Black Box 4/BlackBox.cdr/textinfo/alltips.arj/1305.TXT

Text File | 1991-11-26 | 6.0 KB | 114 lines

Document 1305
MEMORY USE

Initials:
    MDC
        11/2/91
        DRDOS 6.0

Keywords:
    MEM
        MEMORY
        EMM386.SYS
        EXTENDED
        EXPANDED
        LENDING
        EMS
        XMS

Description:
        When using the EMM386.SYS device driver, you may notice that the
        MEM command can display a memory report that seems to show more
        memory available than exists on your computer. For example,
        consider the following EMM386.SYS device driver line on a
        computer with 3,072 Kbytes of Extended memory:

        DEVICE=C:\DRDOS\EMM386.SYS /F=AUTO /K=AUTO /B=FFFF /R=AUTO

        This line has the effect of converting all Extended memory into
        Extended via XMS and EMS (expanded) memory. The resulting MEM
        report might show that the computer has 3,072 Kbytes of Extended
        memory and 3,072 Kbytes of EMS memory under the "Total Bytes"
        column, with 2,864 Kbytes of Extended via XMS memory and 2,864
        Kbytes of EMS memory under the "Available" column as shown below.

        / Memory Type -------- Total ---------- Available ---\
        |                  |                |                |
        | Conventional     |    (    60K )  |    (   626K )  |
        | Upper            |    (    96K )  |    (    79K )  |
        | High             |    (    64K )  |    (    18K )  |
        | Extended         |    ( 3,072K )  |    (     0K )  |
        | Extended via XMS |        N/A     |    ( 2,864K )  |
        | EMS              |    ( 3,072K )  |    ( 2,864K )  |
        \----------------------------------------------------/

        To understand this, it might be helpful to view the total
        Extended memory available on a computer as comprising a dynamic
        pool of memory. This memory can be viewed as dynamic because it
        is available to be accessed either as Extended via XMS memory or
        as EMS (expanded) memory depending on the "/K" setting on the
        EMM386.SYS device driver. In the case shown above, "/K=AUTO"
        tells EMM386.SYS to allow ALL of the Extended memory pool to be
        accessed as Extended via XMS memory and EMS memory in equal
        portions. The MEM command therefore shows both amounts of memory
        as being available because you or your applications might want
        to use a portion or all of the memory pool as either Extended
        via XMS memory or EMS memory. The "/K" switch can be used to put
        a limit on the amount of EMS memory to be created from the total
        memory pool. The following EMM386.SYS device driver line on the
        same computer with 3,072 Kbytes of Extended memory will limit
        the amount of EMS memory to be created from the total memory
        pool by setting the "/K" option to "/K=1024":

        DEVICE=C:\DRDOS\EMM386.SYS /F=AUTO /K=1024 /B=FFFF /R=AUTO

        This line will still cause EMM386.SYS to convert all of the
        memory pool into Extended via XMS, but it will limit the amount
        of EMS to 1,024 Kbytes. The resulting MEM report might show that
        the computer has 3,072 Kbytes of Extended memory and 1,024
        Kbytes of EMS memory under the "Total Bytes" column, with 2,864
        Kbytes of Extended via XMS memory still available but only 896
        Kbytes of EMS memory under the "Available" column as shown below.

        / Memory Type -------- Total ---------- Available ---\
        |                  |                |                |
        | Conventional     |    (   640K )  |    (   626K )  |
        | Upper            |    (    96K )  |    (    79K )  |
        | High             |    (    64K )  |    (    17K )  |
        | Extended         |    ( 3,072K )  |    (     0K )  |
        | Extended via XMS |        N/A     |    ( 2,864K )  |
        | EMS              |    ( 1,024K )  |    (   896K )  |
        \----------------------------------------------------/

        You will notice in both of the above examples, that there is a
        difference between the "Total Bytes" of Extended memory and the
        "Available" bytes of Extended via XMS memory and a similar
        difference between the "Total Bytes" of EMS memory and the
        "Available" bytes of EMS memory. This is due to the amount of
        "overhead" memory used by the EMM386.SYS software to convert the
        memory pool into both types of available memory.

        XMS memory is extended memory created by memory management
        software which conforms to the XMS specification developed by
        Lotus, Intel, and Microsoft. The DR DOS memory management
        software device driver (EMM386.SYS) fully supports this
        specification and, as a result, initially converts ALL of the
        computer's available extended memory into XMS extended memory.
        This is the reason that there is no "Extended" memory listed in
        the "Available" column of the DR DOS MEM report; it has all been
        converted to XMS memory by the EMM386.SYS device driver. This is
        also the reason why Extended via XMS lists as "N/A" under the
        "Total Bytes" column; XMS memory is created by a software device
        driver and is not present at boot time.

        Note:  EMS memory is listed with a specific value under the
        "Total Bytes" column by the MEM report unlike the Extended via
        XMS listing. EMS memory can be created by a software device
        driver (like EMM386.SYS alone) or can be created by EMS
        (LIM 4.0) hardware memory boards and their accompanying device
        driver. This specific value is intended to reflect this EMS
        memory created by the "/K" option on the EMM386.SYS device
        driver line or "hardware" EMS memory created by certain
        platforms, typically non- 386/386sx/486 platforms, which
        actually contain EMS (LIM 4.0) hardware.