Hardware Reference
In-Depth Information
Only the following subset of DOS commands is valid within the CON-
FIG.SYS file:
Command
Function
Determines the response to a
<
CTRL-BREAK
>
sequence. If
you set
BREAK ON
in CONFIG.SYS, DOS checks to see whether
you have requested a break whenever a DOS call is made. If you
set
BREAK OFF
, DOS checks for a break only when it is working
with the video display, keyboard, printer, or a serial port.
BREAK
Sets the number of file buffers which DOS uses. This command can
be used to significantly improve disk performance with early versions
of DOS and when a disk cache (accessed via IBMCACHE.SYS or
SMARTDRV.SYS) is not available. The use of buffers can greatly
reduce the number of disk accesses that DOS performs (DOS only
reads and writes full sectors). Data is held within a buffer until it is
full. Furthermore, by reusing the least-recently used buffers, DOS
retains information more likely to be needed next.
It is worth noting that each buffer occupies 512 bytes of RAM
(plus 16 additional bytes overhead). Hence, the number of buffers
may have to be traded-off against the amount of conventional
RAM available (particularly in the case of machines with less
than the standard 640 KB RAM).
In general,
BUFFERS=20
will provide adequate for most
applications.
BUFFERS=40
(or greater) may be necessary for database
or other applications which make intensive use of disk files.
DOS uses a default value for
BUFFERS
of between 2 and 15
(depending upon the disk and RAM configuration).
Later versions of DOS (e.g. MS-DOS 4.1) provide a much
improved
BUFFERS
command which includes support for
expanded memory and look-ahead buffers which can store
sectors ahead of those requested by a DOS read operation. The
number of look-ahead buffers must be specified (in the range
0-8) and each buffer requires 512 bytes of memory and
corresponds exactly to one disk sector. The use of expanded
memory can be enabled by means of a
/X
switch.
Example:
BUFFERS=100,8 /X
sets the number of buffers to 100 (requiring approximately
52 KB of expanded memory) and also enables 8 look-ahead
buffers (requiring a further 4 KB of expanded memory).
BUFFERS
Sets the country-dependent information.
COUNTRY
Sets the hardware device drivers to be used with DOS.
Examples:
DEVICE=C:
\
MOUSE
\
MOUSE.SYS
enables the mouse driver (MOUSE.SYS) which contained in a
sub-directory called
MOUSE
.
DEVICE
(
continued
)
