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## RQDX and MFM disks

    Formatting non-DEC disks in the MicroVAX/VAXstation-2000
    --------------------------------------------------------

      Some of this information I figured out by reading STARLET and the
    example device drivers in the VMS _Device Support_ manuals.  Much of
    it was contributed to me by Terry Kennedy, Lennart Boerjeson, and
    others.

      The standard DEC drives that are supported in the VS2000 and their
    industry equivalents are:

    	RD54 - Maxtor XT-2190
    	RD53 - Micropolis 1325 or 1335
    	RD32 - Seagate ST-251-1

    If you have any of these standard drives you can simply plug it into
    your 2000 and the ROM formatter will automatically recognize the drive
    types.  I've never seen this fail, even if the drive has never seen a
    DEC machine before, or even if the drive was previously formatted in
    a PC.

      If the VS2000 ROM formatter program does not recognize one of these
    drive types, then it will enter a dialog asking you to enter the drive
    parameters described below.  Again, I've never seen this fail, even
    with very old ROM firmware versions (v1.2 is the oldest I've seen).
    If you get a "??" response rather than the dialog, you almost certainly
    have a hardware problem with your drive.

      In theory you can use ANY MFM drive in the VS2000 by calculating
    the appropriate parameters.  I've done this with several non-DEC
    drives with good success now, and following is a description of what
    I've learned about the parameters.  If you can contribute to any
    of the "I don't know" parts, I'd like to hear about it!

    ------------------------------------------------------------------------

    XBNSIZ - I've no idea what an XBN is!  All DEC's disks seem to use 54,
    	 regardless of the disk capacity.

    DBNSIZ - number of diagnostic blocks.  DEC seems to select this so that the
    	 DBNs and XBNs total up to 1 cylinder.  Therefore:

    		DBNSIZ = (SURPUN*17) - XBNSIZ

    LBNSIZ - total number of user data blocks, not counting DBNs and XBNs.
    	 I believe that

    		LBNSIZ = CYLPUN * SURPUN * 17

    	 the numbers I have for DEC disks are close to this, but not
    	 exact.  There must be some ambiguity about what gets counted.

    RBNSIZ - replacement block count (for bad block revectoring).  About 0.1%
    	 to 1% of the disk capacity is reasonable, depending on the media
    	 quality.  DEC seems to always use 0.2%.  This is frequently
    	 rounded to an exact number of cylinders, but I'm not sure that's
    	 necessary.  WARNING - if you allocate fewer RBNs than your disk
    	 has bad sectors, the VS2000 formatter seems to hang in the media
    	 analysis phase!

    SURPUN - surfaces (aka heads) per drive.  Note that the RQDX? will ALWAYS
    	 assume 17 sectors per track, 512 bytes per sector!  The RQDX
    	 controllers can handle a maximum of 16 heads.

    CYLPUN - cylinders per drive.  Total number of cylinders on the drive.
             I believe, but I'm not sure, that this does NOT include the
    	 cylinders used for DBNs, RBNs and XBNs.  Note that the RQDX
    	 family controllers can handle a maximum of 2048 cylinders
    	 (but I don't think there were ever any MFM drives made with
    	 even close to that number!).

    WRTPRC - cylinder to start write precompensation.  If your drive doesn't
    	 need write precomp (almost none do), then enter a value larger
    	 than the last cylinder.

    RCTSIZ - size of the Replacement (i.e. Bad Block Replacement) and Caching
    	 Table.  From the structure of the RCT, I believe this can be
    	 calculated as

    		RCTSIZ = (44 + 4*RBNSIZ) / 512

    	  but unfortunately this doesn't give the values DEC uses for
    	  their drives!  You could also just use the RCTSIZ from the
    	  closest sized DEC disk.

    RCTNBR - number of copies of the RCT.  I'm not sure of the significance
    	 of this, but DEC disks always use 8.

    SECITL - sector to sector interleave.  The RQDX is fast enough to support
    	 1 (i.e. no interleaving).  Anything larger will reduce thruput.
    	 SECITL is a function of the disk rotational speed, and is the same
    	 for all MFM drives regardless of capacity.

    STSSKW - delay for switching heads.  I don't know how to calculate this or
    	 even what units it's expressed in!  All drives seem to use 2.

    CTCSKW - delay for track-to-track seek.  I don't know how to calculate this
    	 or even what units it's expressed in!  All DEC drives use 8.

    MEDIAI - media identification code.  This is a 32 bit value which the ROM
    	 wants you to enter in DECIMAL, not hex!  Standard values are:

    		RD32 - 627327008
    		RD53 - 627327029
    		RD54 - 627327030

    	 The last section explains how the media id is calculated if you
    	 are interested.  If you use a non-DEC media id, be aware of two
    	 things: (1) the ROM disk diagnostic won't work, and (2) the VMS
    	 MSCP cluster server won't serve the disk.

    ------------------------------------------------------------------------

    Here are the parameter values for some DEC disks, and those that I've
    successfully used for a Seagate ST-4097 (an 80Mb drive).

    		  RD54		  RD53		ST4097
    		------		------		------
    XBNSIZ		    54		    54		    54
    DBNSIZ		   201		    82		    99
    LBNSIZ		311256		138672		156060
    RBNSIZ		   609		   280		   306
    SURPUN		    15		     8		     9
    CYLPUN		  1221		  1020		  1021
    WRTPRC		  1221		  1020		  1024
    RCTSIZ		     7		     5	             5
    RCTNBR		     8		     8		     8
    SECITL		     1		     1		     1
    STSSKW		     2		     2		     2
    CTCSKW		     8		     8		     8
    MEDAI	     627327030	     627327029	     627327029

    ------------------------------------------------------------------------

    Media Identification Code

      The media id is a longword (32 bit) value composed of five 5-bit
    alphabetic characters and one 7-bit binary value.  The five characters
    start from bit 31 (the MSB) of the longword and are encoded as 0=null,
    1='A', 2='B', etc.  Only letters (and a null) can be represented.

      The first two characters represent the media type (e.g. "DU") and
    the next three are the name of the media currently mounted (e.g.
    "RD" or more accurately, "RD").

      The 7-bit binary value is the numeric part of the media name
    (e.g. 32, 53, 54, etc).

      For example, for an RD54 we have

    	D	U	R	D		54
    	00100	10101	10010	00100	00000	0110110

    Write this down as a 32 bit hex value and we have 0x25644036 or
    627327030 (decimal).

    ------------------------------------------------------------------------

    If he couldn't figure out the answers to the VS2000 formatter, he's
    not going to have any easier time with ZRQC!  Remember, he's formatting
    disks that have never been formatted on a VS2000 or RQDX3 before, so
    he needs all the numbers necessary to MSCP-qualify the disk.

    Here's the RD52 numbers, straight from the RQDX3 DEC-internal docs:

    					Quantum		Atasi
    					-------		-----
    Sector Interleave			1:1		1:1
    Bytes/Sector				512		512
    Sectors/LBN				1		1
    LBNs/Track				17		17
    Tracks/Group				8		7
    Groups/Cylinder				1		1
    Cylinders/Unit				512		645
    Total LBN's/Unit			69632		76755
    RBNs/Unit				168		168
    RCT Size (Blocks)			4		4
    RCT Copies				8		8
    DBNs/Unit				8		8
    XBNs/Unit				54		54
    User LBNs/Unit				60480		60480
    User Capacity (Bytes)			30965760	30965760
    Step Pulsewidth (usec)			11.2		11.2
    Step Rate (usec)			17.6		17.6
    Write Precomp (nsec)			10		10
    Precomp Cylinders			256-611		320-644

    And, for completeness, the RD51 and RD53 numbers (though I suspect
    the DEC tables have typos for at least some of the RD51 quantities):

    					RD51		RD53
    					----		----
    Sector Interleave			1:1		1:1
    Bytes/Sector				512		512
    Sectors/LBN				1		1
    LBNs/Track				18		17
    Tracks/Group				1		8
    Groups/Cylinder				4		1
    Cylinders/Unit				306		1024
    Total LBN's/Unit			22032		139264
    RBNs/Unit				144		280
    RCT Size (Blocks)			36		5
    RCT Copies				4		8
    DBNs/Unit				87		82
    XBNs/Unit				57		54
    User LBNs/Unit				21600		138672
    User Capacity (Bytes)			11059200	71000064
    Step Pulsewidth (usec)			11.2		11.2
    Step Rate (usec)			17.6		17.6
    Write Precomp (nsec)			10		(none)
    Precomp Cylinders			110-305		(none)

    Tim Shoppa

    ------------------------------------------------------------------------

    What jumper seting are required to make a Micropolis 1325 look like a RD53 ?

    Unscrew the two screws holding the circuit board to the bottom of the drive
    and carefully lift it up.  Along one edge of the circuit board you will find
    a place where it would appear that a resistor should be -- this place is
    marked R7.  Solder a jumper into that spot to make this drive into an RD53.
    Set the drive select jumper to DS2 and you should be in business.

    Bob Hoffman