The portion of the Unicode standard which describes the character codespace is known as the Universal Character Set (UCS). UCS is also published separately by the International Organization for Standardization as ISO/IEC 10646.

The UCS codespace consists of 17 planes, each containing 65,536 characters. These planes are listed below. Only Plane 0 is directly supported by OS/2.

Plane 0

(U+0000 - U+FFFF)
Basic Multilingual Plane (BMP). This plane covers most modern writing systems.

The first 256 codepoints of the BMP (U+0000 through U+00FF) map directly to ISO-8859-1, the ISO Latin-1 encoding; this corresponds to OS/2 codepage 819. On OS/2 systems, this fact is principally useful with respect to the basic ASCII character set (U+0020 through U+007F).

Plane 1

(U+10000 - U+1FFFF)
Supplementary Multilingual Plane (SMP). This plane is primarily used for historical or academic scripts, as well as notational characters which are rarely used in computing.

Plane 2

(U+20000 - U+2FFFF)
Supplementary Ideographic Plane (SIP). This plane is used for rare (mostly historical) Chinese ideographic characters.

Planes 3 - 13

(U+30000 - U+DFFFF)
Unassigned.

Plane 14

(U+E0000 - U+EFFFF)
Supplementary Special-Purpose Plane (SSP).

Planes 15 - 16

(U+F0000 - U+10FFFF)
Supplementary Private Use Area.

See the next two sections for a breakdown of the specific character sets assigned to each value range.