Difference between revisions of "MEMDISK"

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==What is MEMDISK?==
+
[[Category:MEMDISK]]
 +
[[Category:Menu]]
 +
 
 +
=What is MEMDISK?=
 
MEMDISK is meant to allow booting legacy operating systems.
 
MEMDISK is meant to allow booting legacy operating systems.
 
MEMDISK can boot floppy images, hard disk images and some ISO images.
 
MEMDISK can boot floppy images, hard disk images and some ISO images.
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==How can I use MEMDISK?==
+
=How can I use MEMDISK?=
MEMDISK is an auxillary module used in conjunction with a boot loader that can load linux kernels (EXTLINUX/ISOLINUX/PXELINUX/SYSLINUX, grub, grub4dos grub2, ...). You need a disk image as well as the memdisk file itself. As far as the bootloader is concerned, MEMDISK is the "kernel" and disk image is the initial ramdisk (initrd).
+
MEMDISK is an auxiliary module used in conjunction with a boot loader that can load linux kernels (EXTLINUX/ISOLINUX/PXELINUX/SYSLINUX, grub, grub4dos grub2, ...). You need a disk image as well as the memdisk file itself. As far as the bootloader is concerned, MEMDISK is the "kernel" and disk image is the initial ramdisk (initrd).
  
 
The disk image, passed as initrd, can be a '''compressed''' zip or gzip file.
 
The disk image, passed as initrd, can be a '''compressed''' zip or gzip file.
Line 14: Line 17:
  
  
===EXTLINUX/ISOLINUX/PXELINUX/SYSLINUX===
+
==EXTLINUX/ISOLINUX/PXELINUX/SYSLINUX==
 
You can use MEMDISK straight off the boot loader command line like the following:
 
You can use MEMDISK straight off the boot loader command line like the following:
 
  memdisk initrd=hdt.img
 
  memdisk initrd=hdt.img
Line 21: Line 24:
  
 
Normally, however, you would put something like following in the configuration file:
 
Normally, however, you would put something like following in the configuration file:
 +
<pre>
 
  # Boot Hardware Detection Tool from floppy image
 
  # Boot Hardware Detection Tool from floppy image
 
  LABEL hdt_floppy
 
  LABEL hdt_floppy
Line 37: Line 41:
 
   INITRD dosboot.img
 
   INITRD dosboot.img
 
   APPEND raw
 
   APPEND raw
 +
</pre>
  
===GRUB and GRUB4DOS===
+
==GRUB and GRUB4DOS==
 
In your '''menu.lst''' file, use something like:
 
In your '''menu.lst''' file, use something like:
 +
<pre>
 
  title Boot Hardware Detection Tool from floppy
 
  title Boot Hardware Detection Tool from floppy
 
   kernel /memdisk
 
   kernel /memdisk
Line 51: Line 57:
 
   kernel /memdisk raw
 
   kernel /memdisk raw
 
   initrd /dosboot.img
 
   initrd /dosboot.img
 +
</pre>
  
 
+
==GRUB2==
===GRUB2===
+
 
Add the following in your config scripts for grub2:
 
Add the following in your config scripts for grub2:
 +
 +
<pre>
 
  menuentry "Boot Hardware Detection Tool from floppy" {
 
  menuentry "Boot Hardware Detection Tool from floppy" {
 
   linux16 /memdisk
 
   linux16 /memdisk
Line 69: Line 77:
 
   initrd16 /dosboot.img
 
   initrd16 /dosboot.img
 
  }
 
  }
 +
</pre>
  
 
+
=Supported image types=
==Supported image types==
+
 
The image file should contain a disk image, either a floppy disk or hard disk image, or an iso image.
 
The image file should contain a disk image, either a floppy disk or hard disk image, or an iso image.
  
Line 77: Line 85:
  
  
===Floppy images===
+
==Floppy images==
 
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:
 
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:
  
 +
<pre>
 
     163,840 bytes  (160K) c=40 h=1 s=8 5.25" SSSD
 
     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
 
     184,320 bytes  (180K) c=40 h=1 s=9 5.25" SSSD
Line 100: Line 109:
 
   3,604,480 bytes (3520K) c=80 h=2 s=44 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)
 
   3,932,160 bytes (3840K) c=80 h=2 s=48 3.5"  DSED (extended)
 +
</pre>
  
 
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.
 
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.
  
 +
<pre>
 
  LABEL floppy_image
 
  LABEL floppy_image
 
   LINUX memdisk
 
   LINUX memdisk
 
   INITRD floppy.img
 
   INITRD floppy.img
 +
</pre>
  
 
If your image is larger than 4 MB and a floppy image, you can force MEMDISK to treat it as a floppy image:
 
If your image is larger than 4 MB and a floppy image, you can force MEMDISK to treat it as a floppy image:
 +
<pre>
 
  LABEL floppy_image
 
  LABEL floppy_image
 
   LINUX memdisk
 
   LINUX memdisk
 
   INITRD floppy.img
 
   INITRD floppy.img
 
   APPEND floppy
 
   APPEND floppy
 +
</pre>
  
 
+
==Hard disk images==
===Hard disk images===
+
 
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.)
 
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.)
  
 +
<pre>
 
  LABEL harddisk_image
 
  LABEL harddisk_image
 
   LINUX memdisk
 
   LINUX memdisk
 
   INITRD harddisk.img
 
   INITRD harddisk.img
 +
</pre>
  
 
If your image is smaller than 4 MB and it is a hard disk image, you can force MEMDISK to treat it as a hard disk image:
 
If your image is smaller than 4 MB and it is a hard disk image, you can force MEMDISK to treat it as a hard disk image:
 +
<pre>
 
  LABEL harddisk_image
 
  LABEL harddisk_image
 
   LINUX memdisk
 
   LINUX memdisk
 
   INITRD harddisk.img
 
   INITRD harddisk.img
 
   APPEND harddisk
 
   APPEND harddisk
 +
</pre>
  
 
+
==ISO images==
===ISO images===
+
 
For ISO images, the parameter 'iso' must be passed to MEMDISK.
 
For ISO images, the parameter 'iso' must be passed to MEMDISK.
 +
<pre>
 
  LABEL hdt_iso
 
  LABEL hdt_iso
 
   LINUX memdisk
 
   LINUX memdisk
 
   INITRD hdt.iso
 
   INITRD hdt.iso
 
   APPEND iso
 
   APPEND iso
 +
</pre>
  
 +
Sometimes
 +
  APPEND iso raw
 +
is the better "APPEND" option.
 +
 
It is possible to map and boot from some CD/DVD images using MEMDISK. No-emulation, floppy emulation and hard disk emulation ISO's are supported.
 
It is possible to map and boot from some CD/DVD images using MEMDISK. No-emulation, floppy emulation and hard disk emulation ISO's are supported.
 
"The "map" process is implemented using INT 13 - any disk emulation will remain accessible from an OS that uses compatible mode disk access, e.g. DOS and Windows 9x. The emulation via INT13 can't however, be accessed from an OS which uses protected mode drivers (Windows NT/2000/XP/2003/Vista/2008/7, Linux, FreeBSD) once the protected mode kernel drivers take control.
 
"The "map" process is implemented using INT 13 - any disk emulation will remain accessible from an OS that uses compatible mode disk access, e.g. DOS and Windows 9x. The emulation via INT13 can't however, be accessed from an OS which uses protected mode drivers (Windows NT/2000/XP/2003/Vista/2008/7, Linux, FreeBSD) once the protected mode kernel drivers take control.
  
  
===INT13 access: Not all images will boot completely!===
+
==INT13 access: Not all images will boot completely!==
  
====Real mode operating systems and boot loaders that use INT13 BIOS calls====
+
===Real mode operating systems and boot loaders that use INT13 BIOS calls===
 
DOS (MS-DOS, FreeDOS, DR-DOS, ...), Windows 95/98/ME and boot loaders (Syslinux, grub, grub4dos, gujin, gag, mbldr, ...) that use INT13 to read from disks will boot completely with MEMDISK (assuming that there are no BIOS bugs, or software bugs).
 
DOS (MS-DOS, FreeDOS, DR-DOS, ...), Windows 95/98/ME and boot loaders (Syslinux, grub, grub4dos, gujin, gag, mbldr, ...) that use INT13 to read from disks will boot completely with MEMDISK (assuming that there are no BIOS bugs, or software bugs).
  
====Windows NT/2000/XP/2003/Vista/2008/7 (NT based)====
+
===Windows NT/2000/XP/2003/Vista/2008/7 (NT based)===
 
These Windows versions use INT13 access only in the start of the booting process (loading only the necessary drivers). Once the protected mode drivers are functional to access the disks, Windows can't see the memory mapped drives created by MEMDISK (CD/DVD, hard disk and floppy disk images) and it will fail to boot completely.
 
These Windows versions use INT13 access only in the start of the booting process (loading only the necessary drivers). Once the protected mode drivers are functional to access the disks, Windows can't see the memory mapped drives created by MEMDISK (CD/DVD, hard disk and floppy disk images) and it will fail to boot completely.
  
  
 
'''Solutions:'''
 
'''Solutions:'''
=====- WinVBlock driver=====
+
====- WinVBlock driver====
 
WinVBlock is a Windows driver that overcomes this problem. It detects the MEMDISK mapped drives (CD/DVD, hard disk and floppy disk images) so Windows can read and write to those disks.
 
WinVBlock is a Windows driver that overcomes this problem. It detects the MEMDISK mapped drives (CD/DVD, hard disk and floppy disk images) so Windows can read and write to those disks.
  
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It will require the 'raw' parameter on some PCs.
 
It will require the 'raw' parameter on some PCs.
 +
<pre>
 
  LABEL windows_winvblock
 
  LABEL windows_winvblock
 
   LINUX memdisk
 
   LINUX memdisk
 
   INITRD windows_harddisk.img
 
   INITRD windows_harddisk.img
 
   APPEND raw
 
   APPEND raw
 +
</pre>
  
=====- Windows PE based=====
+
====- Windows PE based====
 
You can also build a RAM disk based Windows PE.
 
You can also build a RAM disk based Windows PE.
RAM disk based discs include Windows PE 2/2.1 and builds that utilize ramdisk.sys and setupldr.bin files from windows 2003 server SP1 source (see http://www.911cd.net/forums/index.php?showtopic=10482 and http://www.911cd.net/forums/index.php?showtopic=19333).
+
RAM disk based discs include Windows PE 2/2.1 and builds that utilize ramdisk.sys and setupldr.bin files from windows 2003 server SP1 source; see  
 +
* http://www.911cd.net/forums/index.php?showtopic=10482
 +
* http://www.911cd.net/forums/index.php?showtopic=19333
  
=====- Windows Vista/2008/7 with WIM images=====
+
====- Windows Vista/2008/7 with WIM images====
 
Windows Vista/2008/7 can be booted from a WIM image (loaded from disk via INT13).
 
Windows Vista/2008/7 can be booted from a WIM image (loaded from disk via INT13).
  
====Linux====
+
===Linux===
 
The majority of Linux based CD images will also fail to work with MEMDISK ISO emulation. Linux distributions require kernel and initrd files to be specified, as soon as these files are loaded the protected mode kernel driver(s) take control and the virtual CD will no longer be accessible. If any other files are required from the CD/DVD they will be missing, resulting in boot error(s).
 
The majority of Linux based CD images will also fail to work with MEMDISK ISO emulation. Linux distributions require kernel and initrd files to be specified, as soon as these files are loaded the protected mode kernel driver(s) take control and the virtual CD will no longer be accessible. If any other files are required from the CD/DVD they will be missing, resulting in boot error(s).
  
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 +
=Parameters and options=
  
 
+
==Specifying geometry and image type manually==
==Parameters and options==
+
 
+
 
+
===Specifying geometry and image type manually===
+
 
You can also specify the geometry manually with the following command line options:
 
You can also specify the geometry manually with the following command line options:
 
<pre>
 
<pre>
Line 197: Line 220:
 
         simulate fd1 (B:). This may not work on all operating systems
 
         simulate fd1 (B:). This may not work on all operating systems
 
         or BIOSes.</pre>
 
         or BIOSes.</pre>
 +
 
Example:
 
Example:
 +
<pre>
 
  # Boot harddisk image as second hard disk and specify C/H/S geometry
 
  # Boot harddisk image as second hard disk and specify C/H/S geometry
 
  LABEL hdt_floppy
 
  LABEL hdt_floppy
Line 203: Line 228:
 
   INITRD harddisk.img
 
   INITRD harddisk.img
 
   APPEND harddisk=1 c=255 h=64 s=22
 
   APPEND harddisk=1 c=255 h=64 s=22
 +
</pre>
  
===Set memory access method (raw, bigraw, int , safeint)===
+
==Set memory access method (raw, bigraw, int , safeint)==
 
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:
 
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:
  
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INT 15h the way it was *before* MEMDISK was loaded.
 
INT 15h the way it was *before* MEMDISK was loaded.
 
This is the default since version 3.73.</pre>
 
This is the default since version 3.73.</pre>
 +
 
It is possible that your image works fine without those parameters on some PCs or virtual machines, but fail to boot on other PCs. In this situation, adding 'raw' will normally solve your problem.
 
It is possible that your image works fine without those parameters on some PCs or virtual machines, but fail to boot on other PCs. In this situation, adding 'raw' will normally solve your problem.
  
 
Example:
 
Example:
 +
<pre>
 
  LABEL dos_with_extended_memory_manager
 
  LABEL dos_with_extended_memory_manager
 
   LINUX memdisk
 
   LINUX memdisk
 
   INITRD dos_emm.img
 
   INITRD dos_emm.img
 
   APPEND raw
 
   APPEND raw
 +
</pre>
  
 
+
==Write protected floppy and hard disk images==
===Write protected floppy and hard disk images===
+
 
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:
 
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
 
   ro          Disk is readonly
 
Example:
 
Example:
 +
<pre>
 
  # Simulate write protected floppy
 
  # Simulate write protected floppy
 
  LABEL hdt_write_protected_floppy
 
  LABEL hdt_write_protected_floppy
Line 236: Line 265:
 
   INITRD hdt.img
 
   INITRD hdt.img
 
   APPEND ro
 
   APPEND ro
 +
</pre>
  
 
+
==Hide real floppy or hard drive==
===Hide real floppy or hard drive===
+
 
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:
 
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:
 
+
<pre>
 
   nopass      Hide all real drives of the same type (floppy or hard disk)
 
   nopass      Hide all real drives of the same type (floppy or hard disk)
 
   nopassany    Hide all real drives (floppy and hard disk)
 
   nopassany    Hide all real drives (floppy and hard disk)
 +
</pre>
  
 
Example:
 
Example:
 +
<pre>
 
  # Hide real floppy drive (when no real floppy drive is attached)
 
  # Hide real floppy drive (when no real floppy drive is attached)
 
  LABEL hide_floppy
 
  LABEL hide_floppy
Line 250: Line 281:
 
   INITRD hdt.img
 
   INITRD hdt.img
 
   APPEND nopass
 
   APPEND nopass
 +
</pre>
  
 
+
==Enable/Disable BIOS Enhanced Disk Drive Services==
===Enable/Disable BIOS Enhanced Disk Drive Services===
+
 
MEMDISK by default supports EDD/EBIOS on hard disks, but not on floppy disks.  This can be controlled with the options:
 
MEMDISK by default supports EDD/EBIOS on hard disks, but not on floppy disks.  This can be controlled with the options:
  
Line 259: Line 290:
 
</pre>
 
</pre>
 
Example:
 
Example:
 +
<pre>
 
  # Enable EDD for the HDT floppy
 
  # Enable EDD for the HDT floppy
 
  LABEL EDD_on_floppy
 
  LABEL EDD_on_floppy
Line 264: Line 296:
 
   INITRD hdt.img
 
   INITRD hdt.img
 
   APPEND edd
 
   APPEND edd
 +
</pre>
  
===MEMDISK and PXE booting===
+
==MEMDISK and PXE booting==
 
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]
 
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]
  
 +
<pre>
 
   keeppxe      Keep PXE capabilities when booted from PXELINUX
 
   keeppxe      Keep PXE capabilities when booted from PXELINUX
 +
</pre>
  
 
+
==Pause MEMDISK before booting==
===Pause MEMDISK before booting===
+
 
To view the messages produced by MEMDISK, use:
 
To view the messages produced by MEMDISK, use:
  
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Example:
 
Example:
 +
<pre>
 
  # Pause MEMDISK before booting
 
  # Pause MEMDISK before booting
 
  LABEL pause_memdisk
 
  LABEL pause_memdisk
Line 282: Line 317:
 
   INITRD hdt.img
 
   INITRD hdt.img
 
   APPEND pause
 
   APPEND pause
 +
</pre>
  
 
+
==Set stack size==
===Set stack size===
+
 
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:
 
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:
  
Line 290: Line 325:
  
 
Example:
 
Example:
 +
<pre>
 
  # Change stack size to 2kiB (2048 bytes)
 
  # Change stack size to 2kiB (2048 bytes)
 
  LABEL change_stack_size
 
  LABEL change_stack_size
Line 295: Line 331:
 
   INITRD hdt.img
 
   INITRD hdt.img
 
   APPEND stack=2048
 
   APPEND stack=2048
 +
</pre>
  
==MEMDISK and generic El Torito CD-ROM driver for DOS==
+
=MEMDISK and generic El Torito CD-ROM driver for DOS=
 
If you're using MEMDISK to boot DOS from a CD-ROM (using ISOLINUX), you might find the '''generic El Torito CD-ROM driver (eltorito.sys)''' 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.
 
If you're using MEMDISK to boot DOS from a CD-ROM (using ISOLINUX), you might find the '''generic El Torito CD-ROM driver (eltorito.sys)''' 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.
  
Line 310: Line 347:
  
  
==Accessing MEMDISK arguments from DOS==
+
=Accessing MEMDISK arguments from DOS=
 
Many times it is very useful to be able to access the command line arguments given to MEMDISK from within the DOS image. This would allow one to combine several DOS images into one, by executing different scripts depending on the arguments.
 
Many times it is very useful to be able to access the command line arguments given to MEMDISK from within the DOS image. This would allow one to combine several DOS images into one, by executing different scripts depending on the arguments.
  

Revision as of 20:45, 7 July 2010


What is MEMDISK?

MEMDISK is meant to allow booting legacy operating systems. MEMDISK can boot floppy images, hard disk images and some ISO images.

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.


How can I use MEMDISK?

MEMDISK is an auxiliary module used in conjunction with a boot loader that can load linux kernels (EXTLINUX/ISOLINUX/PXELINUX/SYSLINUX, grub, grub4dos grub2, ...). You need a disk image as well as the memdisk file itself. As far as the bootloader is concerned, MEMDISK is the "kernel" and disk image is the initial ramdisk (initrd).

The disk image, passed as initrd, can be a compressed zip or gzip file.

In the next examples hdt.img is a floppy image (hdt.iso is a ISO image) containing Hardware Detection Tool (runs directly on SYSLINUX) and dosboot.img is a floppy image that contains some version of DOS.


EXTLINUX/ISOLINUX/PXELINUX/SYSLINUX

You can use MEMDISK straight off the boot loader command line like the following:

memdisk initrd=hdt.img

... where, of course, hdt.img is the name of the disk image file. The memdisk file and the disk image need to be present in the appropriate location (for PXELINUX, on your TFTP server, for ISOLINUX, in the /isolinux directory on your CD, etc.)

Normally, however, you would put something like following in the configuration file:

 # Boot Hardware Detection Tool from floppy image
 LABEL hdt_floppy
  LINUX memdisk
  INITRD hdt.img

 # Boot Hardware Detection Tool from iso image (with 'iso' parameter)
 LABEL hdt_iso
  LINUX memdisk
  INITRD hdt.iso
  APPEND iso

 # Boot DOS from floppy image (with 'raw' parameter)
 LABEL dos_floppy_with_raw
  LINUX memdisk
  INITRD dosboot.img
  APPEND raw

GRUB and GRUB4DOS

In your menu.lst file, use something like:

 title Boot Hardware Detection Tool from floppy
   kernel /memdisk
   initrd /hdt.img

 title Boot Hardware Detection Tool from iso image (with 'iso' parameter)
   kernel /memdisk iso
   initrd /hdt.iso

 title Boot DOS from floppy image (with 'raw' parameter)
   kernel /memdisk raw
   initrd /dosboot.img

GRUB2

Add the following in your config scripts for grub2:

 menuentry "Boot Hardware Detection Tool from floppy" {
   linux16 /memdisk
   initrd16 /hdt.img
 }

 menuentry "Boot Hardware Detection Tool from iso" {
   linux16 /memdisk iso
   initrd16 /hdt.iso
 }

 menuentry "Boot DOS from floppy image (with 'raw' parameter)" {
   linux16 /memdisk raw
   initrd16 /dosboot.img
 }

Supported image types

The image file should contain a disk image, either a floppy disk or hard disk image, or an iso image.

The disk image can be compressed with zip or gzip.


Floppy images

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.

 LABEL floppy_image
  LINUX memdisk
  INITRD floppy.img

If your image is larger than 4 MB and a floppy image, you can force MEMDISK to treat it as a floppy image:

 LABEL floppy_image
  LINUX memdisk
  INITRD floppy.img
  APPEND floppy

Hard disk images

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.)

 LABEL harddisk_image
  LINUX memdisk
  INITRD harddisk.img

If your image is smaller than 4 MB and it is a hard disk image, you can force MEMDISK to treat it as a hard disk image:

 LABEL harddisk_image
  LINUX memdisk
  INITRD harddisk.img
  APPEND harddisk

ISO images

For ISO images, the parameter 'iso' must be passed to MEMDISK.

 LABEL hdt_iso
   LINUX memdisk
   INITRD hdt.iso
   APPEND iso

Sometimes

  APPEND iso raw

is the better "APPEND" option.

It is possible to map and boot from some CD/DVD images using MEMDISK. No-emulation, floppy emulation and hard disk emulation ISO's are supported. "The "map" process is implemented using INT 13 - any disk emulation will remain accessible from an OS that uses compatible mode disk access, e.g. DOS and Windows 9x. The emulation via INT13 can't however, be accessed from an OS which uses protected mode drivers (Windows NT/2000/XP/2003/Vista/2008/7, Linux, FreeBSD) once the protected mode kernel drivers take control.


INT13 access: Not all images will boot completely!

Real mode operating systems and boot loaders that use INT13 BIOS calls

DOS (MS-DOS, FreeDOS, DR-DOS, ...), Windows 95/98/ME and boot loaders (Syslinux, grub, grub4dos, gujin, gag, mbldr, ...) that use INT13 to read from disks will boot completely with MEMDISK (assuming that there are no BIOS bugs, or software bugs).

Windows NT/2000/XP/2003/Vista/2008/7 (NT based)

These Windows versions use INT13 access only in the start of the booting process (loading only the necessary drivers). Once the protected mode drivers are functional to access the disks, Windows can't see the memory mapped drives created by MEMDISK (CD/DVD, hard disk and floppy disk images) and it will fail to boot completely.


Solutions:

- WinVBlock driver

WinVBlock is a Windows driver that overcomes this problem. It detects the MEMDISK mapped drives (CD/DVD, hard disk and floppy disk images) so Windows can read and write to those disks.

http://www.boot-land.net/forums/index.php?showtopic=8168

It will require the 'raw' parameter on some PCs.

 LABEL windows_winvblock
   LINUX memdisk
   INITRD windows_harddisk.img
   APPEND raw

- Windows PE based

You can also build a RAM disk based Windows PE. RAM disk based discs include Windows PE 2/2.1 and builds that utilize ramdisk.sys and setupldr.bin files from windows 2003 server SP1 source; see

- Windows Vista/2008/7 with WIM images

Windows Vista/2008/7 can be booted from a WIM image (loaded from disk via INT13).

Linux

The majority of Linux based CD images will also fail to work with MEMDISK ISO emulation. Linux distributions require kernel and initrd files to be specified, as soon as these files are loaded the protected mode kernel driver(s) take control and the virtual CD will no longer be accessible. If any other files are required from the CD/DVD they will be missing, resulting in boot error(s).

Linux distributions that only require kernel and initrd files function fully via ISO emulation, as no other data needs accessing from the virtual CD/DVD drive once they have been loaded. The boot loader has read all necessary files to memory by using INT 13, before booting the kernel.


Parameters and options

Specifying geometry and image type manually

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.

Example:

 # Boot harddisk image as second hard disk and specify C/H/S geometry
 LABEL hdt_floppy
   LINUX memdisk
   INITRD harddisk.img
   APPEND harddisk=1 c=255 h=64 s=22

Set memory access method (raw, bigraw, int , safeint)

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.

It is possible that your image works fine without those parameters on some PCs or virtual machines, but fail to boot on other PCs. In this situation, adding 'raw' will normally solve your problem.

Example:

 LABEL dos_with_extended_memory_manager
   LINUX memdisk
   INITRD dos_emm.img
   APPEND raw

Write protected floppy and hard disk images

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

Example:

 # Simulate write protected floppy
 LABEL hdt_write_protected_floppy
   LINUX memdisk
   INITRD hdt.img
   APPEND ro

Hide real floppy or hard drive

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:

   nopass       Hide all real drives of the same type (floppy or hard disk)
   nopassany    Hide all real drives (floppy and hard disk)

Example:

 # Hide real floppy drive (when no real floppy drive is attached)
 LABEL hide_floppy
   LINUX memdisk
   INITRD hdt.img
   APPEND nopass

Enable/Disable BIOS Enhanced Disk Drive Services

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

Example:

 # Enable EDD for the HDT floppy
 LABEL EDD_on_floppy
   LINUX memdisk
   INITRD hdt.img
   APPEND edd

MEMDISK and PXE booting

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: [1]

   keeppxe      Keep PXE capabilities when booted from PXELINUX

Pause MEMDISK before booting

To view the messages produced by MEMDISK, use:

  pause        Wait for a keypress right before booting

Example:

 # Pause MEMDISK before booting
 LABEL pause_memdisk
   LINUX memdisk
   INITRD hdt.img
   APPEND pause

Set stack size

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

Example:

 # Change stack size to 2kiB (2048 bytes)
 LABEL change_stack_size
   LINUX memdisk
   INITRD hdt.img
   APPEND stack=2048

MEMDISK and generic El Torito CD-ROM driver for DOS

If you're using MEMDISK to boot DOS from a CD-ROM (using ISOLINUX), you might find the generic El Torito CD-ROM driver (eltorito.sys) 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.

Example usage of eltorito.sys in CONFIG.SYS:

device=eltorito.sys /X:MSCD0001

Corresponding MSCDEX command which can be placed in AUTOEXEC.BAT:

MSCDEX /X:MSCD0001 /L:X

Where X is the drive letter.


Accessing MEMDISK arguments from DOS

Many times it is very useful to be able to access the command line arguments given to MEMDISK from within the DOS image. This would allow one to combine several DOS images into one, by executing different scripts depending on the arguments.

You can use 3 different programs to get the those arguments:

  • mdiskchk.com (not the Syslinux one), enhanced by Shao Miller:
 http://git.etherboot.org/?p=people/sha0/syslinux.git;a=commit;h=44fb149957ce0b0848f6a51ea900842b8f06519f
  • getargs.com written by Eric Auer (also can check for the existence of drives):
 http://ericauer.cosmodata.virtuaserver.com.br/soft/specials/combined-drivecheck-memdisk-getargs.zip
  • getargs.com written by Murali krishnan Ganapathy:
 http://people.cs.uchicago.edu/~gmurali/gui/downloads.html

Add one of the getargs.com versions to your DOS image and use it as follows inside any of your .bat files:

REM Retrieve and save MEMDISK arguments in settings.bat
getargs.com > settings.bat

REM Run setting.bat so the retreived MEMDISK arguments are
REM set as environment variables for further usage.
settings.bat

If the call to MEMDISK was:

# Boot DOS and pass arguments
LABEL dos_with_args
LINUX memdisk
INITRD my_dos.img
APPEND ACTION=install NETSHARE=sharename

then after the call to settings.bat the environment variables INITRD, ACTION and NETSHARE will be set to my_dos.img, install and sharename respectively.

The tool mdiskchk.com (dosutil/mdiskchk.com) can display more info about MEMDISK from DOS.