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M2266S1 H
Technical Handbook
Continuous Block Processing
The addressing method of data blocks is logical block address. The initiator
can access data by specifying the block number in a logically continuous data
space without regard to the physical structure of the track or of cylinder
boundaries.
The continuous processing of up to 64K blocks in a command can be
achieved, aid the IDD can perform continuous read/write operations when
processing data blocks across track or cylinder boundaries.
256KB Data Buffer
Data is transferred between the SCSI bus and the disk media through the
embedded 256KB data buffer in the IDD.
Since the initiator can control the disconnect/ reconnect timing on the SCSI
bus by specifying the condition of stored data to the data buffer or empty
condition of the data buffer, the initiator can perform the effective
input/output operations by utilizing the high data-transfer capability of the
SCSI bus, regardless of the actual data transfer rate of the disk drive.
Read-Ahead Cache Feature
After executing the READ command, the IDD reads automatically and stores
(prefetches) the subsequent data blocks into the data buffer (Read-Ahead
caching.) This function may be programmed to prefetch data in amounts
from one sector's worth to 256 Kbytes of data.
The high-speed sequential data access can be achieved by transferring the
data from the data buffer without reaccessing the disk in case the subsequent
command requests the prefetched data blocks.
Command Stack Feature
The command stack feature of the IDD corresponds to up to seven initiators.
Therefore, the IDD can accept and stack the input/output command issued
by another initiator even if the IDD is executing another command. The
stacked command is retrieved and executed in stacked order after the
present command has completed execution.
Reserve and Release Functions
The IDD can be accessed exclusively in the multi-host or multi-initiator
environment by using the reserve and release functions.
Fujitsu America, Inc.
FS810125-01 . . . A
1-3
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