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FORMAT - formats a new disk, clears the FAT and DIRECTORY
and optionally copies the SYSTEM and COMMAND.COM to this
new disk.
Command syntax:
FORMAT [drive:][/switch1][/switch2]...[/switch16]
Where "drive:" is a legal drive specification and if
omitted indicates that the default drive will be used.
There may be up to 16 legal switches included in the
command line.
The OEM must supply five (NEAR) routines to the program
along with 6 data items. The names of the routines are INIT,
control (by the Microsoft module) is like this:
| INIT |
+------------+ |
+------------+ |
|<-------+ |
+-----------+ |-This loop is done |- This loop done
| BADSECTOR | | for each group of | once for each disk
+-----------+ | bad sectors | to be formatted.
|----->--+ | If variable HARDFLAG
| | is set then the loop
+----------+ | is only performed
| | | once.
| WRTFAT | |
+----------+ |
| |
+------+ |
| DONE | |
+------+ |
The INIT, DISKFORMAT, and BADSECTOR routines are free
to use any MS-DOS system calls, except for calls that cause
disk accesses on the disk being formatted. DONE may use
ANY calls, since by the time it is called the new disk has
been formatted.
The following data must be declared PUBLIC in a module
provided by the OEM:
SWITCHLIST - A string of bytes. The first byte is count
N, followed by N characters which are the switches to
be accepted by the command line scanner. Alphabetic
characters must be in upper case (the numeric
characters 0-9 are allowed). The last three switches,
normally "O", "V" and "S", have pre-defined meanings.
The "S" switch is the switch which causes the
system files IO.SYS, MSDOS.SYS, and COMMAND.COM to be
transfered to the disk after it is formatted thus
making a "S"ystem disk. The switch can be some letter
other than "S", but the last switch in the list is
assumed to have the meaning "transfer system",
regardles of what the particular letter is.
The second to the last switch, "V", causes FORMAT
to prompt the user for a volume label after the disk
is formatted. Again, as with "S", the particular
letter is not important but rather the position in the
The third to the last switch, "O", causes FORMAT to
produce an IBM Personal Computer DOS version 1.X
compatible disk. Normally FORMAT causes a 0 byte to
be placed in the first byte of each directory entry
instead of the 0E5 Hex free entry designator. This
results in a very marked directory search performance
increase due to an optimization in the DOS. Disks
made this way cause trouble on IBM PC DOS 1.X
versions, however, which did not have this
optimization. The 0 byte fools IBM 1.X versions into
thinking these entries are allocated instead of free,
NOTE that IBM Personnal Computer DOS version 2.00 and
MS-DOS version 1.25 will have no trouble with these
disks, since they have the same optimization. The "O"
switch causes FORMAT to re-do the directory with a 0E5
Hex byte at the start of each entry so that the disk
may be used with 1.X versions of IBM PC DOS, as well
as MS-DOS 1.25/2.00 and IBM PC DOS 2.00. This switch
should only be given when needed because it takes a
fair amount of time for FORMAT to perform the
conversion, and it noticably decreases 1.25 and 2.00
performance on disks with few directory entries.
Up to 16 switches are permitted. Normally a "C"
switch is specified for "Clear". This switch should
cause the formatting operation to be bypassed (within
DISKFORMAT or BADSECTOR). This is provided as a
time-saving convenience to the user, who may wish
to "start fresh" on a previosly formatted and used
HARDFLAG - BYTE location which specifies whether the
OEM routine is formatting a fixed disk or a a drive
with removable media. A zero indicates removable
media, any other value indicates a fixed disk. The
status of this byte only effect the messages printed
by the main format module. This value should be
set or reset by the OEM supplied INIT routine.
FATID - BYTE location containing the value to be used
in the first byte of the FAT. Must be in the range
F8 hex to FF hex.
STARTSECTOR - WORD location containing the sector number
of the first sector of the data area.
FATSPACE - WORD location containing the address of the
start of the FAT area. A FAT built in this area
will be written to disk using the OEM supplied WRTFAT
subroutine. 6k is sufficient to store any FAT. This
area must not overlap the FREESPACE area.
FREESPACE - WORD location which contains the address
of the start of free memory space. This is where
the system will be loaded, by the Microsoft module,
for transferring to the newly formatted disk. Memory
should be available from this address to the end
of memory, so it is typically the address of the
end of the OEM module.
The following routines must be declared PUBLIC in the
OEM-supplied module:
INIT - An initialization routine. This routine is called
once at the start of the FORMAT run after the switches
have been processed. This routine should perform
any functions that only need to be done once per
FORMAT run. An example of what this routine might
do is read the boot sector into a buffer so that
it can be transferred to the new disks by DISKFORMAT.
If this routine returns with the CARRY flag set it
indicates an error, and FORMAT will print "Format
failure" and quit. This feature can be used to detect
conflicting switches (like specifying both single
and double density) and cause FORMAT to quit without
doing anything.
DISKFORMAT - Formats the disk according to the options
indicated by the switches and the value of FATID
must be defined when it returns (although INIT may
have already done it). This routine is called once
for EACH disk to be formatted. If neccessary it
must transfer the Bootstrap loader. If any error
conditions are detected, set the CARRY flag and return
to FORMAT. FORMAT will report a 'Format failure'
and prompt for another disk. (If you only require
a clear directory and FAT then simply setting the
appropriate FATID, if not done by INIT, will be all
that DISKFORMAT must do.)
BADSECTOR - Reports the sector number of any bad sectors
that may have been found during the formatting of
the disk. This routine is called at least once for
EACH disk to be formatted, and is called repeatedly
until AX is zero or the carry flag is set. The carry
flag is used just as in DISKFORMAT to indicate an
error, and FORMAT handles it in the same way. The
first sector in the data area must be in STARTSECTOR
for the returns from this routine to be interpreted
correctly. If there are bad sectors, BADSECTOR must
return a sector number in in register BX, the number
of consecutive bad sectors in register AX, and carry
clear. FORMAT will then process the bad sectors
and call BADSECTOR again. When BADSECTOR returns
with AX = 0 this means there are no more bad sectors;
FORMAT clears the directory and goes on to DONE,
so for this last return BX need not contain anything
FORMAT processes bad sectors by determining their
corresponding allocation unit and marking that unit
with an FF7 hex in the File Allocation Table. CHKDSK
understands the FF7 mark as a flag for bad sectors
and accordingly reports the number of bytes marked
in this way.
NOTE: Actual formatting of the disk can be done in
BADSECTOR instead of DISKFORMAT on a "report as you
go" basis. Formatting goes until a group of bad
sectors is encountered, BADSECTOR then reports them
by returning with AX and BX set. FORMAT will then
call BADSECTOR again and formatting can continue.
WRTFAT - This routine is called after the disk is
formatted and bad sectors have been reported. Its
purpose is to write all copies of the FAT from the
area of memory referenced by FATSPACE to the drive
just formatted. It may be possible to use INT 26H
to perform the write, or a direct BIOS call. Whether
this is possible depends on whether the FAT ID byte
is used by the BIOS to determine the media in the
drive. If it is, these methods will probably fail
because there is no FAT ID byte on the disk yet (in
this case WRTFATs primary job is to get the FAT ID
byte out on the disk and thus solve the chicken and
egg problem).
DONE - This routine is called after the formatting is
complete, the disk directory has been initialized,
and the system has been transferred. It is called
once for EACH disk to be formatted. This gives the
chance for any finishing-up operations, if needed.
If the OEM desires certain extra files to be put
on the diskette by default, or according to a switch,
this could be done in DONE. Again, as in BADSECTOR
and DISKFORMAT, carry flag set on return means an
error has occurred: 'Format failure' will be printed
and FORMAT will prompt for another disk.
The following data is declared PUBLIC in Microsoft's FORMAT
SWITCHMAP - A word with a bit vector indicating what
switches have been included in the command line. The
correspondence of the bits to the switches is
determined by SWITCHLIST. The right-most
(highest-addressed) switch in SWITCHLIST (which must
be the system transfer switch, normally "S")
corresponds to bit 0, the second from the right,
normally "V" to bit 1, etc. For example, if
SWITCHLIST is the string "7,'AGI2OVS'", and the user
specifies "/G/S" on the command line, then bit 6 will
be 0 (A not specified), bit 5 will be 1 (G specified),
bits 4,3,2 and 1 will be 0 (neither I,2,O or V
specified), and bit 0 will be 1 (S specified).
Bits 0,1 and 2 are the only switches used in
Microsoft's FORMAT module. These switches are used 1)
after INIT has been called, to determine if it is
necessary to load the system; 2) after the last
BADSECTOR call, to determine if the system is to be
written, E5 directory conversion is to be done, and/or
a volume label is to be asked for. INIT may force
these bits set or reset if desired (for example, some
drives may never be used as system disk, such as hard
disks). After INIT, the "S" bit may be turned off
(but not on, since the system was never read) if
something happens that means the system should not be
After INIT, a second copy of SWITCHMAP is made
internally which is used to restore SWITCHMAP for
each disk to be formatted. FORMAT itself will turn
off the system bit if bad sectors are reported in
the system area; DISKFORMAT and BADSECTOR are also
allowed to change the map. However, these changes
affect only the current disk being formatted, since
SWITCHMAP is restored after each disk. (Changes
made to SWITCHMAP by INIT do affect ALL disks.)
DRIVE - A byte containing the drive specified in the
command line. 0=A, 1=B, etc.
Once the OEM-supplied module has been prepared, it must linked
with Microsoft's FORMAT.OBJ module and the FORMES.OBJ module.
If the OEM-supplied module is called OEMFOR.OBJ, then the
following linker command will do:
This command will produce a file called FORMAT.EXE. FORMAT
has been designed to run under MS-DOS as a simple binary
.COM file. This conversion is performed by LOCATE (EXE2BIN)
with the command
which will produce the file FORMAT.COM.
; A Sample OEM module
; This segment must be
; named CODE, it must be
; PUBLIC, and it's
; classname must be 'CODE'
; Must declare data and routines PUBLIC
; This data defined in Microsoft-supplied module
; Read the boot sector into memory
; Set FATID to double sided if "D" switch specified
; Use the bit map in SWITCHMAP to determine
; what switches are set
TEST SWITCHMAP,8 ;Is there a "/C"?
JNZ CLEAR ; Yes -- clear operation
; requested jump around the
; format code
< format the disk >
; Transfer the boot from memory to the new disk
; Error return - set carry
< Set up call to write out a fat to disk>
< Write out one fat to disk>
< Decrement fat counter >
CLC ;Good return
; Default Single sided
SWITCHLIST DB 5,"DCOVS" ; "OVS" must be the last
; switches in the list
BOOT DB BOOTSIZE DUP(?) ; Buffer for the
; boot sector
FATBUF DB 6 * 1024 DUP(?) ; Fat buffer
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