BeebMaster - BeebHelp - Formatting ST-506 Winchester Discs

Formatting ST-506
Winchester Discs

What follows is intended to help ST-506 Winchester Disc owners to format their hard drives correctly for use with the BBC micro.

I am assuming the Winchester Disc unit is set up and functioning correctly. For complete Winchester units such as those supplied by Acorn, Technomatic, Cumana, Watford Electronics etc, all you should need to do is to plug the 34-way ribbon cable into the 1MHz bus and power up the Winchester and then you will be ready to format.

If you are putting together your own Winchester system, very briefly you will need:

1. Host Adapter Board (Acorn/Akhter etc)
2. ST-506 Disc Controller Board (Adaptec ACB4000/4070 etc)
3. ST-506 Winchester Disc Drive
4. 34-way ribbon cable (BBC 1MHz bus to Host Adapter Board)
5. 50-way ribbon cable (Host Adapter Board to Disc Controller Board)
6. 34-way ribbon cable (Disc Controller Board to ST-506 Disc Drive)
7. 20-way ribbon cable (Disc Controller Board to ST-506 Disc Drive)
8. Power supplies to power the Host Adapter, Disc Controller and Winchester Disc Drive

Drive Parameters

Firstly you will need to know the drive parameters of your Winchester Disc. A search on the internet will usually turn up the information you need. Make a note of the following:

1. Number of heads
2. Number of cylinders
3. Landing Zone
4. Whether it supports MFM (1,3) or RLL (2,7) recording
5. Formatted capacity (as a rough guide only)

MFM and RLL Recording

ST-506 Winchester Discs support either the MFM or RLL recording method. All you need to know is that RLL is higher density than MFM. On the BBC, RLL encoding formats 46 or 47 sectors per track. With MFM encoding, you get 32 or 33 sectors per track.

The higher number quoted here is peculiar to the Adaptec ACB range of controllers, which are able to squeeze an additional sector per track when an interleave factor of 1 used. Other controllers, such as the Xebec or Western Digital ones, cannot manage this.

You will also need to know whether your Winchester Disc Controller board supports MFM or RLL. Even if you have an RLL Winchester Disc, if your Controller only supports MFM, you will only be able to format the disc to 32 or 33 sectors per track.

The Adaptec controllers are the most common. The ACB-4000 (used in the Acorn Winchester Disc) is an MFM board. The ACB-4070 (used in the Technomatic Winchester Disc) is an RLL board.

An RLL Winchester Disc controller will allow you to format an MFM Winchester Disc to 46 or 47 sectors per track but you may experience problems with reliability as the disc is not intended to be formatted to the higher density.

Many Winchester Disc drives are in fact identical apart from the recording method they support. For example, the Miniscribe MS8425 and MS8438 are exactly the same except that Miniscribe certified the MS8438 as an RLL disc and the less reliable ones went out as MFM discs badged MS8425. You could probably format the MS8425 as an RLL disc but it might not last long.


Superform is the standard Winchester Disc formatting utility, but it is intended for the Adaptec controllers. There are various versions floating about, so it's important to make sure you are using the right one for the type of Adaptec controller being used. The only real difference is its use of the number of sectors per track. Make sure line 1 of Superform is either of the following:

1 sector-bodge=33

1 sector-bodge=47

Choose the "C" option from the menu and enter the drive parameters you made a note of earlier. Superform will format the disc to the parameters you specify and then verify the disc. It will create a defect list of any bad sectors on the disc.

Superform will repeat the format until all the bad sectors are mapped out. However, in some circumstances you may find that a recurrent bad sector occurs on each format. Unless you intervene, Superform will continually reformat forever.

If you find that Superform is going for more than an hour without finishing, you will need to change line 3920 to accept a number of bad sectors. Remember that K% is the number of bad sectors on the disc multiplied by 8. So for one bad sector remaining on the disc, change line 3920 to:


For two bad sectors, K%=16, etc., taking into account the number of recurring bad sectors appearing on each reformat.

When Superform has finished, it will save two copies of itself in a directory called "Format" as well as a copy of the defect list which will be taken into account every time there is a reformat.

Remember that the version of Superform saved on the disc will include any changes you have made.

Checking the Format

*FREE will tell you the disc capacity. Add up the number of free sectors and the number of used sectors to get the total number of sectors.

Check that this corresponds with the number of sectors you would expect on the disc. For an MFM disc this is:

Heads x Cylinders x 33

For an RLL disc, this is:

Heads x Cylinders x 47

The formatted capacity of the disc is the number of sectors x 256 as ADFS only supports 256 bytes per sector.

In order to preserve important data on the disc, I think it is always best to make sure all the formatted space is actually available on the disc.

To do this, I recommend creating alternatively a large file and a directory in the root directory of the disc.

For example:

*CREATE BIGFILE1 1000000 (to create a 16MB file - use 800000 for 8MB, 400000 for 4MB, 200000 for 2MB and 100000 for 1MB)


If the big file has taken up more space than is physically present, creating the directory will cause a disc error.

Repeat the process until the disc is full (adjusting the size of the last BIGFILE to use up all the remaining space) and then *DUMP the last big file created on the disc to check that all the disc space is available. To save time, you can use an offset in the DUMP command to start the dump part way through the file.

If the file dumps successfully, then all the formatted space is available. If not, then a disc error will occur at the last available sector on the disc. Divide this sector number by the number of heads and the number of cylinders in the disc and you will end up the number of sectors per track you can fit onto the disc. You can then re-format using this number as the sector-bodge parameter at line 1 of Superform.