IBM L40 SX, Quick Reference

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Appendix A. Additional Information 86
The IBM Disk Cache
Technical Information
IBMCACHE.SYS is a device driver that allows a portion of the
computer memory to be used as a fixed disk cache (see the DOS
manual for information about device drivers and the Buffers
command). It can speed up application programs by keeping in the
cache fixed disk data that is accessed repeatedly. When an
application program requests fixed disk data that is already in the
cache, the data is sent directly to the application program. This is
quicker than if the data had to be read from the fixed disk again. Only
one IBMCACHE.SYS device driver can be installed. It uses about
8KB of memory plus the size of the cache. All fixed disks attached to
the computer are supported.
The installation program IBMCACHE.COM copies IBMCACHE.SYS
from the backup copy of the Reference Diskette to the root directory
of fixed disk drive C, and creates or modifies the fixed disk CONFIG.
SYS tile to contain a statement with this format:
device = \ibmcache.sys [sssss] [/E] [/Pn]
[sssss] is the cache size in K Bytes, and is specified as a decimal
value. The valid range is 16 to 512 if low memory is used, 16 to
15360 if extended memory is used. The default cache size is 64KB
for low memory, 128KB for extended memory.
[/E] tells IBMCACHE.SYS to use extended memory. The default
condition is for IBMCACHE.SYS to use low memory.
Note: High-speed communications may overrun and create data
Terrors if the cache is in extended memory. Also, IBMCACHE.SYS is
compatible with VDISKSYS, but may possibly conflict with other
extended memory applications.
[/Pn] is the cache page size in sectors. Valid values for n are 2, 4,
and 8. The default page size is 4. Some application programs may
perform better with different page size values.