diff --git a/src/mame/drivers/mediagx.cpp b/src/mame/drivers/mediagx.cpp
index cd40dea7e17..383330544a7 100644
--- a/src/mame/drivers/mediagx.cpp
+++ b/src/mame/drivers/mediagx.cpp
@@ -1010,6 +1010,8 @@ ROM_START( a51site4 )
 	ROMX_LOAD("a51s4_bios_09-15-98.u1", 0x00000, 0x40000, CRC(f8cd6a6b) SHA1(75f851ae21517b729a5596ce5e042ebfaac51778), ROM_BIOS(1)) /* Build date 09/15/98 string stored at 0x3fff5 */
 	ROM_SYSTEM_BIOS(1, "old", "v1.0f" )
 	ROMX_LOAD("a51s4_bios_07-11-98.u1", 0x00000, 0x40000, CRC(5ee189cc) SHA1(0b0d9321a4c59b1deea6854923e655a4d8c4fcfe), ROM_BIOS(2)) /* Build date 07/11/98 string stored at 0x3fff5 */
+	ROM_SYSTEM_BIOS(2, "older", "v1.0d" ) /* doesn't work with the HDs currently available, shows "FOR EVALUATION ONLY" */
+	ROMX_LOAD("a51s4_bios_04-22-98.u1", 0x00000, 0x40000, CRC(2008bfc6) SHA1(004bec8759fb04d375c6efc49d048693d1f871ee), ROM_BIOS(3)) /* Build date 04/22/98 string stored at 0x3fff5 */
 
 	ROM_REGION(0x08100, "gfx1", 0)
 	ROM_LOAD("cga.chr",     0x00000, 0x01000, CRC(42009069) SHA1(ed08559ce2d7f97f68b9f540bddad5b6295294dd))
@@ -1024,6 +1026,8 @@ ROM_START( a51site4a ) /* When dumped connected straight to IDE the cylinders we
 	ROMX_LOAD("a51s4_bios_09-15-98.u1", 0x00000, 0x40000, CRC(f8cd6a6b) SHA1(75f851ae21517b729a5596ce5e042ebfaac51778), ROM_BIOS(1)) /* Build date 09/15/98 string stored at 0x3fff5 */
 	ROM_SYSTEM_BIOS(1, "old", "v1.0f" )
 	ROMX_LOAD("a51s4_bios_07-11-98.u1", 0x00000, 0x40000, CRC(5ee189cc) SHA1(0b0d9321a4c59b1deea6854923e655a4d8c4fcfe), ROM_BIOS(2)) /* Build date 07/11/98 string stored at 0x3fff5 */
+	ROM_SYSTEM_BIOS(2, "older", "v1.0d" ) /* doesn't work with the HDs currently available, shows "FOR EVALUATION ONLY" */
+	ROMX_LOAD("a51s4_bios_04-22-98.u1", 0x00000, 0x40000, CRC(2008bfc6) SHA1(004bec8759fb04d375c6efc49d048693d1f871ee), ROM_BIOS(3)) /* Build date 04/22/98 string stored at 0x3fff5, doesn't work */
 
 	ROM_REGION(0x08100, "gfx1", 0)
 	ROM_LOAD("cga.chr",     0x00000, 0x01000, CRC(42009069) SHA1(ed08559ce2d7f97f68b9f540bddad5b6295294dd))