diff --git a/Doc/ChangeLog.txt b/Doc/ChangeLog.txt
index d2e2034c..a822c7f9 100644
--- a/Doc/ChangeLog.txt
+++ b/Doc/ChangeLog.txt
@@ -41,6 +41,7 @@ Version 3.5
 - MAP: Contributed COPYSL utility
 - MAP: Added new HBIOS function SYSGET_DIOMED
 - MAP: ROMLDR now uses SYSGET_DIOMED to get Slice Sector for boot
+- MAP: CBIOS now uses SYSGET_DIOMED during drive selection
 
 Version 3.4
 -----------
diff --git a/Source/CBIOS/cbios.asm b/Source/CBIOS/cbios.asm
index 782bac60..b1461f49 100644
--- a/Source/CBIOS/cbios.asm
+++ b/Source/CBIOS/cbios.asm
@@ -439,12 +439,12 @@ WBOOT:
 	LD	DE,(BNKBIOS)		; UBIOS_PAGE (SEE PAGES.INC)
 	RST	08			; DO IT
 	PUSH	DE			; SAVE PREVIOUS BANK
-	
+
 	LD	HL,(CCPBUF)		; ADDRESS OF CCP BUF IN BIOS MEM
 	LD	DE,CCP_LOC		; ADDRESS IN HI MEM OF CCP
 	LD	BC,CCP_SIZ		; SIZE OF CCP
 	LDIR				; DO IT
-	
+
 	LD	BC,$01FB		; UNA FUNC = SET BANK
 	POP	DE			; RECOVER OPERATING BANK
 	RST	08			; DO IT
@@ -804,7 +804,7 @@ WRITE:
 	LD	A,C
 	LD	(WRTYPE),A	; SAVE WRITE TYPE
 	LD	A,DOP_WRITE
-	JR	READWRITE
+	;JR	READWRITE	; OPTIMISATION (FALL THRU TO READWRITE)
 ;
 ;__________________________________________________________________________________________________
 READWRITE:
@@ -1232,11 +1232,11 @@ DSK_GETINF:
 	RLCA			; ... TO USE AS OFFSET INTO DRVMAP
 	CALL	ADDHLA		; ADD OFFSET
 	LD	D,(HL)		; D := UNIT
-	
+
 	LD	A,D		; PUT UNIT IN ACCUM
 	INC	A		; $FF -> $00
 	JR	Z,DSK_GETINF1	; HANDLE UNASSIGNED DRIVE LETTER
-	
+
 	INC	HL		; BUMP TO SLICE
 	LD	E,(HL)		; E := SLICE
 	INC	HL		; POINT TO DPH LSB
@@ -1261,7 +1261,8 @@ DSK_GETINF1:	; ERROR RETURN
 	INC	A
 	RET
 ;
-;
+; BIOS FUNCTION FOR SELECTING CPM DRIVE (A-P) IN C REGISTER
+; RETURN HL - BASE ADDRESS OF DPH (0x0000 FOR AN ERROR)
 ;
 DSK_SELECT:
 	LD	B,E		; SAVE E IN B FOR NOW
@@ -1321,19 +1322,8 @@ DSK_SELECT1A:
 	LD	(MEDID),A
 ;
 #ELSE
-;
-	; DETERMINE MEDIA IN DRIVE
-	LD	A,(SEKUNIT)	; GET UNIT
-	LD	C,A		; STORE IN C
-	LD	B,BF_DIOMEDIA	; DRIVER FUNCTION = DISK MEDIA
-	LD	E,1		; ENABLE MEDIA CHECK/DISCOVERY
-	RST	08		; DO IT
-	LD	A,E		; RESULTANT MEDIA ID TO ACCUM
-	LD	(MEDID),A	; SAVE IT
-	OR	A		; SET FLAGS
-	LD	HL,0		; ASSUME FAILURE
-	RET	Z		; BAIL OUT IF NO MEDIA
-;
+	; NOTE: Setting the (MEDID) is not required for RomWBW at this point
+	; The media ID is determined during call to DSK_MBR:
 #ENDIF
 ;
 	; CLEAR LBA OFFSET (DWORD)
@@ -1343,24 +1333,7 @@ DSK_SELECT1A:
 	SET	7,H		; ASSUME LBA ACCESS FOR NOW
 	LD	(SEKLBA+2),HL	; CLEAR SECOND WORD
 ;
-#IFDEF PLTWBW
-;
-	LD	A,(SEKUNIT)	; GET UNIT
-	LD	C,A		; STORE IN C
-	LD	B,BF_DIODEVICE	; HBIOS FUNC: REPORT DEVICE INFO
-	RST	08		; GET UNIT INFO, DEVICE TYPE IN D
-	LD	A,D		; DEVICE TYPE -> A
-	CP	DIODEV_FD	; FLOPPY?
-	JR	NZ,DSK_SELECT1B	; IF NOT, DO LBA IO
-	LD	HL,SEKLBA+3	; POINT TO HIGH ORDER BYTE
-	RES	7,(HL)		; SWITCH FROM LBA -> CHS
-;
-#ENDIF
-;
 DSK_SELECT1B:
-	; SET LEGACY SECTORS PER SLICE
-	LD	HL,16640	; LEGACY SECTORS PER SLICE
-	LD	(SPS),HL	; SAVE IT
 ;
 	; CHECK MBR OF PHYSICAL DISK BEING SELECTED
 	; WILL UPDATE MEDID AND LBAOFF IF VALID CP/M PARTITION EXISTS
@@ -1407,29 +1380,48 @@ DSK_SELECT2:
 ; THE MEDIA ID (MEDID).
 ;
 DSK_MBR:
+;
+#IFDEF PLTWBW
+;
+	; GET EXTENDED INFORMATION FOR THE DEVICE/SLICE
+	LD	A,(SEKUNIT)	; PASSING BOOT UNIT
+	LD	D,A
+	LD	A,(SLICE)	; AND SLICE
+	LD	E,A
+	LD	B,BF_SYSGET	; HBIOS FUNC: SYS GET
+	LD	C,BF_SYSGET_DIOMED ; HBIOS SUB-FUNC: GET DISK INFO
+	RST	08		; DO IT
+;
+	; CHECK ERRORS FROM THE FUNCTION
+	RET	NZ		; ABORT ON ERROR
+
+	; SAVE MEDIA ID
+	LD	A,C		; C IS MEDIA ID FROM HBIOS
+	LD	(MEDID),A	; SAVE IT
+
+	; TEST IF FLOPPY MEDIA - BIT 7 DEVICE ATTRIBUTES
+	BIT	7,B		; B IS ATTRIBUTES FROM HBIOS
+	JR	NZ,DSK_MBR11	; FLOPPY - SAVE AND RETURN DEHL -> CHS
+
+	; CODE FALL THRU NEXT IFDEF AND SETS 7,D
+	; THEN RETURNS DEHL -> LBA MODE
+;
+#ENDIF
+;
+#IFDEF PLTUNA
 	; CHECK MEDIA TYPE, ONLY HARD DISK IS APPLICABLE
 	LD	A,(MEDID)	; GET MEDIA ID
 	CP	MID_HD		; HARD DISK?
 	JR	Z,DSK_MBR0	; IF SO, CONTINUE
 	XOR	A		; ELSE, N/A, SIGNAL SUCCESS
 	RET			; AND RETURN
-	
+
 DSK_MBR0:
-;
-#IFDEF PLTWBW
-	; ACTIVATE BIOS BANK TO ACCESS DISK BUFFER
-	LD	(STKSAV),SP	; SAVE CUR STACK
-	LD	SP,STACK	; NEW STACK IN HI MEM
-	LD	A,(BNKBIOS)	; ACTIVATE HBIOS BANK
-	PUSH	IX		; SAVE IX
-	LD	IX,DSK_MBR1	; ROUTINE TO RUN
-	CALL	HB_BNKCALL	; DO IT
-	POP	IX		; RESTORE IX
-	LD	SP,(STKSAV)	; RESTORE ORIGINAL STACK
-	RET
-#ENDIF
-;
 DSK_MBR1:
+	; SET LEGACY SECTORS PER SLICE - USED IN CAPACITY CALC
+	LD	HL,SPS_HD512	; LEGACY SECTORS PER SLICE
+	LD	(SPS),HL	; SAVE IT
+;
 	; FLUSH DSKBUF TO MAKE SURE IT IS SAFE TO USE IT.
 	CALL	BLKFLSH		; MAKE SURE DISK BUFFER IS NOT DIRTY
 	XOR	A		; CLEAR ACCUM
@@ -1441,9 +1433,6 @@ DSK_MBR1:
 	LD	C,A		; PUT IN C
 	LD	DE,0		; LBA SECTOR ZERO
 	LD	HL,0		; ...
-#IFDEF PLTWBW
-	SET	7,D		; MAKE SURE LBA ACCESS BIT SET
-#ENDIF
 	CALL	DSK_IO2		; DO IT
 	RET	NZ		; ABORT ON ERROR
 ;
@@ -1487,6 +1476,8 @@ DSK_MBR3:
 	; CHECK THAT REQUESTED SLICE IS "INSIDE" PARTITION
 	; SLICE SIZE IS EXACTLY 16,384 SECTORS (8MB), SO WE CAN JUST
 	; RIGHT SHIFT PARTITION SECTOR COUNT BY 14 BITS
+	; IMPLEMENTED BY : LEFT SHIFT BY 2, AND TAKE HIGH ORDER WORD
+	; SAME AS DISCARDING THE LOWER 14 BITS, SINCE KEEP 2 BY SHIFT
 	LD	E,(HL)		; HL POINTS TO FIRST BYTE
 	INC	HL		; ... OF 32 BIT PARTITION
 	LD	D,(HL)		; ... SECTOR COUNT,
@@ -1510,7 +1501,7 @@ DSK_MBR3:
 ;
 DSK_MBR4:
 	; IF BOOT FROM PARTITION, USE NEW SECTORS PER SLICE VALUE
-	LD	HL,16384	; NEW SECTORS PER SLICE
+	LD	HL,SPS_HD1K	; NEW SECTORS PER SLICE
 	LD	(SPS),HL	; SAVE IT
 
 	; UPDATE MEDIA ID
@@ -1519,18 +1510,19 @@ DSK_MBR4:
 ;
 DSK_MBR5:
 	; ADJUST LBA OFFSET BASED ON TARGET SLICE
+	; ALSO JP HERE IF NO PARTITION TABLE, OR NO CPM PARTION
 	LD	A,(SLICE)	; GET SLICE, A IS LOOP CNT
 	LD	HL,(SEKLBA)	; SET DE:HL
 	LD	DE,(SEKLBA+2)	; ... TO STARTING LBA
 	LD	BC,(SPS)	; SECTORS PER SLICE
 	RES	7,D		; CLEAR LBA MODE BIT
-DSK_MBR6:                       
+DSK_MBR6:
 	OR	A		; SET FLAGS TO CHECK LOOP CNTR
 	JR	Z,DSK_MBR8	; DONE IF COUNTER EXHAUSTED
 	ADD	HL,BC		; ADD ONE SLICE TO LOW WORD
 	JR	NC,DSK_MBR7	; CHECK FOR CARRY
 	INC	DE		; IF SO, BUMP HIGH WORD
-DSK_MBR7:                       
+DSK_MBR7:
 	DEC	A		; DEC LOOP DOWNCOUNTER
 	JR	DSK_MBR6	; AND LOOP
 DSK_MBR8:
@@ -1552,21 +1544,11 @@ DSK_MBR9:
 	LD	(CAP_REQ),HL	; LSW
 	LD	(CAP_REQ+2),DE	; MSW
 ;
-#IFDEF PLTWBW
-	; GET DSK_CAP (DE:HL)
-	LD	B,BF_DIOCAP	; HBIOS DISK CAPACITY FUNC
-	LD	A,(SEKUNIT)	; DISK UNIT NUMBER
-	LD	C,A		; ... INTO C
-	RST	08		; HBIOS CALL (DE:HL = CAPACITY)
-#ENDIF
-;
-#IFDEF PLTUNA
 	; GET DSK_CAP (DE:HL)
 	LD	C,$45		; UBIOS DISK INFO FUNC
 	LD	A,(SEKUNIT)	; DISK UNIT NUMBER
 	LD	B,A		; ... INTO B
 	RST	08		; CALL UNA (DE:HL = CAPACITY)
-#ENDIF
 ;
 	; SAVE DSK_CAP (DE:HL)
 	PUSH	DE		; SAVE DSK_CAP (MSW)
@@ -1591,9 +1573,12 @@ DSK_MBR9:
 	OR	$FF		; SIGNAL ERROR
 	RET			; DONE
 ;
+#ENDIF
+;
 DSK_MBR10:
 	; FINALIZE SLICE LBA
 	SET	7,D		; SET LBA ACCESS FLAG
+DSK_MBR11:
 	; RESAVE IT
 	LD	(SEKLBA),HL	; LOWORD
 	LD	(SEKLBA+2),DE	; HIWORD
@@ -1601,7 +1586,7 @@ DSK_MBR10:
 	XOR	A		; SUCCESS
 	RET			; DONE
 ;
-;
+; CHECK DISK STATUS (PART OF BIOS COLD WARM BOOT)
 ;
 DSK_STATUS:
 #IFDEF PLTUNA
@@ -1619,21 +1604,21 @@ DSK_STATUS:
 	RET
 #ENDIF
 ;
-;
+; READ PHYSICAL SECTOR INTO BUFFER
 ;
 DSK_READ:
 	; SET B = FUNCTION: READ
 	LD	B,BF_DIOREAD
 	JR	DSK_IO
 ;
-;
+; WRITE PHYSICAL SECTOR FROM BUFFER
 ;
 DSK_WRITE:
 	; SET B = FUNCTION: WRITE
 	LD	B,BF_DIOWRITE
 	JR	DSK_IO
 ;
-;
+; READ/WRITE PHYSICAL SECTOR
 ;
 DSK_IO:
 	LD	A,(HSTUNIT)		; GET UNIT
@@ -1671,8 +1656,8 @@ LBA_IO:
 	LD	L,A
 	; ADD IN LBA OFFSET FOR PARTITION AND/OR SLICE
 	LD	BC,(HSTLBA)		; LBA OFFSET LOWORD
-	ADD	HL,BC	
-	EX	DE,HL	
+	ADD	HL,BC
+	EX	DE,HL
 	LD	BC,(HSTLBA+2)		; LBA OFFSET HIWORD
 	ADC	HL,BC
 	EX	DE,HL
@@ -1816,8 +1801,10 @@ DEFDRIVE	.DB	0		; DEFAULT DRIVE
 CCPBUF		.DW	0		; ADDRESS OF CCP BUF IN BIOS BANK
 MEDID		.DB	0		; TEMP STORAGE FOR MEDIA ID
 SLICE		.DB	0		; CURRENT SLICE
+#IFDEF PLTUNA
 SPS		.DW	0		; SECTORS PER SLICE
 CAP_REQ		.DW	0,0		; LBA CAP REQUIRED FOR SLICE
+#ENDIF
 STKSAV		.DW	0		; TEMP SAVED STACK POINTER
 ;
 #IFDEF PLTWBW
@@ -2596,7 +2583,7 @@ MD_INIT:
 	LD	A,(HCB + HCB_RAMD_BNKS)	; RAM DISK SIZE IN BANKS
 	LD	IX,DPB_RAM		; ADDRESS OF DPB
 	CALL	MD_INIT1		; FIX IT UP
-;	
+;
 	JR	MD_INIT4		; DONE
 ;
 MD_INIT1:
diff --git a/Source/HBIOS/hbios.asm b/Source/HBIOS/hbios.asm
index d5cc3540..114f7001 100644
--- a/Source/HBIOS/hbios.asm
+++ b/Source/HBIOS/hbios.asm
@@ -5263,11 +5263,11 @@ SYS_GETDIOMED:
 	; SAVE CALL ARGUMENTS
 	LD	(DIOMED_SLICE),DE	; STORES DE -> SLICE/UNIT PARAMETERS
 
-	; READ DEVICE INFORMATION USING DIODEVICE FUNTON
+	; READ DEVICE INFORMATION USING DIODEVICE FUNCTION
 	LD	A,(DIOMED_UNIT)
 	LD	C,A			; UNIT ID PARAMETER INTO C
 	LD	B,BF_DIODEVICE		; DRIVER FUNCTION = DISK MEDIA
-	CALL	DIO_DISPATCH		; CALL DIO TO GET MEDIAID (RESULT IN E)
+	CALL	DIO_DISPATCH		; CALL DIO TO GET DEVICE ATTRIBUTES
 	RET	NZ			; ABORT ON ERROR
 ;
 	; DEVICE ATTRIBUTES IN C
@@ -5298,7 +5298,7 @@ SYS_GETDIOMED1A:
 	; RETURN MEDIA ID (NOT HD) WITH SUCCESS
 	LD	DE,0			; LBA VALUE WILL BE ZERO
 	LD	HL,0
-	JP	SYS_GETDIOMED6A		; RETURN SUCESS
+	JP	SYS_GETDIOMED6A		; RETURN SUCCESS
 ;
 SYS_GETDIOMED1B:
 	; FOUND HD, NEED TO PROCESS MBR / PART TABLE
diff --git a/Source/UBIOS/ubios.inc b/Source/UBIOS/ubios.inc
index 58684c02..b906058d 100644
--- a/Source/UBIOS/ubios.inc
+++ b/Source/UBIOS/ubios.inc
@@ -25,3 +25,8 @@ MID_FD360	.EQU	7
 MID_FD120	.EQU	8
 MID_FD111	.EQU	9
 MID_HDNEW	.EQU	10
+;
+; SECTORS PER SLICE
+;
+SPS_HD512	.EQU	$4100
+SPS_HD1K	.EQU	$4000
diff --git a/Source/ver.inc b/Source/ver.inc
index 8510edde..05139b74 100644
--- a/Source/ver.inc
+++ b/Source/ver.inc
@@ -2,7 +2,7 @@
 #DEFINE	RMN	5
 #DEFINE	RUP	0
 #DEFINE	RTP	0
-#DEFINE BIOSVER	"3.5.0-dev.89"
+#DEFINE BIOSVER	"3.5.0-dev.90"
 #define rmj	RMJ
 #define rmn	RMN
 #define rup	RUP
diff --git a/Source/ver.lib b/Source/ver.lib
index b9fd306b..1ce0bc10 100644
--- a/Source/ver.lib
+++ b/Source/ver.lib
@@ -3,5 +3,5 @@ rmn	equ	5
 rup	equ	0
 rtp	equ	0
 biosver	macro
-	db	"3.5.0-dev.89"
+	db	"3.5.0-dev.90"
 	endm