Microsoft Real-Time Compression Interface (MRCI; pronounced "mercy")
provides a means for application programs and system utilities to compress
and decompress data.

It is normally installed as part of DBLSPACE.BIN file which is loaded at
boot time (see DoubleSpace Overview), but it may exist as ROM-based,
hardware-assisted server installed via ROM-Scan at system powerup.

See: INT 2fH 4a12H (see if MRCI is installed; get entry addr, etc.)
INT 1aH b001H (check for ROM-based MRCI server)

MRCI Fn 0001H (compress data)
MRCI Fn 0002H (decompress data)
MRCI Fn 0020H (incrementally decompress data)
MRCI Fn ffffH (deinstall server; not used)

MRCI API Error/Return Codes (codes returned by these fns)

MRCInfoRec structure
MRCRequestRec structure

Notes:   In order to use MRCI fns, you must obtain the API entry address
(and a MRCInfoRec used in every call) via INT 2fH 4a12H.

  The decompression services require knowledge of the original
(uncompressed) size of the data.

  Pragmatically, the uses of these fns are limited.  Since you
can assume that a disk compression system such as DoubleSpace
is installed, there is no reason to compress data for storage
on a local hard disk.

You might want to use MRCI for storing backup data to diskette
or perhaps for sending data across a network (or other
bandwidth bottleneck, such as a modem line).  Msbackup uses
MRCI fns to compress backup data.

  One novel idea is to use MRCI to compress screen data for
temporary storage in RAM.  For instance, a 4K text-mode screen
typically compresses to a few hundred bytes.

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Microsoft Real-time Compression Interface (MRCI)