Index: bootcd/isolinux/syslinux-6.03/doc/memdisk.txt
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--- bootcd/isolinux/syslinux-6.03/doc/memdisk.txt	(revision e16e8f2a41938d263af54a9fd6b4020d6c0d69fa)
+++ bootcd/isolinux/syslinux-6.03/doc/memdisk.txt	(revision e16e8f2a41938d263af54a9fd6b4020d6c0d69fa)
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+[This documentation is rather crufty at the moment.]
+
+MEMDISK is meant to allow booting legacy operating systems via PXE,
+and as a workaround for BIOSes where ISOLINUX image support doesn't
+work.
+
+MEMDISK simulates a disk by claiming a chunk of high memory for the
+disk and a (very small - 2K typical) chunk of low (DOS) memory for the
+driver itself, then hooking the INT 13h (disk driver) and INT 15h
+(memory query) BIOS interrupts.
+
+MEMDISK allows for an OS to detect the MEMDISK instance.  (See the
+"Additional technical information" section below.)
+
+To use it, type on the Syslinux command line:
+
+memdisk initrd=diskimg.img
+
+... where diskimg.img is the disk image you want to boot from.
+
+[Obviously, the memdisk binary as well as your disk image file need to
+be present in the boot image directory.]
+
+... or add to your syslinux.cfg/pxelinux.cfg/isolinux.cfg something like:
+
+label dos
+    kernel memdisk
+    append initrd=dosboot.img
+
+Note the following:
+
+a) The disk image can be uncompressed or compressed with gzip or zip.
+
+b) If the disk image is less than 4,194,304 bytes (4096K, 4 MB) it is
+   assumed to be a floppy image and MEMDISK will try to guess its
+   geometry based on the size of the file.  MEMDISK recognizes all the
+   standard floppy sizes as well as common extended formats:
+
+     163,840 bytes  (160K) c=40 h=1 s=8		5.25" SSSD
+     184,320 bytes  (180K) c=40 h=1 s=9		5.25" SSSD
+     327,680 bytes  (320K) c=40 h=2 s=8		5.25" DSDD
+     368,640 bytes  (360K) c=40 h=2 s=9		5.25" DSDD
+     655,360 bytes  (640K) c=80 h=2 s=8		3.5"  DSDD
+     737,280 bytes  (720K) c=80 h=2 s=9		3.5"  DSDD
+   1,222,800 bytes (1200K) c=80 h=2 s=15	5.25" DSHD
+   1,474,560 bytes (1440K) c=80 h=2 s=18	3.5"  DSHD
+   1,638,400 bytes (1600K) c=80 h=2 s=20	3.5"  DSHD (extended)
+   1,720,320 bytes (1680K) c=80 h=2 s=21	3.5"  DSHD (extended)
+   1,763,328 bytes (1722K) c=82 h=2 s=21	3.5"  DSHD (extended)
+   1,784,832 bytes (1743K) c=83 h=2 s=21	3.5"  DSHD (extended)
+   1,802,240 bytes (1760K) c=80 h=2 s=22	3.5"  DSHD (extended)
+   1,884,160 bytes (1840K) c=80 h=2 s=23	3.5"  DSHD (extended)
+   1,966,080 bytes (1920K) c=80 h=2 s=24	3.5"  DSHD (extended)
+   2,949,120 bytes (2880K) c=80 h=2 s=36	3.5"  DSED
+   3,194,880 bytes (3120K) c=80 h=2 s=39	3.5"  DSED (extended)
+   3,276,800 bytes (3200K) c=80 h=2 s=40	3.5"  DSED (extended)
+   3,604,480 bytes (3520K) c=80 h=2 s=44	3.5"  DSED (extended)
+   3,932,160 bytes (3840K) c=80 h=2 s=48	3.5"  DSED (extended)
+
+   A small perl script is included in the MEMDISK directory which can
+   determine the geometry that MEMDISK would select for other sizes;
+   in general MEMDISK will correctly detect most physical extended
+   formats used, with 80 cylinders or slightly more.
+
+   If the image is 4 MB or larger, it is assumed to be a hard disk
+   image, and should typically have an MBR and a partition table.  It
+   may optionally have a DOSEMU geometry header; in which case the
+   header is used to determine the C/H/S geometry of the disk.
+   Otherwise, the geometry is determined by examining the partition
+   table, so the entire image should be partitioned for proper
+   operation (it may be divided between multiple partitions, however.)
+
+   You can also specify the geometry manually with the following command
+   line options:
+
+   c=#		Specify number of cylinders (max 1024[*])
+   h=#		Specify number of heads (max 256[*])
+   s=#		Specify number of sectors (max 63)
+   floppy[=#]	The image is a floppy image[**]
+   harddisk[=#]	The image is a hard disk image[**]
+   iso		The image is an El Torito ISO9660 image (drive 0xE0)
+
+   # represents a decimal number.
+
+    [*] MS-DOS only allows max 255 heads, and only allows 255 cylinders
+        on floppy disks.
+
+   [**] Normally MEMDISK emulates the first floppy or hard disk.  This
+        can be overridden by specifying an index, e.g. floppy=1 will
+        simulate fd1 (B:). This may not work on all operating systems
+        or BIOSes.
+
+c) The disk is normally writable (although, of course, there is
+   nothing backing it up, so it only lasts until reset.)  If you want,
+   you can mimic a write-protected disk by specifying the command line
+   option:
+
+   ro		Disk is readonly
+
+d) MEMDISK normally uses the BIOS "INT 15h mover" API to access high
+   memory.  This is well-behaved with extended memory managers which load
+   later.  Unfortunately it appears that the "DOS boot disk" from
+   WinME/XP *deliberately* crash the system when this API is invoked.
+   The following command-line options tells MEMDISK to enter protected
+   mode directly, whenever possible:
+
+   raw		Use raw access to protected mode memory.
+
+   bigraw	Use raw access to protected mode memory, and leave the
+		CPU in "big real" mode afterwards.
+
+   int		Use plain INT 15h access to protected memory.  This assumes
+   		that anything which hooks INT 15h knows what it is doing.
+
+   safeint	Use INT 15h access to protected memory, but invoke
+		INT 15h the way it was *before* MEMDISK was loaded.
+		This is the default since version 3.73.
+
+e) MEMDISK by default supports EDD/EBIOS on hard disks, but not on
+   floppy disks.  This can be controlled with the options:
+
+   edd		Enable EDD/EBIOS
+   noedd	Disable EDD/EBIOS
+
+f) The following option can be used to pause to view the messages:
+
+   pause	Wait for a keypress right before booting
+
+g) The following option can be used to set the real-mode stack size.
+   The default is 512 bytes, but if there is a failure it might be
+   interesting to set it to something larger:
+
+   stack=size   Set the stack to "size" bytes
+
+h) Some systems without a floppy drive have been known to have
+   problems with floppy images.  To avoid that those problems, first
+   of all make sure you don't have a floppy drive configured on the
+   BIOS screen.  If there is no option to configure that, or that
+   doesn't work, you can use the option:
+
+   nopass	Hide all real drives of the same type (floppy or hard disk)
+   nopassany    Hide all real drives (floppy and hard disk)
+
+i) The following standard Linux option will mark memory as reserved.
+   Please note that the Syslinux core already loads MEMDISK and its
+   initrd below this point:
+
+   mem=size	Mark available memory above this point as Reserved.
+
+
+Some interesting things to note:
+
+If you're using MEMDISK to boot DOS from a CD-ROM (using ISOLINUX),
+you might find the generic El Torito CD-ROM driver by Gary Tong and
+Bart Lagerweij useful.  It is now included with the Syslinux
+distribution, in the dosutil directory.  See the file
+dosutil/eltorito.txt for more information.
+
+Similarly, if you're booting DOS over the network using PXELINUX, you
+can use the "keeppxe" option and use the generic PXE (UNDI) NDIS
+network driver, which is part of the PROBOOT.EXE distribution from
+Intel:
+
+	http://www.intel.com/support/network/adapter/1000/software.htm
+
+
+Additional technical information:
+
+Starting with version 2.08, MEMDISK now supports an installation check
+API.  This works as follows:
+
+	EAX = 454D08xxh ("ME") (08h = parameter query)
+	ECX = 444Dxxxxh ("MD")
+	EDX = 5349xxnnh	("IS") (nn = drive #)
+	EBX = 3F4Bxxxxh ("K?")
+	INT 13h
+
+If drive nn is a MEMDISK, the registers will contain:
+
+	EAX = 4D21xxxxh	("!M")
+	ECX = 4D45xxxxh ("EM")
+	EDX = 4944xxxxh ("DI")
+	EBX = 4B53xxxxh ("SK")
+
+	ES:DI -> MEMDISK info structures
+
+The low parts of EAX/ECX/EDX/EBX have the normal return values for INT
+13h, AH=08h, i.e. information of the disk geometry etc.
+
+See Ralf Brown's interrupt list,
+http://www.cs.cmu.edu/afs/cs.cmu.edu/user/ralf/pub/WWW/files.html or
+http://www.ctyme.com/rbrown.htm, for a detailed description.
+
+The MEMDISK info structure currently contains:
+
+	[ES:DI]		word	Total size of structure (currently 30 bytes)
+	[ES:DI+2]	byte	MEMDISK minor version
+	[ES:DI+3]	byte	MEMDISK major version
+	[ES:DI+4]	dword	Pointer to MEMDISK data in high memory
+	[ES:DI+8]	dword	Size of MEMDISK data in sectors
+	[ES:DI+12]	16:16	Far pointer to command line
+	[ES:DI+16]	16:16	Old INT 13h pointer
+	[ES:DI+20]	16:16	Old INT 15h pointer
+	[ES:DI+24]	word	Amount of DOS memory before MEMDISK loaded
+	[ES:DI+26]	byte	Boot loader ID
+	[ES:DI+27]	byte	Sector size as a power of 2
+				(If zero, assume 512-byte sectors)
+	[ES:DI+28]	word	If nonzero, offset (vs ES) to installed DPT
+				This pointer+16 contains the original INT 1Eh
+
+Sizes of this structure:
+
+3.71+		30 bytes	Added DPT pointer
+3.00-3.70	27 bytes	Added boot loader ID
+pre-3.00	26 bytes
+
+In addition, the following fields are available at [ES:0]:
+
+	[ES:0]		word	Offset of INT 13h routine (segment == ES)
+	[ES:2]		word	Offset of INT 15h routine (segment == ES)
+
+The program mdiskchk.c in the sample directory is an example on how
+this API can be used.
+
+The following code can be used to "disable" MEMDISK.  Note that it
+does not free the handler in DOS memory, and that running this from
+DOS will probably crash your machine (DOS doesn't like drives suddenly
+disappearing from underneath.)  This is also not necessarily the best
+method for this.
+
+	mov eax, 454D0800h
+	mov ecx, 444D0000h
+	mov edx, 53490000h
+	mov dl,drive_number
+	mov ebx, 3F4B0000h
+	int 13h
+
+	shr eax, 16
+	cmp ax, 4D21h
+	jne not_memdisk
+	shr ecx, 16
+	cmp cx, 4D45h
+	jne not_memdisk
+	shr edx, 16
+	cmp dx, 4944h
+	jne not_memdisk
+	shr ebx, 16
+	cmp bx, 4B53h
+	jne not_memdisk
+
+	cli
+	mov bx,[es:0]		; INT 13h handler offset
+	mov eax,[es:di+16]	; Old INT 13h handler
+	mov byte [es:bx], 0EAh	; FAR JMP
+	mov [es:bx+1], eax
+
+	mov bx,[es:2]		; INT 15h handler offset
+	mov eax,[es:di+20]	; Old INT 15h handler
+	mov byte [es:bx], 0EAh	; FAR JMP
+	mov [es:bx+1], eax
+	sti
+
+MEMDISK supports the Win9x "safe hook" structure for OS detection.
+(See "Safe Master Boot Record INT 13h Hook Routines," available at
+http://www.osronline.com/ddkx/w98ddk/storage_5l6g.htm as of
+December 7th, 2009.)  An OS driver can take a look at the INTerrupt table
+and try to walk along the chain of those hooks that implement the "safe hook"
+structure.  For each hook discovered, a vendor can be identified and the OS
+driver can take appropriate action.  The OS driver can mark the "flags" field
+of the "safe hook" to indicate that the driver has reviewed it already.  This
+prevents accidental re-detection, for example.
+
+MEMDISK adds one additional extension field to the "safe hook" structure, a
+pointer to a special MEMDISK structure called the "mBFT."  The mBFT is the
+"MEMDISK Boot Firmware Table" (akin to the iSCSI iBFT and the AoE aBFT).  An
+OS driver looking at MEMDISK's "safe hook" should know that this field will
+be present based on the fact that MEMDISK is the vendor identifier.
+
+The mBFT is little more than an ACPI table to prefix MEMDISK's traditional
+MEMDISK info structure (the "MDI").  The ACPI table's details are:
+
+  OEM ID. . . .: MEMDSK
+  OEM Table ID : Syslinux
+
+There is a 1-byte checksum field which covers the length of the mBFT all
+the way through to the end of the MEMDISK info structure.
+
+There is also a physical pointer to the "safe hook" structure associated
+with the MEMDISK instance.  An OS driver might use the following logic:
+
+  1. Walk INT 13h "safe hook" chain as far as possible, marking hooks as
+     having been reviewed.  For MEMDISK hooks, the driver then follows the
+     pointer to the mBFT and gathers the RAM disk details from the included
+     MDI.
+  2. The OS driver scans low memory for valid mBFTs.  MEMDISK instances that
+     have been "disconnected" from the INT 13h "safe hook" chain can be thus
+     discovered.  Looking at their associated "safe hook" structure will
+     reveal if they were indeed reviewed by the previous stage.
