Hardware / Central Point Software / Deluxe Option Board


Exploring the low-level structure of a IBM floppy disk

Update: 27.06.2020

First you have to wait really long until you can buy an Option Board for a normal price on ebay and suddenly you get two pieces within three weeks. The last one cost me $13. I do not have the words!


The Option Board is not a floppy disk controller. You must always put the Option Board between the floppy disk drive and the floppy disk controller.

The Deluxe Option Board can be thought of as a disk accessory. It adds new capabilities to your existing disk drive by acting as an auxiliary floppy controller.

The standard floppy disk controller is actually a simple computer on its own. When the PC wants some information from the disk, it asks the floppy disk controller’s “computer” to get it. The information that the PC receives is only the information contained in the data fields. You have no access to the information between the data fields. Using the Deluxe Option Board, this limitation is overcome. It can access all of the information contained on the disk bit-by-bit.

It simply transfers every bit of data from your original diskette onto the backup.

The Deluxe Option Board technology is the same that is used by many software duplication firms who add copy protection to disks. Therefore, it is possible to use the Deluxe Option Board to make archival copies of virtually all copy-protected PC software. It is required because most copy schemes rely on quirks of the standard floppy disk controller. Since the Deluxe Option Board is not limited by the floppy controller’s capabilities, it is possible to make backups of some of the newer protection schemes which software-only programs such as Copy II PC cannot.

Since the Deluxe Option Board is able to copy disks bit-by-bit, it does not require the disk to be of a particular format to copy. Therefore, you can make copies of Atari, Commodore and other non-IBM format disks that are not copy-protected. The software verifies the disks, but does not qualify them.
Deluxe Option Board manual (1988, 1989)

Known models

Deluxe Option Board

Central Point Software / Deluxe Option Board
Fig. 1: Central Point Software / Deluxe Option Board / Transcopy3 IC



TC - Transition Copier

It is very important to differentiate between 1.2M/1.44M DISKS (FLOPPIES) and 1.2M/1.44M DRIVES!

The Deluxe Option Board will work on either a 1 or 2 floppy drive system. It can use 360K, 1.2M, 1.44M, or 720K drives with the following limitations/conditions:

- Both the source and target drive must be PHYSICALLY configured as the A or B drive within the system (not logically configured with DOS).
- Both drives must be internal (not connected to the external drive port).

- Can read from a 1.2M drive and write to a 360K or 720K drive.
- Can read from a 1.2M drive and write to a 1.2M drive.
-> Cannot read from or write to 1.2M disks!

- Can read from a 1.44M drive and write to a 360K or 720K drive.
- Can read from a 1.44M drive and write to a 1.44M drive.
-> Cannot write to 1.44M disks!
Option Board Manual
Transition Copier (TC)
Fig. 2: Transition Copier (TC), V5.4

Note: Only versions 5.x can be used for the Deluxe Option Board with TRANSCOPY3 chip. With my DOB's the versions 5.18 or 5.20 were included. The 4 series version probably need the normal OB without TRANSCOPY chip.

MCP - Macintosh Control Program

The Deluxe Option Board allows you to transfer data files between an Apple Macintosh and a PC or PS/2. File transfers, however, do not provide the ability to run Macintosh programs on a PC system.

In order to use this feature, all you need is an internal 3.5 inch disk drive in your PC or PS/2. The Deluxe Option Board will transform your IBM 720K or 1.44M 3.5” drive into a dual-purpose IBM/Macintosh drive.

MCP enables you to transfer files between the Macintosh and IBM versions of popular programs such as Microsoft Word, PageMaker, dBase Macintosh, Microsoft Excel, and Lotus l-2-3. For example, many word processing programs support a standard file exchange protocol called DCA. By saving a document in DCA format, you can load it into a different program with minimal disruption of formatting information.
Deluxe Option Board manual (1989)

I have tried MCP a few times. The formatting (MFORMAT) with 400K (SS, MFS) and 800K (DS, HFS) usually works fine. Also copying (MCOPY) and displaying (MTYPE) of text files usually works.

I can't say more about this program, because I don't have an old Macintosh system (e.g.: Macintosh 128K). But in principle it seems to work.

TE - Transition Editor

Externally this editor looks like a normal HEX editor. Far from it. With this editor you can read/write a whole TRACK and view/edit the areas between two data sectors, the GAP bytes and the SYNC bytes. Other HEX editors cannot do that! This program is also called track editor (TE).

Transition Editor (TE)
Fig. 3: Transition/Track Editor (TE)

In track 0 you can see that there are 204 "other" bytes before the actual data sector starts at 0x00CC -> EB FE 90. This disk was IBM PC-DOS formatted with Uniform-PC (180K, SS, DD). You can verify this, when you look at the BPB (magenta dots, starting at 0x00D7)

The 0x4E are GAPs interrupted with the SYNC bytes (0x00) and the address marks (IDM: 0xC2, 0xC2, 0xC2, 0xFC // IDAM: 0xA1, 0xA1, 0xA1, 0xFE // DAM: 0xA1, 0xA1, 0xA1, 0xFB).

A track contains 9 sectors of 512 bytes of data. This are 4,608 bytes. A complete track consists of about 6,230 bytes maximum. In other words, a maximum of 2/3 of the bytes are used for data. The rest is required to synchronize the sectors of the floppy disk.

disk structure
Fig. 4: Disk structure / MFM encoding

s = start of the track / the sector 1 starts at 0x0090 (IDAM)

The ID of each sector always follows the byte sequence A1A1A1FE (IDAM). The following three bytes describe the sector identification (ID) after the key CHS: Cylinder, Head, Sector. The fourth byte is the so-called size ID byte. 02 means 512 byte; see orange dots.

In the first sector of the second track I wrote manually with the Norton HEX Editor NU the characters ABCDEFGH. The TE Editor shows this correctly.

Forensic Computing: A Practitioner’s Guide
Fig: 5: Forensic Computing: A Practitioner’s Guide (Anthony Sammes, Brian Jenkinson)

IAM = Index Address Mark, IDAM = (sector) ID Address Mark, DAM = Data Address Mark

One complete sector consists of 654 bytes (512 + 142).

Track length: 146 + 9 x 654 + 200 = 6.232 Byte (see figure above, TE hardcopy: 6.228 or 6.230 bytes). These numbers are not one hundred percent correct because there are always small deviations, especially in the gap bytes. I once counted the "GAP 4B" bytes at the end of the first track. It is actually 277 and not 200. But I have also read tracks that had 0x185A bytes (6,234).

A little disk arithmetic. 6,232 times 40 tracks gives 249,280 unformatted bytes, or 243K. 512 times 9 times 40 makes 184,320 bytes, or 180K, that is ok. 6,232 bytes per track are actually a bit too little. It should be 250k times 1,024 divided by 40 equals 6,400 bytes per track.

However, the basic systematic and the above Table 5.2 are correct.

MFM track formatting comparison
Fig. 6: Shugart SA850/851 Bi Service Manual - 1980
IBM standard MFM track format
Fig. 7: IBM standard MFM track format
Note: The assignment of the colours to the markings in figures 4 and 7 do not correspond 100%. This is due to the fact that I made figure 7 later and I did not work exactly with figure 4.

In each sector there are always two characteristic address marks (AM). They always start with 3 times A1h followed by a FEh or FBh. If the byte sequence is A1A1A1 FE, then it is the ID address mark (IDAM) and the ID with the CHSB information (Cylinder, Head, Sector, Byte) follows. If the byte sequence is A1A1A1 FB, then it is the data address mark (DAM) and the actual data area of 512 bytes follows immediately.

To be continued: Here you can see how the first track of a disk with the KryoFlux looks like (RAW data stream): „Exploring an IBM standard MFM track of a floppy disk“


For those who want to go even deeper into the subject, I recommend the following website. Please do not be confused by the keyword ATARI. Many aspects also apply to the IBM PC.