Hardware Reference
In-Depth Information
As you can see from the information in
Table 11.8
,
the spiral track is divided into sectors
that are stored at the rate of 676 sectors per second. Each sector contains 2,048 bytes of
data.
When being written, the sectors are first formatted into data frames of 2,064 bytes: 2,048
are data, 4 bytes contain ID information, 2 bytes contain ID error-detection (IED) codes,
6 bytes contain copyright information, and 4 bytes contain EDC for the frame.
ThedataframesthenhaveECCinformationaddedtoconvertthemintoECCframes.Each
ECC frame contains the 2,064-byte data frame plus 182 parity outer (PO) bytes and 120
parity inner (PI) bytes, for a total of 2,366 bytes for each ECC frame.
Finally, the ECC frames are converted into physical sectors on the disc. This is done
by taking 91 bytes at a time from the ECC frame and converting them into recorded
bits via 8-to-16 modulation. This is where each byte (8 bits) is converted into a special
16-bit value, which is selected from a table. These values are designed using an RLL 2,10
scheme, which is designed so that the encoded information never has a run of fewer than
two or more than ten 0 bits in a row. After each group of 91 bytes is converted via the
8-to-16 modulation, 32 bits (4 bytes) of synchronization information are added. After the
entire ECC frame is converted into a physical sector, 4,836 total bytes are stored.
