Sample Track Format - Quantum Q2080 Product Description

The Q2080 is a soft-sectored drive and as such can use whatever format the use desires. When chosing or design-
ing a format for the Q2080 the following drive specifications must be considered:
1. Head switching time
2. Write to read recovery time
3. Spindle speed tolerances
4. Head, media and read write
channel characteristics -
20 microseconds maximum
20 microseconds maximum
19.75-21.00 milliseconds (rotational time)
These items are selected and optimized for MFM coding
at a transfer rate of 4.34MBITS/sec.
The soft sector format shown in Figure 3-1 is a slightly modified version of the IBM System 34 double density
format commonly used on 8 inch floppy disk drives. Data are encoded using the modified frequency modulation
(MFM) code.
INDEX
---.n' - ---___________
-4I~,
....
------------------....JrL
DATA FIELD
256 X USER DATA
I.D.A.M.
NOTE 5
OATAA.M
u~~i~-------------~
FIGURE 3-1
SAMPLE TRACK FORMAT
..
GAP3
15
x
'4E
NOTE 5
Each track is divided into 32 sectors with each sector containing a data field of 256 bytes.
GAP4
352 X '4E'
The beginnings of the sector ID field and the data field are defined by a unique field called an address mark.
This two byte field always has hexadecimal Al as the first byte. This byte is followed by hexadecimal FE in ID ad-
dress marks or hexadecimal FB in data address marks. To insure the recorded pattern of the address marks is unique
from all other data patterns, the Al byte is recorded with a missing clock bit. This encoding violates one of the rules
of the MFM code, while maintaining normal bit intervals used in MFM.
Each ID and data field is followed by a data verification field. This may be either a cyclic redundancy check
(CRC) field of 16 bits (2 bytes) or an error correction code (BCC) field of 24 or 32 bits (3 or 4 bytes). Various gap and
sync fields separate the ID and data fields.
The sync fields provide the data separator with periods of specific length in which bits are recorded in a known
and constant position. This allows the data separator to lock onto the present data rate and separate known clock
and data bits from the bit stream. The sync field length is determined by data separator performance characteristics.
Each of the four gaps are inserted to mask and/or compensate for various drive characteristics. Gap 1 provides
a period that masks the head switching time when formatting a track. When formatting, the controller starts writing
at index and continues until the next index is received, at which time the controller switches heads to the next track.
This allows one complete track to be formatted on each revolution of the disk. Gap 1 should be at least 11 bytes long
to allow for a head switching time of 20 microseconds. Gap 1 is immediately followed by the sync field for the sector
ID field of the first sector.
Gap 2 follows the sector ID field and separates it from the data ID field. This gap provides a period that masks
the write update splice and provides a sync field for the data ID field. The splice occurs when data is written into the
data field, because the new data may not be written exactly in phase with the old data. The length of Gap 2 is deter-
mined by: write oscillator tolerance which generates the write splice, data separator lock up performance which re-
quires a specific sync period, and drive spindle speed tolerance which determines where physically the splice may occur.
3-3 REV A (01/84)