now that the user has the option to set the MCB starting segment,

make the dynamic kernel alloc default 0x70 for better compatibility with
DOS games, but recommend 0x51 for people who want to eke out more
conventional memory.

src/dos/dos.cpp

@@ -1643,7 +1643,7 @@ class DOS:public Module_base{
 			else if (private_always_from_umb) {
 				DOS_GetMemory_Choose(); /* the pool starts in UMB */
 				if (minimum_mcb_segment == 0)
-					DOS_MEM_START = 0x51; /* and we allow allocation from down below where the DOS kernel *would* reside */
+					DOS_MEM_START = 0x70;
 				else
 					DOS_MEM_START = minimum_mcb_segment;
 

src/dosbox.cpp

@@ -1730,8 +1730,10 @@ void DOSBOX_Init(void) {
 	Pbool->Set_help("Enable XMS support.");
 
 	Phex = secprop->Add_hex("minimum mcb segment", Property::Changeable::WhenIdle,0);
-	Phex->Set_help("Minimum segment value to begin memory allocation from. Set to 0 for default.\n"
-			"There may be compatibility issues if this value is below 0x70.");
+	Phex->Set_help("Minimum segment value to begin memory allocation from, in hexadecimal. Set to 0 for default.\n"
+			"Recommended value is 70, some DOS games have problems if the value is lower than that.\n"
+			"The lowest value you can safely use is 51, any value lower than that risks conflict with\n"
+			"the BIOS data area and interrupt vector table.");
 
 	Pbool = secprop->Add_bool("enable dummy device mcb",Property::Changeable::OnlyAtStart,true);
 	Pbool->Set_help("If set (default), allocate a fake device MCB at the base of conventional memory.\n"