Seagate Spinpoint M8, Product Manual

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Spinpoint M8 Product Manual REV 2.6
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5.4.2 The Write Channel
The signal path for the Write Channel follows the reverse order of that for the Read Channel. The host transmits
data via the AT bus to the 88i9422 Interface Controller. The Buffer Controller section of the 88i9422 stores the
data in the cache. Because the data is transmitted to the drive at a rate that exceeds the rate at which the drive can
write data to the disk, data is stored temporarily in the cache. Thus, the host can present data to the drive at a rate
independent of the rate at which the drive can write data to the disk.
Upon correct identification of the target address, the data is shifted to the Sequencer, which generates and appends
an error correcting code. The Sequencer then converts the bytes of data to a serial bit stream. The AT controller
also generates a preamble field, inserts an address mark, and transmits the data to the ENDEC in the R/W IC where
the data is encoded into the LDPC format and pre-compensates for non-linear transition shift. The amount of
write current is set by the 88i9422 DSP and Interface/Disk Controller through the serial interface to the
preamplifier.
The 88i9422 switches the Preamplifier and Write Driver IC to write mode and selects a head. Once the
Preamplifier and Write Driver IC receives a write gate signal, it transmits current reversals to the head, which
writes magnetic transitions on the disk.
5.5 Firmware Features
This section describes the following firmware features:

Read Caching

Write Caching

Track Skewing

Defect Management

Automatic Defect Allocation

ECC Correction

SMART (Self-monitoring and reporting technology)

ATA security mode features

ATA host protected area

ATA streaming features

ATA power up in stand by feature set

ATA advanced power management (APM) feature set

ATA device configuration overlay (DCO) feature set
5.5.1 Read Caching
The Spinpoint M8 hard disk drive uses Read Cache to enhance drive performance and significantly improve
system throughput. Use the SET FEATURES command to enable or disable Read Caching. Read caching
anticipates host-system requests for data and stores that data for faster future access. When the host requests a
certain segment of data, the cache feature utilizes a prefetch strategy to get the data in advance and automatically
read and store the following data from the disk into fast RAM. If the host requests this data, the RAM is accessed
rather than the disk.
There is a high probability that subsequent data requested will be in the cache, because more than 50 percent of all