 will work, but because of other bugs,
3.1 is strongly recommended).
(2) A disk utility such as Norton's NU.COM, or equivalent.
Most critical to the process is the sequence in which this procedure is
attempted. Here is the 4k to 2k cluster procedure:
(1) Do a complete backup of the drive, using your current version of
DOS.
(2) Cold boot DOS 3.1, and FDISK the drive to create a DOS partition.
(3) Format the drive using the DOS format program. Don't use any
parameters (no /s or /v).
(4) Using your Norton (or whatever), select the boot sector and view
it. See below for an explanation of the pertinent info in this
sector. You should see a value of 08 for sectors per cluster.
change this to 04. You should see a value of 0800 for sectors per
fat. Change this to 1500. All changes to the fat sectors required
for 2k clusters will be accomplished by the subsequent format
(6,below). No other manual changes are required. A more detailed
explanation of these two changes:
The number of sectors per cluster would change from 08 to 04, since
that's what this is all about. The sectors per FAT will change, in
order to accomodate (1) the increased number of possible FAT
entries, and (2) the increased size of each fat entry (new 16 vs.
old 12 bits each). The value to use for a 10 meg & 2k clusters
would be 21 sectors, or 1500 in hex word format.
(5) Exit Norton and do a cold boot. This is critical, since the boot
sector is read by DOS only once, at boot time, in order to build
the BIOS Parameter Block. Having different info in the boot
sector than what's in the memory-resident BPB will cause
exceedingly flaky things to happen, as you can imagine.
(6) Reformat the drive using the DOS program, using whatever switches
that you desire (/s or /v). Format will not affect your changes to
the boot sector.
(7) Restore your files, remembering to use the new restore switch (/P)
which prompts before restoring system files. If you restore an
old version of COMMAND.COM, make sure to copy a 3.x version over
it afterwards. You should now be operational again, with 2k
clusters.
--------------------
Example of first few bytes in the Boot Sector displayed in hex format,
after formatting with DOS 3.1, and prior to 2k cluster size changes:
EB299049 424D2020 332E3100 02080100 020002F3 50F80800
^^ ^^^^
AA BB
After the 2k cluster size changes:
EB299049 424D2020 332E3100 02040100 020002F3 50F81500
^^ ^^^^
AA BB
Where the data elements directly above AA are sectors per cluster,
and above BB are sectors per FAT.
Further info on the entries in the boot sector entries used to build
the BIOS Parameter Block can be found in the DOS 3.x Technical
Reference, Page 3-22. Of course, I cannot warrant that this change
will work for all controller/disk combinations, particularly for
controllers and drives which are not 'XT clones' though it 'should
work' for all drives compatible enough to work under DOS 3.x.
--
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{seismo!uwvax!|!decvax|!ihnp4}!nicmad!brown