About CorelCDX
==============
To work with your CD-ROM drives, you require a CD-ROM
extensions program such as CorelCDX. CD-ROM extensions
programs interpret, for DOS, data read from High Sierra
and ISO-9660 formatted CD-ROM discs.
Unlike other CD-ROM extensions programs, CorelCDX also
caches CD-ROM data. Applications can access cached data
faster than re-reading the CD-ROM disc.
Table of Contents
-----------------
1. Loading and Unloading CorelCDX
2. CorelCDX Caching
3. Configuring CorelCDX
1. Loading and Unloading CorelCDX
-----------------------------------
CorelCDX is loaded from the AUTOEXEC.BAT file during
the system startup. The configuration of CorelCDX is
determined by its command line switches, which are
described in the topic, "Configuring CorelCDX".
If you need to free the memory or drive letters used
by CorelCDX, you can unload CorelCDX. The next time
you restart your system, CorelCDX is loaded again.
NOTE: CorelCDX may not unload if other TSR programs were
installed after CorelCDX was loaded. If problems occur,
unload the other TSR programs and then try to unload
CorelCDX again.
To unload CorelCDX, enter the following at the command
prompt:
CORELCDX /UNLOAD.
2. CorelCDX Caching
---------------------
CorelCDX includes several types of caches to provide
faster access to frequently used CD-ROM data. Path
table, directory, and data caches provide conventional
or expanded memory caching. As an extension to
CorelCDX, CDXCACHE provides an extended memory data
cache.
The path table cache stores information about the
name and location of each directory on the CD-ROM
disc. Each path table cache buffer accommodates
approximately 100 sub-directories.
The directory cache stores information such as the
name and location of the files in each directory on
the CD-ROM disc. Each directory cache buffer
accommodates approximately 40 to 50 files.
The data cache stores the contents of recently
accessed files from the CD-ROM disc and any data
that's expected to be required next. CorelCDX
uses a read-ahead plus least recently used (LRU)
algorithm for its data cache: frequently used data
remains in the cache and infrequently used data
is discarded from the cache. Data is read into
the cache in sector blocks.
CDXCACHE, if enabled, is loaded at the same time
as CorelCDX. This cache stores information recently
read from CD-ROM drives in extended memory.
CDXCACHE, like the data cache, uses an LRU algorithm
to determine the contents of the cache.
CDXCACHE can cache the first 16 CD-ROM drives
connected to your system. The cache page size
affects the maximum cacheable sector address.
CDXCACHE works best with database type applications,
which repeatedly read information from the same
areas of a CD-ROM disc.
CDXCACHE versus SMARTDrive:
Both CDXCACHE and Microsoft's SMARTDrive program
use extended memory caching. If you're using
SMARTDrive version 5.0, provided with MS-DOS 6.2,
you can use SMARTDrive rather than CDXCACHE.
However, CDXCACHE has smaller overhead and
operates faster than SMARTDrive.
SMARTDRV.EXE 5.0 is designed to work exclusively
with Microsoft's MSCDEX CD-ROM driver. However,
Corel's PATCH_SD.COM modifies SMARTDRV.EXE to
recognize CorelCDX as a valid CD-ROM driver.
PATCH_SD creates a copy of the existing
SMARTDRV.EXE program and stores the copy
as SMARTDRV.MSC. PATCH_SD works only if
the size of SMARTDRV.EXE is equal to 45145 bytes.
To modify SMARTDrive to recognize CorelCDX:
1. Enter the following at the command prompt: PATCH_SD.
2. Check your AUTOEXEC.BAT file to ensure that CorelCDX
is loaded before SMARTDrive. If SMARTDrive is loaded
first, it won't find, and therefore cache, CD-ROM drives.
Since SMARTDrive is loaded after CorelCDX, you can't
use the CorelCDX /UNLOAD command.
3. Disable the CDXCACHE by setting the CorelCDX command
line option /XMSSIZE to 0. If you don't disable this
cache, both CDXCACHE and SMARTDrive will cache data,
using twice the necessary amount of extended memory.
4. Reboot your system to reinstall SMARTDRV.EXE.
3. Configuring CorelCDX
-------------------------
CorelCDX is configured using command line switches. Some
of these switches affect the caching features. For more
information, see the topic, "CorelCDX Caching".
The CorelCDX command syntax includes the path to the
location of CorelCDX and several switches. For example,
the following command indicates that CorelCDX is located
in the CORELDRV directory:
C:\CORELDRV\CORELCDX [options]
/CACHE:pt;dir;data
Defines the number of cache buffers allocated, in blocks,
to the path table, directory, and data caches, respectively.
Typically, the /M option is used rather than /CACHE. However,
the /CACHE option allows more precise control over the use
of allocated cache buffers. If both the /CACHE and /M options
are used, the /CACHE values override the /M value.
You can set path table and directory caches from 2 to 64
blocks. Each block requires 2K. The data cache can be set
from 2 to 64 blocks. The size of each block is determined
by the /DATABLK option.
Minimum, maximum, and alignment requirements may require
that the actual number of buffers differ slightly from
those you specify.
/DATABLK:sectors
Defines the number of 2K sectors assigned to each data
cache block. You can set this value to 1, 2, 4, or 8 sectors.
If you don't specify a size, the data cache block size is
set to 2 sectors by default.
This option is useful for applications that read data from
compact discs in contiguous segments.
Unless you're using CDXCACHE, setting the /DATABLK value
to 1 disables read-ahead caching. However, an additional
4K of conventional memory is required.
The internal read-ahead caching logic of some CD-ROM
drives may be adversely affected by changing the
default data cache block size.
/D:name...
Displays the required name of the CD-ROM device driver.
If you enter more than one CD-ROM device driver name,
separate each name with a comma and remove any blanks
between names.
If you're using Corel's DOS CD-ROM device drivers,
names are numbered starting from MSCD001. If you're
using Corel's NetWare CD-ROM device drivers, names
are numbered starting from MSCD099.
If driver names aren't included in the command line,
CorelCDX will try to locate and initialize the CD-ROM
device drivers named, by default, MSCD001 or MSCD099.
/E:value
Indicates whether code, data, or cache buffers are
to be stored in expanded memory. This option doesn't
affect cache buffers used by CDXCACHE.
The option /E:1 loads code and data into expanded
memory. Only a small footprint remains resident in
conventional memory. This option may be incompatible
with some CD-ROM applications; for example, those
that perform absolute disk reads into expanded
memory buffers.
The options /E:2 and /E load only cache buffers
into expanded memory.
The option /E:3 loads code, data, and cache buffers
into expanded memory. In rare cases, this value may
cause problems when you try to read data from a CD-ROM
drive. Some applications, when loaded in expanded
memory, may create memory conflicts. If you experience
problems, change the option to either /E or /E:2.
If cache buffers are loaded in expanded memory, a small
amount of conventional memory may be allocated to store
required tables, and so on. To make the most efficient
use of allocated memory, the driver may slightly increase
the number of specified cache buffers.
/FILES:num
Sets the maximum number of CD-ROM files that can be
open at the same time. Each file requires approximately
16 bytes.
If you don't specify this option, the maximum number
of open files is set to the same value as the FILES
command in your CONFIG.SYS file.
/L:letter
Indicates the drive letter, from A to Z, at which
CorelCDX starts assigning letters to CD-ROM drives.
If the letter you specify isn't available, the next
available drive letter is used. This option is useful
for software that requires specific drive letters for
CD-ROM drives.
/M:buffers
Indicates the approximate number of cache buffers
allocated, in blocks, for all CD-ROM drives.
Typically, the /M option is used rather than /CACHE.
However, the /CACHE option allows more precise control
over the use of allocated cache buffers. If both the
/CACHE and /M options are used, the /CACHE values
override the /M value.
/NOFILE
Prevents CorelCDX from looking for a CRLSCSI.INI file
for configuration options. This file isn't required
when you configure CorelCDX using command line switches.
/SHARE
/S
Permits CD-ROM drive sharing with Windows for Workgroups.
/VERBOSE
/VB
Displays information onscreen about CorelCDX as it's
loading during the system boot.
/XMSBLOCK:size
Sets the maximum size of read request in sectors that
will be cached by CDXCACHE. The cache performance may
benefit from larger values. However, the cache may fill
up more quickly. A size of 4 is recommended.
/XMSPAGE:sectors
Indicates the number of sectors per cache page, which
determines the read-ahead operations. This option affects
only CDXCACHE.
The value of 4 is recommended for smaller cache sizes;
it's more important to cache separate disk reads than
to perform read-aheads. Use the value 8 for larger cache
sizes; more data is stored in one operation.
/XMSSIZE:size
Indicates the size, in kilobytes, of the CDXCACHE cache.
Set the size to 0 to disable this cache.
A size of -1 creates a default cache size equal to
one-quarter of the free extended memory. You can
also set the size to a value from 64 to 16384.
