diff --git a/Visual Studio Projects/AltairZ80.vcproj b/Visual Studio Projects/AltairZ80.vcproj
index 5fb8f139..79621617 100644
--- a/Visual Studio Projects/AltairZ80.vcproj	
+++ b/Visual Studio Projects/AltairZ80.vcproj	
@@ -41,7 +41,7 @@
 				Name="VCCLCompilerTool"
 				Optimization="0"
 				AdditionalIncludeDirectories="../AltairZ80/;./;../;../slirp;../slirp_glue;../slirp_glue/qemu;../slirp_glue/qemu/win32/include;../../windows-build/include;;../../windows-build/include/SDL2"
-				PreprocessorDefinitions="USE_SIM_IMD;NO_INLINE;SIM_BUILD_TOOL=simh-Visual-Studio-Project;_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS;_WINSOCK_DEPRECATED_NO_WARNINGS;SIM_NEED_GIT_COMMIT_ID;HAVE_PCRE_H;PCRE_STATIC"
+				PreprocessorDefinitions="NO_INLINE;SIM_BUILD_TOOL=simh-Visual-Studio-Project;_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS;_WINSOCK_DEPRECATED_NO_WARNINGS;SIM_NEED_GIT_COMMIT_ID;HAVE_PCRE_H;PCRE_STATIC"
 				KeepComments="false"
 				BasicRuntimeChecks="0"
 				RuntimeLibrary="1"
@@ -125,7 +125,7 @@
 				OmitFramePointers="true"
 				WholeProgramOptimization="true"
 				AdditionalIncludeDirectories="../AltairZ80/;./;../;../slirp;../slirp_glue;../slirp_glue/qemu;../slirp_glue/qemu/win32/include;../../windows-build/include;;../../windows-build/include/SDL2"
-				PreprocessorDefinitions="USE_SIM_IMD;NO_INLINE;SIM_BUILD_TOOL=simh-Visual-Studio-Project;_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS;_WINSOCK_DEPRECATED_NO_WARNINGS;SIM_NEED_GIT_COMMIT_ID;HAVE_PCRE_H;PCRE_STATIC"
+				PreprocessorDefinitions="NO_INLINE;SIM_BUILD_TOOL=simh-Visual-Studio-Project;_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS;_WINSOCK_DEPRECATED_NO_WARNINGS;SIM_NEED_GIT_COMMIT_ID;HAVE_PCRE_H;PCRE_STATIC"
 				StringPooling="true"
 				RuntimeLibrary="0"
 				EnableFunctionLevelLinking="true"
diff --git a/Visual Studio Projects/PDQ3.vcproj b/Visual Studio Projects/PDQ3.vcproj
index c5cf1cea..36b7f57a 100644
--- a/Visual Studio Projects/PDQ3.vcproj	
+++ b/Visual Studio Projects/PDQ3.vcproj	
@@ -41,7 +41,7 @@
 				Name="VCCLCompilerTool"
 				Optimization="0"
 				AdditionalIncludeDirectories="./;../;../slirp;../slirp_glue;../slirp_glue/qemu;../slirp_glue/qemu/win32/include;../../windows-build/include;;../../windows-build/include/SDL2"
-				PreprocessorDefinitions="USE_SIM_IMD;SIM_BUILD_TOOL=simh-Visual-Studio-Project;_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS;_WINSOCK_DEPRECATED_NO_WARNINGS;SIM_NEED_GIT_COMMIT_ID;HAVE_PCRE_H;PCRE_STATIC"
+				PreprocessorDefinitions="SIM_BUILD_TOOL=simh-Visual-Studio-Project;_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS;_WINSOCK_DEPRECATED_NO_WARNINGS;SIM_NEED_GIT_COMMIT_ID;HAVE_PCRE_H;PCRE_STATIC"
 				KeepComments="false"
 				BasicRuntimeChecks="0"
 				RuntimeLibrary="1"
@@ -125,7 +125,7 @@
 				OmitFramePointers="true"
 				WholeProgramOptimization="true"
 				AdditionalIncludeDirectories="./;../;../slirp;../slirp_glue;../slirp_glue/qemu;../slirp_glue/qemu/win32/include;../../windows-build/include;;../../windows-build/include/SDL2"
-				PreprocessorDefinitions="USE_SIM_IMD;SIM_BUILD_TOOL=simh-Visual-Studio-Project;_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS;_WINSOCK_DEPRECATED_NO_WARNINGS;SIM_NEED_GIT_COMMIT_ID;HAVE_PCRE_H;PCRE_STATIC"
+				PreprocessorDefinitions="SIM_BUILD_TOOL=simh-Visual-Studio-Project;_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS;_WINSOCK_DEPRECATED_NO_WARNINGS;SIM_NEED_GIT_COMMIT_ID;HAVE_PCRE_H;PCRE_STATIC"
 				StringPooling="true"
 				RuntimeLibrary="0"
 				EnableFunctionLevelLinking="true"
diff --git a/Visual Studio Projects/SAGE.vcproj b/Visual Studio Projects/SAGE.vcproj
index f61a11d8..5cf7d520 100644
--- a/Visual Studio Projects/SAGE.vcproj	
+++ b/Visual Studio Projects/SAGE.vcproj	
@@ -41,7 +41,7 @@
 				Name="VCCLCompilerTool"
 				Optimization="0"
 				AdditionalIncludeDirectories="./;../;../slirp;../slirp_glue;../slirp_glue/qemu;../slirp_glue/qemu/win32/include;../../windows-build/include;;../../windows-build/include/SDL2"
-				PreprocessorDefinitions="HAVE_INT64;USE_SIM_IMD;SIM_BUILD_TOOL=simh-Visual-Studio-Project;_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS;_WINSOCK_DEPRECATED_NO_WARNINGS;SIM_NEED_GIT_COMMIT_ID;HAVE_PCRE_H;PCRE_STATIC"
+				PreprocessorDefinitions="HAVE_INT64;SIM_BUILD_TOOL=simh-Visual-Studio-Project;_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS;_WINSOCK_DEPRECATED_NO_WARNINGS;SIM_NEED_GIT_COMMIT_ID;HAVE_PCRE_H;PCRE_STATIC"
 				KeepComments="false"
 				BasicRuntimeChecks="0"
 				RuntimeLibrary="1"
@@ -127,7 +127,7 @@
 				OmitFramePointers="true"
 				WholeProgramOptimization="true"
 				AdditionalIncludeDirectories="./;../;../slirp;../slirp_glue;../slirp_glue/qemu;../slirp_glue/qemu/win32/include;../../windows-build/include;;../../windows-build/include/SDL2"
-				PreprocessorDefinitions="HAVE_INT64;USE_SIM_IMD;SIM_BUILD_TOOL=simh-Visual-Studio-Project;_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS;_WINSOCK_DEPRECATED_NO_WARNINGS;SIM_NEED_GIT_COMMIT_ID;HAVE_PCRE_H;PCRE_STATIC"
+				PreprocessorDefinitions="HAVE_INT64;SIM_BUILD_TOOL=simh-Visual-Studio-Project;_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS;_WINSOCK_DEPRECATED_NO_WARNINGS;SIM_NEED_GIT_COMMIT_ID;HAVE_PCRE_H;PCRE_STATIC"
 				StringPooling="true"
 				RuntimeLibrary="0"
 				EnableFunctionLevelLinking="true"
diff --git a/descrip.mms b/descrip.mms
index b7c00d6f..07d666ea 100644
--- a/descrip.mms
+++ b/descrip.mms
@@ -371,7 +371,7 @@ ALTAIRZ80_SOURCE2 = $(ALTAIRZ80_DIR)S100_DISK1A.C,$(ALTAIRZ80_DIR)S100_DISK2.C,\
                     $(ALTAIRZ80_DIR)M68KCPU.C,$(ALTAIRZ80_DIR)M68KDASM.C,\
                     $(ALTAIRZ80_DIR)M68KOPAC.C,$(ALTAIRZ80_DIR)M68KOPDM.C,\
                     $(ALTAIRZ80_DIR)M68KOPNZ.C,$(ALTAIRZ80_DIR)M68KOPS.C,$(ALTAIRZ80_DIR)M68KSIM.C
-ALTAIRZ80_OPTIONS = /INCL=($(SIMH_DIR),$(ALTAIRZ80_DIR))/DEF=($(CC_DEFS),"USE_SIM_IMD=1")
+ALTAIRZ80_OPTIONS = /INCL=($(SIMH_DIR),$(ALTAIRZ80_DIR))/DEF=($(CC_DEFS))
 
 #
 # Data General Nova Simulator Definitions.
diff --git a/makefile b/makefile
index 0d539848..1d2c7a08 100644
--- a/makefile
+++ b/makefile
@@ -1762,7 +1762,7 @@ ALTAIRZ80 = ${ALTAIRZ80D}/altairz80_cpu.c ${ALTAIRZ80D}/altairz80_cpu_nommu.c \
 	${ALTAIRZ80D}/m68kcpu.c ${ALTAIRZ80D}/m68kdasm.c ${ALTAIRZ80D}/m68kasm.c \
 	${ALTAIRZ80D}/m68kopac.c ${ALTAIRZ80D}/m68kopdm.c \
 	${ALTAIRZ80D}/m68kopnz.c ${ALTAIRZ80D}/m68kops.c ${ALTAIRZ80D}/m68ksim.c
-ALTAIRZ80_OPT = -I ${ALTAIRZ80D} -DUSE_SIM_IMD
+ALTAIRZ80_OPT = -I ${ALTAIRZ80D}
 
 
 GRID = ${SIMHD}/GRI
@@ -2142,12 +2142,12 @@ SAGE = ${SAGED}/sage_cpu.c ${SAGED}/sage_sys.c ${SAGED}/sage_stddev.c \
     ${SAGED}/m68k_cpu.c ${SAGED}/m68k_mem.c ${SAGED}/m68k_scp.c \
     ${SAGED}/m68k_parse.tab.c ${SAGED}/m68k_sys.c \
     ${SAGED}/i8251.c ${SAGED}/i8253.c ${SAGED}/i8255.c ${SAGED}/i8259.c ${SAGED}/i8272.c 
-SAGE_OPT = -I ${SAGED} -DHAVE_INT64 -DUSE_SIM_IMD
+SAGE_OPT = -I ${SAGED} -DHAVE_INT64
 
 PDQ3D = ${SIMHD}/PDQ-3
 PDQ3 = ${PDQ3D}/pdq3_cpu.c ${PDQ3D}/pdq3_sys.c ${PDQ3D}/pdq3_stddev.c \
     ${PDQ3D}/pdq3_mem.c ${PDQ3D}/pdq3_debug.c ${PDQ3D}/pdq3_fdc.c 
-PDQ3_OPT = -I ${PDQ3D} -DUSE_SIM_IMD
+PDQ3_OPT = -I ${PDQ3D}
 
 #
 # Build everything (not the unsupported/incomplete or experimental simulators)
diff --git a/sim_defs.h b/sim_defs.h
index a97492e5..6beb2146 100644
--- a/sim_defs.h
+++ b/sim_defs.h
@@ -152,6 +152,10 @@ extern int sim_vax_snprintf(char *buf, size_t buf_size, const char *fmt, ...);
 #define USE_REGEX 1
 #endif
 
+#if (defined (__MWERKS__) && defined (macintosh)) || defined(__DECC)
+#define __FUNCTION__ __FILE__
+#endif
+
 #ifdef  __cplusplus
 extern "C" {
 #endif
@@ -592,6 +596,7 @@ struct UNIT {
     void                *up8;                           /* device specific */
     uint16              us9;                            /* device specific */
     uint16              us10;                           /* device specific */
+    uint32              disk_type;                      /* Disk specific info */
     void                *tmxr;                          /* TMXR linkage */
     uint32              recsize;                        /* Tape specific info */
     t_addr              tape_eom;                       /* Tape specific info */
diff --git a/sim_imd.c b/sim_imd.c
index 0710332e..9d045c31 100644
--- a/sim_imd.c
+++ b/sim_imd.c
@@ -41,15 +41,9 @@
                     Cylinder maps in the .IMD image file (AGN)
 */
 
-#if defined(USE_SIM_IMD)
-
 #include "sim_defs.h"
 #include "sim_imd.h"
 
-#if (defined (__MWERKS__) && defined (macintosh)) || defined(__DECC)
-#define __FUNCTION__ __FILE__
-#endif
-
 static t_stat commentParse(DISK_INFO *myDisk, uint8 comment[], uint32 buffLen);
 static t_stat diskParse(DISK_INFO *myDisk, uint32 isVerbose);
 static t_stat diskFormat(DISK_INFO *myDisk);
@@ -85,7 +79,7 @@ DISK_INFO *diskOpen(FILE *fileref, uint32 isVerbose)
  * After this function returns, the file pointer is placed after the comment and
  * the 0x1A "EOF" marker.
  *
- * The comment parameter is optional, and if NULL, then the ocmment will not
+ * The comment parameter is optional, and if NULL, then the comment will not
  * be extracted from the IMD file, but the file position will still be advanced
  * to the end of the comment.
  */
@@ -788,5 +782,3 @@ t_stat assignDiskType(UNIT *uptr) {
     sim_fseeko(uptr->fileref, pos, SEEK_SET);
     return result;
 }
-
-#endif /* USE_SIM_IMD */
diff --git a/sim_imd.h b/sim_imd.h
index d4142105..0b311bfc 100644
--- a/sim_imd.h
+++ b/sim_imd.h
@@ -39,10 +39,6 @@
 #ifndef SIM_IMD_H_
 #define SIM_IMD_H_     0
 
-#if !defined(USE_SIM_IMD)
-#error This simulator must be compiled with USE_SIM_IMD defined
-#else
-
 #include "sim_defs.h"
 
 typedef struct {
@@ -137,6 +133,4 @@ extern t_stat trackWrite(DISK_INFO *myDisk,
                uint32 *flags);
 extern t_stat assignDiskType(UNIT *uptr);
 
-#endif /* USE_SIM_IMD */
-
 #endif