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一款DOS下的RAM disk和disk cache组合在一起的工具。

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A simple test program CMBTEST.COM is supplied with the package. It
writes randomly to few files, deletes some of them etc. Its objective
is to convince You that memory allocation strategy used by COMBI-disk
is reliable. It may also be used to test write caching reliability.

Usage:
        CMBTEST <dirname> [<options>]
where <dirname> is name of directory (or drive) where CMBTEST  will
write the files - it may be a directory on a hard drive or COMBI's RAM
disk. <options> may be used if You want to run multiple test series.
(For more details see the source code CMBTEST.C) I suggest You to
run
        CMBTEST <COMBI's_RAM_drive_letter>:
and then
        CMBTEST <some_temporary_directory_on_hard_disk>
and compare the resulted files:
        COMP <path1>*.* <path2>
(<path1(2)> - pathnames of target directories). If all the "files
compare O'K" then there is no error and You may delete the files or
repeat the test with other options. Note: options must be the same for
both runs otherwise the files will be different.

You may also change the program if You have any new ideas how to
improve the test.


Control of operation.
--------------------

A control program COMBI.COM is supplied with the package. It allows
You to change cache or RAM disk options or change memory setting
without reconfiguring and rebooting. It also displays some statistic
information which may be helpful: current options, number of read/write
accesses to hard/RAM disk etc.

Usage:
        COMBI [+/-<mem_change] [<options>...]
where

<mem_change> -  amount of memory (Kbytes) to add to or release from
                COMBI-disk. If memory can't be reallocated by specified
                amount COMBI will report that.

<options>    -  a sequence of any of letters 'i', 'o', 'b', 'z', 'f',
                'r', 'n' which may be separated by spaces and/or
                followed by '-' which reverses the meaning of the
                option. Case of the letters is insignificant.

i            -  turn off delayed writing (write immediately) ('i-'
                turns delayed writing on),

o            -  turn cache on ('o-' - turn off),

b            -  enable background writing ('b-' - disable),

z            -  'freeze' cache - after freezing the sectors which are
                already in cache remain there (are not purged) while
                no new sectors are copied to cache. This may be useful
                e.g. if You have small cache and want to keep there
                only FAT and directories, then You might run "CHKDSK"
                (which reads the whole FAT and all the directories)
                and then "COMBI z". 'z-' returns cache to normal
                operation.

f            -  fix memory settings - this disables automatic
                reallocation of XMS memory to other programs.

n            -  tells RAM disk not to return 'sector not found' error.

r            -  resets all statistic counters (there is no 'r-'
                option).

"COMBI ?" displays quick help on parameters usage.

Source code COMBI.C and header file IOCTL.H are provided if You wish
to implement some control over COMBI-disk into Your applications


Compatibility.
-------------

COMBI-disk is compatible with:

  - MS-DOS versions 3.30 - 5.00 (if it were not it would be useless);

  - DR-DOS version 6.00 (version 5.00 was not tested);

  - Borland's Turbo-debugger TD386 (TD386 uses XMS memory released by
    COMBI-disk);

  - MS-WINDOWS;

  - DJGPP (GNU C++ compiler for DOS and GO32 DOS extender by
    DJDelorie), however LD (DJGPP linker) often runs into "Sector not
    found" error if some of object files are on RAM disk, usage of "N"
    installation option or "COMBI n" solves the problem;

  - many other programs.

COMBI-disk is incompatible with:

  - Maybe some multitasking programs (please report me about any
    incompatibilities).


Possible errors.
---------------

Sector not found - You tried to read a sector which does not contain
        any valid data (You haven't written into it yet or have  already
        deleted the file that occupied this sector). This never happens
        with the majority of programs. However, for some programs this
        occurs regularly. It is recommended to reply 'Ignore' to the
        'Retry, Ignore, Fail?' DOS prompt. If You are sure that this
        causes no errors You may specify option 'N' as one of
        installation parameters (or run "COMBI n"). In this case the
        'not found' sectors are also not read, but error status is not
        returned by COMBI-disk.

Warning! Once a file is deleted from RAM disk, it might not be correctly
unerased by any means. It's data is lost immediately.

Data error writing drive <RAM_disk> - this may happen when some XMS
        memory has been loaned to a program and that program also tries
        to write some files to RAM disk which has not enough memory for
        that. Suggested action - specify less amount of memory which
        COMBI-disk should release for other programs or configure the
        program to use other drive for temporary files.

        The same problem may arise if a program which used XMS memory
        terminated (or has been aborted) but not released memory. In
        this case COMBI-disk can't reallocate XMS memory back to the
        full size. It continues working but won't use the full buffer
        size for cache or RAM disk data.

        Other errors indicate that either COMBI-Disk internal data tables
are corrupt (e.g. overwritten by other program) or error in XMM driver
encountered.


Some hints.
----------

"TEMP" environment variable is used by MS-DOS as a directory for
temporary files, in particular when COMMAND.COM creates pipes
(e.g. "dir | sort | more" etc.).

"TMP" environment variable is used by many programs (e.g. Microsoft
compilers) as a directory for temporary files. So, setting TEMP and TMP
in AUTOEXEC.BAT to point to Your RAM disk may improve Your system
performance.

Many other programs also can take advantage of RAM disk - see their
manuals and configure them.

Using write caching is not very dangerous as it might seem. In fact,
when COMBI-disk is configured for background writing it often takes
less time to finish writing to hard disk than without write caching.
Moreover, while data is being written to disk You program continues
working and that saves You a lot of processor time. Enabling delayed
writing as a rule decreases number of hard disk accesses and hard disk
head motions. However, if You start a program that hooks INT 08 (timer)
and does not pass control to former INT 08 handlers (some games often
do so) it would be better if You disable delayed writes ("COMBI i")
before starting such a program and enable it later ("COMBI i-").

Freezing cache ("COMBI z") when it contains certain data may be useful
if COMBI-disk's buffer size is relatively small. E.g. Freezing cache
after "CHKDSK" results in faster search for a file or directory change,
freezing cache after run of some program (whose size is less than cache
size) results in faster loading of that program on future runs (while
other programs operate as without cache).


The name of the game.
--------------------

The name "COMBI" originates from "COMBInation" of such incompatible
(maybe even contradicting) at the first sight programs: RAM disk and
disk cache.


History information.
-------------------

Version 1.10 (01 Dec 1992):

Few bugs of version 1.00 were fixed. These include:
  - "Not enough memory" error under DOS other than MS v.5.00;
  - Very poor performance (worse than without cache) if VERIFY is set ON.

Now COMBI may use HMA under DR-DOS as well.
Performance of cache improved.
Write delay time increased from 5 to 18 clock ticks (1 sec).
Added Ctrl-Alt-Del handling to flush cache before reboot.
COMBI control program renamed from "CMBCTL" (which was hardly typeable
and hardly rememberable) to "COMBI", ANSI sequences are used to provide
color output.

Version 1.00 (08 Aug 1992):

A lot of new features added compared to previous versions: write
caching, reallocation of XMS memory, IOCtl interface to control
operation of COMBI-disk etc. Most of the code has been completely
rewritten. However, the main idea of dynamical memory reallocation
between RAM disk and disk cache remained the same.

Version 0.31 (15 Feb 1992):

Few minor bugs of version 0.30 fixed.
No other serious changes.

Version 0.30 (08 Nov 1991):

Performance of delete from RAM disk operations increased compared to
previous versions.

For certain configuration parameters (e.g. 320 /v 128 256) COMBI-Disk
created FAT larger than really needed. However, it was O'K for DOS 5.0
but led to errors with DOS 3.30.
      - Now it is fixed.

Version 0.20 (28 Oct 1991):

A bug has been discovered in version 0.10: RAM disk failed after an
attempt to write into boot sector and one or more sectors of FAT.
      - Now it is fixed.

DOS 4.0+ CHKDSK did not work with version 0.10 due to simplified
format of boot sector of RAM disk.
      - This is now corrected for MS-DOS 5.0 but some DOS versions need
        a certain text be written into boot sector (e.g. for IBM-DOS 4.0
	it is "RDV 1.20" at offset 3 of boot sector). If You are aware
        what You are doing, You may correct this problem for Your DOS.

Version 0.10 (13 Aug 1991):

The very first beta version of COMBI-Disk was version 0.01 (24 Jun 1991).
In this version (0.10) two minor bugs have been fixed:
        A. COMBI-Disk v.0.01 refused to work under DOS 3.30 - not
           just it couldn't but only refused.
        B. Device return codes were corrected.
No any serious bugs were discovered yet.


Future.
------

Here are some of my ideas about future developement of COMBI:

  - Caching of floppy disks;

  - Special version for 80386 processor (probably, usage of 80386
    instructions may increase performance);

  - Reallocation of XMS memory allocated to other programs is not
    currently supported (some of programs allocate XMS and then reallocate
    it to larger size) - that will be certanly done;

  - As regards usage of EMS instead of XMS, I'm not sure that it would be
    an advantage. However, if there is enough interest in that I'll implement
    EMS support;

  - Further improvement of performance.


----------------
If You have any questions, comments or find out any problems with
COMBI-disk usage please contact:

        Vadim V. Vlasov,
        Inst. for Nuclear Research of Russian Acad. Sci.,
        60th October Anniversary prospect, 7a,
        117312, Moscow, Russia.

        phone:    [phone]

        Internet: [e-mail]