Samsung M8-DVR manual Firmware Features, Write Channel, Read Caching

5.4.2The 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 receive 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

5.5.1Read 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 disk requests are sequential. It takes microseconds rather than milliseconds to retrieve this cached data. Thus Read Caching can provide substantial time savings during at least half of all disk requests. For example, Read Caching

Spinpoint M8-DVR Disti Product Manual REV 2.0 32