The Lotus Multi-Byte Character Set (LMBCS) is a proprietary multi-byte character encoding originally conceived in 1988 at Lotus Development Corporation with input from Bob Balaban and others.^[1] Created around the same time and addressing some of the same problems, LMBCS could be viewed as parallel development and possible alternative to Unicode.^[1] For maximum compatibility, later issues of LMBCS incorporate UTF-16 as a subset.^[2][3]

Commercially, LMBCS was first introduced as the default character set of Lotus 1-2-3 Release 3 for DOS in March 1989^[1][4] and Lotus 1-2-3/G Release 1 for OS/2^[1] in 1990 replacing the 8-bit Lotus International Character Set (LICS) and ASCII used in earlier DOS-only versions of Lotus 1-2-3 and Symphony.^[5] LMBCS is also used in IBM/Lotus SmartSuite, Notes and Domino,^[1] as well as in a number of third-party products.

LMBCS encodes the characters required for languages using the Latin,^[6] Arabic, Hebrew, Greek and Cyrillic^[6] scripts, the Thai, Chinese, Japanese^[6] and Korean writing systems, and technical symbols.

Technically, LMBCS is a lead-byte encoding where code point 00_hex as well as code points 20_hex (32) to 7F_hex (127) are identical to ASCII^[1] (as well as to LICS).^[5]

Code point 00_hex is always treated as NUL character to ensure maximum code compatibility with existing software libraries dealing with null-terminated strings^[1] in many programming languages such as C.^[a] This applies even to the UTF-16be codes, where code words with the form xx00_hex are mapped to private-use codes with the form F6xx_hex during encoding in order to avoid the use of NUL bytes,^[7] and to escaped control characters, where 20_hex is added to the C0 (but not C1) control characters following the 0F_hex lead byte.^[7]

Code points 01_hex to 1F_hex, which serve as control codes in ASCII, are used as lead bytes to switch the definition of code points above 7F_hex between several code groups (similar to code pages) and at the same time determine either a single- or multi-byte nature for the corresponding code group.^[1]

For example, code group 1 (with group byte 01_hex)^[1] is almost identical to the SBCS code page 850, whereas code group 16 (with group byte 10_hex)^[1] is similar to the Japanese MBCS code page 932. Multi-byte characters can thus occupy two or three bytes.^[7][6]

In canonical LMBCS, each character starts with its group byte.^[1] To reduce the length, in optimized or compressed LMBCS a default code group or optimization group code can be defined on a per application or process basis (ideally chosen according to the highest likelihood of occurrence)^[1] and must be communicated to the interpreting code in some way (f.e. by specifying the corresponding "LMBCS-n" name).^[8] Thereby, the group byte can be omitted for these characters.^[1] Lotus 1-2-3 retrieves the optimization group code from the file header of the corresponding source file,^[7] whereas for Lotus Notes the optimization group code is fixed to be always 01_hex.^[2][7]

Without prefix byte the code points 32 (20_hex) to 127 (7F_hex) are interpreted as follows (corresponding to LMBCS codes 32 to 127):

LMBCS group 1 code points 128 (80_hex) to 255 (FF_hex) are identical to the corresponding code points in code page 850 (DOS Latin-1), whereas code points 1 (01_hex) to 127 (7F_hex) are defined according to the following exception list (corresponding to LMBCS codes 256 to 383):

LMBCS group 2 code points 128 (80_hex) to 255 (FF_hex) are identical to the corresponding code points in code page 851 (DOS Greek), whereas code points 1 (01_hex) to 127 (7F_hex) are defined according to the following exception list:^[f]

LMBCS group 6 code points 128 (80_hex) to 255 (FF_hex) are identical to the corresponding code points in code page 852 (DOS Latin-2), whereas code points 1 (01_hex) to 127 (7F_hex) are defined according to the following exception list:^[f]

• Compose key
• GB 18030
• Standard Compression Scheme for Unicode (SCSU)
• Symbol (typeface)
• Xerox Character Code Standard (XCCS)

• Born, Günter [in German] (December 2000) [1990]. "Kapitel 2. LOTUS 1-2-3-Format (WK3)" [Chapter 2. Lotus 1-2-3 WK3 format]. Dateiformate – Eine Referenz – Tabellenkalkulation, Text, Grafik, Multimedia, Sound und Internet [File formats – a reference – spreadsheets, text, graphics, multimedia, sound and internet] (PDF) (in German). Bonn, Germany: Galileo Computing. ISBN 3-934358-83-7. Archived (PDF) from the original on 2016-11-29. Retrieved 2016-11-28. (Includes some information about LMBCS and Lotus system ranges.)
• "LMBCS tables". User's Guide – 123 Release 4 for Windows (Fax). Lotus Development. 1995 [1994-01-01]. CHAPTER: Appendix A Using the Lotus Multibyte Character Set. Fax 10955. Retrieved 2016-12-06.
• "Entering LMBCS characters". User's Guide – 123 Release 4 for Windows (Fax). Lotus Development. 1995 [1994-01-01]. CHAPTER: Appendix A Using the Lotus Multibyte Character Set. Fax 10954. Retrieved 2016-12-06.
• Lotus Support. "Notes from Support: SMTP MTA International Character Sets". IBM developerWorks. IBM. Archived from the original on 2016-12-08. Retrieved 2016-12-08.
• Character Translation Files (.CTF) by Notes 2.x and Country Language Service (.CLS) files by Notes 3.0 and higher contain information about LMBCS translation into other codepages [2] [3]

• Berntrop-Bos, Lars (2014-07-10). "Blast from the past: LMBCS tables for Windows, OS/2, Unix and Macintosh". Archived from the original on 2016-11-26. Retrieved 2016-11-26.