diff --git a/src/mame/drivers/rmnimbus.cpp b/src/mame/drivers/rmnimbus.cpp
index 11b56579d81..d07492a7809 100644
--- a/src/mame/drivers/rmnimbus.cpp
+++ b/src/mame/drivers/rmnimbus.cpp
@@ -212,21 +212,40 @@ void rmnimbus_state::nimbus(machine_config &config)
 	SOFTWARE_LIST(config, "disk_list").set_original("nimbus");
 }
 
-
+/*
+Known unavailable BIOS set:
+	Another version of v1.31a labelled: SYS1 16128 31/10/86, SYS2 16129 28/10/86
+	Another version of v1.32c labelled: SYS1 17130 10.03.87, SYS 2. 17131 09.03.87
+	Another version of v1.32c labelled: SYS 1 21323 2/12/88, SYS 2 21324 5/1/89
+	v1.33c labelled "RESEARCH MACHINE P.N. 32857(32858) PC186 SYS1(SYS2) V1.33C", no date labelled
+	Another version of v1.40d labelled: 24693 IC30 02/7/91(AA), 24694 IC27 28/6/91(AA)
+*/
 ROM_START( nimbus )
 	ROM_REGION( 0x100000, MAINCPU_TAG, 0 )
 
-	ROM_SYSTEM_BIOS(0, "v131a", "Nimbus BIOS v1.31a (1986-06-18)")
-	ROMX_LOAD("sys1-1.31a-16128-1986-06-18.rom", 0xf0001, 0x8000, CRC(6416eb05) SHA1(1b640163a7efbc24381c7b24976a8609c066959b), ROM_SKIP(1) | ROM_BIOS(0))
-	ROMX_LOAD("sys2-1.31a-16129-1986-06-18.rom", 0xf0000, 0x8000, CRC(b224359d) SHA1(456bbe37afcd4429cca76ba2d6bd534dfda3fc9c), ROM_SKIP(1) | ROM_BIOS(0))
+	ROM_SYSTEM_BIOS(0, "v125a", "Nimbus BIOS v1.25a (1985-12-02)")
+	ROMX_LOAD("sys1-1.25a_13484_6-11-85_m5m27256p.rom", 0xf0001, 0x8000, CRC(5870df28) SHA1(12e1a7d22439d512b221c355d641d113f0e6568e), ROM_SKIP(1) | ROM_BIOS(0))
+	ROMX_LOAD("sys2-1.25a_13485_2-12-85_m5m27256p.rom", 0xf0000, 0x8000, CRC(15888320) SHA1(32cc2485468c6a9944e505162e319a283eef8a84), ROM_SKIP(1) | ROM_BIOS(0))
+	
+	ROM_SYSTEM_BIOS(1, "v131a", "Nimbus BIOS v1.31a (1986-06-18)")
+	ROMX_LOAD("sys1-1.31a-16128-1986-06-18.rom", 0xf0001, 0x8000, CRC(6416eb05) SHA1(1b640163a7efbc24381c7b24976a8609c066959b), ROM_SKIP(1) | ROM_BIOS(1))
+	ROMX_LOAD("sys2-1.31a-16129-1986-06-18.rom", 0xf0000, 0x8000, CRC(b224359d) SHA1(456bbe37afcd4429cca76ba2d6bd534dfda3fc9c), ROM_SKIP(1) | ROM_BIOS(1))
 
-	ROM_SYSTEM_BIOS(1, "v132f", "Nimbus BIOS v1.32f (1989-10-20)")
-	ROMX_LOAD("sys-1-1.32f-22779-1989-10-20.rom", 0xf0001, 0x8000, CRC(786c31e8) SHA1(da7f828f7f96087518bea1a3d89fee59b283b4ba), ROM_SKIP(1) | ROM_BIOS(1))
-	ROMX_LOAD("sys-2-1.32f-22779-1989-10-20.rom", 0xf0000, 0x8000, CRC(0be3db64) SHA1(af806405ec6fbc20385705f90d5059a47de17b08), ROM_SKIP(1) | ROM_BIOS(1))
+	ROM_SYSTEM_BIOS(2, "v132c", "Nimbus BIOS v1.32c (1987-03-21)")
+	ROMX_LOAD("sys1-1.32c_17130_21-3-87_m5m27256p_63210c.rom", 0xf0001, 0x8000, CRC(91b88b29) SHA1(1db5e3ff8bb237f006b53d5f91b080f99e95a58e), ROM_SKIP(1) | ROM_BIOS(2))
+	ROMX_LOAD("sys2-1.32c_17131_21-3-87_m5m27256p_63210c.rom", 0xf0000, 0x8000, CRC(4876cc4f) SHA1(4348b293f5c443453c08663809bfa5c462222137), ROM_SKIP(1) | ROM_BIOS(2))
 
-	ROM_SYSTEM_BIOS(2, "v140d", "Nimbus BIOS v1.40d (1990-xx-xx)")
-	ROMX_LOAD("sys-1-1.40d.rom", 0xf0001, 0x8000, CRC(b8d3dc0b) SHA1(82e0dcdc6c7a83339af68d6cb61211fcb14bed88), ROM_SKIP(1) | ROM_BIOS(2))
-	ROMX_LOAD("sys-2-1.40d.rom", 0xf0000, 0x8000, CRC(b0826b0b) SHA1(3baa369a0e7ef138ca29aae0ee8a89ab670a02b9), ROM_SKIP(1) | ROM_BIOS(2))
+	ROM_SYSTEM_BIOS(3, "v132d", "Nimbus BIOS v1.32d (1989-01-20)")
+	ROMX_LOAD("sys1-1.32d_21323_17-1-89_m5m27256p_63210c.rom", 0xf0001, 0x8000, CRC(e0ecbc02) SHA1(b5cb16df23bd30af5556660364e4733790f99164), ROM_SKIP(1) | ROM_BIOS(3))
+	ROMX_LOAD("sys2-1.32d_21324_20-1-89_m5m27256p_63210c.rom", 0xf0000, 0x8000, CRC(8ef4a357) SHA1(29309cb8bfe9256d4684f3e6575e3720b0dcacd4), ROM_SKIP(1) | ROM_BIOS(3))
+	
+	ROM_SYSTEM_BIOS(4, "v132f", "Nimbus BIOS v1.32f (1989-11-29)")
+	ROMX_LOAD("sys-1-1.32f-22779-1989-11-29.rom", 0xf0001, 0x8000, CRC(786c31e8) SHA1(da7f828f7f96087518bea1a3d89fee59b283b4ba), ROM_SKIP(1) | ROM_BIOS(4))
+	ROMX_LOAD("sys-2-1.32f-22778-1989-11-29.rom", 0xf0000, 0x8000, CRC(0be3db64) SHA1(af806405ec6fbc20385705f90d5059a47de17b08), ROM_SKIP(1) | ROM_BIOS(4))
+
+	ROM_SYSTEM_BIOS(5, "v140d", "Nimbus BIOS v1.40d (1990-02-19)")
+	ROMX_LOAD("rt-1.40d-24694-ic27-1990-02-19.rom", 0xf0001, 0x8000, CRC(b8d3dc0b) SHA1(82e0dcdc6c7a83339af68d6cb61211fcb14bed88), ROM_SKIP(1) | ROM_BIOS(5))
+	ROMX_LOAD("left-1.40d-24693-ic30-1990-02-15.rom", 0xf0000, 0x8000, CRC(b0826b0b) SHA1(3baa369a0e7ef138ca29aae0ee8a89ab670a02b9), ROM_SKIP(1) | ROM_BIOS(5))
 
 	ROM_REGION( 0x4000, IOCPU_TAG, 0 )
 	ROM_LOAD("hexec-v1.02u-13488-1985-10-29.rom", 0x0000, 0x1000, CRC(75c6adfd) SHA1(0f11e0b7386c6368d20e1fc7a6196d670f924825))