Owner`s manual
Page 6-11Setting up Your System
dev
is the name of the disk device you want to set up write buffering for.
buffer-size
is
the size of the write buffer;
flush-time
is the maximum length of time data can be in the
write buffer before being written to disk.
For example:
SYSTEM DVR:SUB/N 200K 30
This sets up write buffering for all drives using the SUB driver. The write buffer can hold
up to 200K of data, and, even if the disk is busy, any pending data will be written to disk
after 30 seconds.
Even though you don’t need to load the DSK driver into system memory, you can turn
on write buffering for DSK devices by adding a SYSTEM statement for the DSK driver
using the format above.
If your computer supports write buffering, you can find more information in your
Owner’s
Manual
or other system documentation.
6.9.2Defining Floppy Disk Drivers to Use Buffered I/O
The SYSTEM command can define floppy disk drivers to use buffered input/ouput.
Doing so sets up a buffer pool for the device associated with the driver, and the number
of physical disk accesses is greatly reduced, thereby increasing floppy transfer speed.
In order to get a performance improvement, the driver must be loaded into system
memory at boot time by placing a command with this format in the initialization file:
SYSTEM DVR:[driver-name].DVR/N {number-of-file-updates}
where
driver-name
is the three-letter device name given to the driver when it was
configured, and
number-of-file-updates
is the number of file (and hence bitmap)
updates that will take place each time before buffered bitmap and directory information
is flushed to the floppy when "buffered writes" are active (see the MOUNT command in
your
System Commands Reference Manual
). Leaving this option out causes the driver
to default to "every" file update. Leaving the "/N" option off completely, or not loading
the driver into system memory, causes the driver to perform traditional unbuffered
input/output, providing no performance improvement. Here is an example:
SYSTEM DVR:MIN.DVR/N 20
This method of buffered floppy disk access does not work with drivers using the AM-219
controller.
System Operator’s Guide to the System Initialization Command File, Rev. 03