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DISK DRIVE OPERATION
SpinPoint V40 Product Manual
35
The SID2001 Disk Controller manages the flow of data between the Data Synchronizer on the Read/Write IC
and its AT Interface Controller. It also controls data access for the external RAM buffer. The ENDEC of
88C5200 decodes the 32/34 with post-processor format to produce a serial bit stream. This NRZ (Non
Return to Zero) serial data is converted to 8-bit bytes.
The Sequencer module identifies the data as belonging to the target sector. After a full sector is read, the
SID2001 checks to see if the firmware needs to apply an ECC algorithm to the data.
The Buffer Control section of the SID2001 stores the data in the cache and transmits the data to the AT bus.
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 SID2001 Interface Controller. The Buffer Controller section of the
SID2001 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 32/34 GCR format and pre-compensates for non-linear
transition shift. The amount of write current is set by the SID2001 DSP and Interface/Disk Controller
through the serial interface to the preamp.
The SID2001 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
• Ten way burst ECC Correction
• SMART (Self-monitoring and reporting technology)
• Dynamic Anti-stiction Algorithm
5.5.1 Read Caching
SpinPoint V40 hard disk drives use a 512KB 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 disk requests are sequential. It takes microseconds rather than milliseconds to retrieve this cached data.