diff options
authorH. Peter Anvin <hpa@zytor.com>2008-07-03 15:29:57 -0700
committerH. Peter Anvin <hpa@zytor.com>2008-07-03 15:29:57 -0700
commitfb75c40b2d119afcef002cb66d359536ad576ff6 (patch)
parent8e5db045c60ce25a9eb65a1803d47be4002a3e17 (diff)
doc/memdisk.txt: document INT 1Eh fields
Document the fields to recover the original INT 1Eh vector.
1 files changed, 12 insertions, 5 deletions
diff --git a/doc/memdisk.txt b/doc/memdisk.txt
index 304de52b..34a85406 100644
--- a/doc/memdisk.txt
+++ b/doc/memdisk.txt
@@ -161,7 +161,7 @@ http://www.ctyme.com/rbrown.htm, for a detailed description.
The MEMDISK info structure currently contains:
- [ES:DI] word Total size of structure (currently 28 bytes)
+ [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
@@ -171,9 +171,15 @@ The MEMDISK info structure currently contains:
[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 Currently unused
+ [ES:DI+28] word If nonzero, offset (vs ES) to installed DPT
+ This pointer+16 contains the original INT 1Eh
-MEMDISK 3.00 and higher has the size of this structure as 27; earlier
-versions had size 26 and did not include the boot loader ID.
+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]:
@@ -185,8 +191,9 @@ 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):
+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