Command: UHDD.SYS

  UHDD is a disk caching driver.


  DEVICE[HIGH] = [path] UHDD.SYS [/A] [/B] [/E] [/H] [/O] [/Q]
                 [/R15] [/R63] [/Snn] [/Z]


  UHDD usually needs only a /H switch to use HMA space and a /S switch
  to set its cache size, and a /O switch to enable DMA/Caching Overlap
  (best, for most systems!). All UHDD switches are:
  /A    Requests "alternate" addressing for "legacy" IDE controllers,
        01E8h/0168h for the first one, 01F0h/0170h for the second.
        /A is rarely needed. Without /A, the first "legacy" con-
        troller will use 01F0h/0170h and a second uses 01E8h/0168h
        as is usual for PC mainboards.
  /B    Sets a "basic" UltraDMA disk driver (no cache), using 128K of
        XMS as its buffer for I-O unsuited to UltraDMA. With /B,
        the /E /O and /S switches are ignored.
  /E    Does not use UltraDMA, for old 80386/80486 PCs that never had
        UltraDMA! UHDD "calls the BIOS" for disk I-O and caches
        data (as needed) after the BIOS is done. With /E, the /A
        /Q and /Z switches are ignored.
  /H    Puts most of the driver in "free HMA" space. To use /H, the
        driver must load from FDAUTO.BAT (not FDCONFIG.SYS), since
        FreeDOS provides no "free HMA" until FDAUTO is run.
  /O    Overlaps disk UltraDMA with caching tasks, for faster speed.
        Although preferred, /O may NOT work on old/odd/"cheap" PC
        mainboards unable to do UltraDMA and access XMS memory at
        the same time! Systems should be tested, using /O. If
        disk errors occur, but CD/DVD input via UDVD2 works fine,
        /O must NOT be used!
  /Q    Awaits "data request" before starting UltraDMA I-O transfers.
        /Q is rarely needed, only for old systems where the driver
        loads O.K. but seems unable to transfer data. /Q is NOT
        for use with Sabrent or other SATA-to-IDE adapters that do
        not emulate "data request"!
  /R15  "Reserves" 15-MB or 63-MB of XMS, for old DOS "game" programs
  /R63  which require XMS memory below 16- or 64-MB. The drivers
        must be able to reserve this memory, reserve their own XMS
        memory beyond that, and then "free" the 15/63-MB XMS. If
        not, the drivers display "XMS init error" and abort! /R
        for UDVD2 is ignored if it loads after UHDD, as UDVD2 will
        then share UHDD's XMS memory.
  /Snn  Requests the desired cache size, in megabytes of XMS memory.
        Values are any number from 5 to 4093 (4-GB). A minimum
        20-MB cache is recommended when possible, for best speed.
        If /S is omitted or invalid, a 20-MB cache is set. UHDD
        displays "XMS init error" and aborts, when not-enough XMS
        is free! If so, request a smaller cache.
  /Z    Moves protected-mode XMS data in 8K blocks (not 64K) for 486+
        CPUs and 4K blocks for slow 386 CPUs. For more /Z notes,
        see /Z for XMGR, above.


  UHDD is a disk caching driver that runs up to 10 BIOS disks of any type
  or size using up to 4 "Legacy" or Native-PCI UltraDMA controllers. It
  traps Int 13h I-O calls and caches data for disks, A: and B: diskettes,
  and other Int 13h drivers which load first. If loaded after UHDD, the
  UDVD2 driver (below) will call UHDD to cache CD/DVD data files. UHDD
  uses Read-Ahead for UltraDMA disks, and its /O switch will overlap disk
  UltraDMA and caching tasks. Using both is up to 20 % faster than older
  "UIDE" drivers! Write-Through caching is done (NO "delayed" output!).
  UHDD's cache uses XMS memory and holds up to 4 Gigabytes of data. Its
  /B switch also sets a basic UltraDMA disk driver (no cache) taking 128K
  of XMS as its buffer for I-O unsuited to UltraDMA. The basic UHDD can
  handle tests and other noncached work.
  For all switches in each driver, a dash may replace the slash and lower
  case letters may be used if desired.
  UHDD and UDVD2 are Closed-Source DOS drivers for PCs with an 80386+
  CPU (UHDD requires an 80486+ CPU) and using MS-DOS V5.0+ or a
  fully compatible variant.
  The latest UHDD and UDVD2 are Open Source device drivers for PCs with
  an 80386+ CPU and using FreeDOS, whereas at XMGR, RDISK it depends on
  the version number if it is Open Source or Closed Source.
  For more information and if you are in doubt, read "README.txt" in


  Comment: There are new closed source drivers for UHDD.SYS (=XHDD.SYS)
  and UVD2.SYS (=XDVD2.SYS) which may have other options. So please do
  not rely on the options in the examples!
  A) A small real-mode system that needs only XMS may use this
    CONFIG.SYS/FDCONFIG.SYS example file:
     DEVICE=C:\BIN\XMGR.SYS /Rnn              ;R if DOS "games" need it
       ..  Int 13h drivers cached by UHDD load now.
     DEVICE=C:\BIN\UHDD.SYS /S20 /H /O        ;Min. 20 MB recommended
     DEVICE=C:\BIN\UDVD2.SYS /D:BLURAY1 /H    ;Must load after UHDD
     DEVICE=C:\BIN\RDISK.COM /S5 /F           ;Optional. If not used,
                                              ; UHDD/UDVD2 can issue /F
       ..  Further CONFIG.SYS commands can be given here.
  B) Real-mode systems with V3.70+ UMBPCI and XMGR do not need the LOWDMA
     driver, as XMGR has an "I-O Catcher" for UMBPCI. This scheme takes
     NO low memory if /W can be used (MS-DOS etc.) or only 544 low memory
     bytes without /W (PC-DOS etc.). XMGR and other drivers load direct
     to UMBPCI "Shadow RAM"! Systems which permit multiple providers of
     upper memory (MS-DOS, PC-DOS, etc.) can also load an "EMM" driver as
     shown below, to map the B000-B7FFh "Monochrome Graphics" area as 32K
     more upper memory. For more SERIOUS protected-mode notes, please
     READ Section 6 below! An example CONFIG.SYS file is:
     DEVICE=C:\BIN\XMGR.SYS /W /Rnn            ;W only when permitted!
                                               ;R <= 15.5 MB with JEMM!
     DEVICE=C:\BIN\JEMM386.EXE I=B000-B7FF X=C800-EFFF ...   ;Optional
       ..  Int 13h drivers cached via UHDD load now
       ..  and can be loaded in UMBPCI upper memory.
     DEVICEHIGH=C:\BIN\UHDD.SYS /S200 /H /O    ;Fast 200 MB cache
     DEVICEHIGH=C:\BIN\UDVD2.SYS /D:CDROM1 /H  ;Must load after UHDD
     DEVICEHIGH=C:\BIN\RDISK.COM /S50 /F       ;Optional. If unused,
                                               ; UHDD/UDVD2 can issue /F
       ..  Further CONFIG.SYS commands can be given here.
  C) A protected-mode system with XMGR and an "EMM" driver can use XMGR's
     "boot", taking a minimum 304 bytes of low memory for a 24-entry "XMS
     Handles" table, plus any low memory the "EMM" driver may need. For
     more SERIOUS protected-mode notes, please READ Section 6 below! A
     CONFIG.SYS example file is:
     DEVICE=C:\BIN\XMGR.SYS /B /N24 /R15.5     ;24 Handle XMGR "boot"
                                               ;R <= 15.5 MB with JEMM!
     DEVICE=C:\BIN\JEMM386.EXE I=B000-B7FF ...
     DEVICEHIGH=C:\BIN\XMGR.SYS                ;Loads the runtime XMGR
       ..  Int 13h drivers cached by UHDD load
       ..  now and can load into upper memory.
     DEVICEHIGH=C:\BIN\UHDD.SYS /S400 /H /O /P ;Optimal 400 MB cache
     DEVICEHIGH=C:\BIN\UDVD2.SYS /D:MYDVD /H   ;Must load after UHDD
     DEVICEHIGH=C:\BIN\RDISK.COM /S125 /F      ;Optional. If unused,
                                               ; UHDD/UDVD2 can issue /F
       ..  Further CONFIG.SYS commands can be given here.
  In each example above, UDVD2 must load after UHDD, so UDVD2 will "find"
  UHDD in memory and call it for CD/DVD file caching.

  Users that need RDISK with a specific drive letter may delay loading it
  until AUTOEXEC.BAT is run. If /F or /G are also needed for DOS games,
  RDISK must issue them from AUTOEXEC, since it is then the last of these
  drivers to load. Whenever RDISK is used, AUTOEXEC.BAT must also issue
  commands to copy all RDISK programs and data up to the RAM-disk, as XMS
  memory is LOST when PCs shut down! Such copies require little time.

  If UHDD and RDISK will both run, users must balance how much XMS memory
  the drivers take. UHDD can set a 400-MB cache, as in example C above,
  and RDISK can request 125-MB of XMS for its programs, "fast" data files
  and compiler TEMP files. Such sizes should be optimal on most systems
  but can be adjusted up or down, as desired. All remaining XMS memory
  is left free for use by other programs. The basic "plan" is for RDISK
  to hold programs and high-speed files, while UHDD then caches "regular"
  data files. Properly balanced use of XMS memory will give a VERY fast
  DOS system!

See also:

  cc cash cleaner for uhdd

  Copyright © 2018 - 2022 Jack Ellis, updated 2022 by W. Spiegl.

  This file is derived from the FreeDOS Spec Command HOWTO.
  See the file H2Cpying for copying conditions.