Document 1205
Slow Disk Transfers

Description:

Some customers may experience very slow data transfer rates when
their applications are doing direct disk input. The slow
transfer rate is a result of how DR DOS handles device drivers
or applications which use upper memory blocks while writing data
to the disk drive

Under DR DOS, disk access going through UMBs is transferred to
conventional memory before it is written. It is then written one
sector at a time. This reduces 1:1 interleave down to 17:1 which
results in disk writes being 3 to 8 times slower than disk
writes going directly through conventional memory. It is only a
problem with writes to the disk, not reads.

What would cause this slow transfer rate under DR DOS?

1) A disk I/O driver loaded into upper memory, such as the
Stacker disk compressor or Disk Manager. The workaround is to
load the driver in conventional memory.

Note: The DR DOS SuperStor driver averts this problem by leaving
the DMA TRANSFER part of its code in conventional memory.

2) An application that makes disk transfers through UMBs, such
as Lotus 3, Paradox 3, Autocad 386, Autocad 11.

Digital Research designed DR DOS to make disk writes through
conventional memory in order to protect customers with Bus
Master controllers (newer PS/2 models) or some older hardware.
Without this protection, data on their drives could be severly
corrupted. Digital Research is currently investigating this
problem. Please keep in contact with technical support for more
information.

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Slow disk access on older systems

Some customers with old systems, BIOS etc. report slow disk
access time.  This is not at initial log to the drive, but
rather during file reads from within specific applications. 
This is not resolved by eliminating memory manager, or booting
without TSR's, etc.  SUPERPCK cannot be run due to memory
limitations. Customers have reported that the problem is
resolved by using DRIVER.SYS in CONFIG.SYS.  After DRIVER.SYS is
loaded, refer to the drive with the new drive spec assigned; for
example, A: drive might be accessed with D:.  You may use the
command ASSIGN A=D, for example, in order to continue to access
the drive as A: for consistency with existing applications.

Note that DRIVEPARM does achieve the same results, because the
BIOS is still used for drive access.

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There is an apparent delay when first accessing a floppy drive,
during which DR DOS actually reads data from the disk. This
initial read will make subsequent commands from a floppy run
faster since the directory and FAT tables have already been
accessed.