About compressing the data in a Text, Memo, or Hyperlink field (MDB)

 Note   The information in this topic applies only to a Microsoft Access database (.mdb).

Microsoft Access 2000 or later uses the Unicode (Unicode: A character encoding standard developed by the Unicode Consortium. By using more than one byte to represent each character, Unicode enables almost all of the written languages in the world to be represented by using a single character set.) character-encoding scheme to represent the data in a Text (Text data type: In a Microsoft Access database, this is a field data type. Text fields can contain up to 255 characters or the number of characters specified by the FieldSize property, whichever is less.), Memo (Memo data type: In a Microsoft Access database, this is a field data type. Memo fields can contain up to 65,535 characters.), or Hyperlink (Hyperlink data type: A data type for an Access database field that stores hyperlink addresses. An address can have up to four parts and is written using the following format: displaytext#address#subaddress#.) field. Unicode represents each character as two bytes, so the data in a Text, Memo, or Hyperlink field requires more storage space than it did in Access 97 or earlier, where each character is represented as one byte.

To offset this effect of Unicode character representation and to ensure optimal performance, the default value of the Unicode Compression property for a Text, Memo, or Hyperlink field is Yes. When a field's Unicode Compression property is set to Yes, any character whose first byte is 0 is compressed when it is stored and uncompressed when it is retrieved. Because the first byte of a Latin character — a character of a Western European language such as English, Spanish, or German — is 0, Unicode character representation does not affect how much storage space is required for compressed data that consists entirely of Latin characters.

In a single field, you can store any combination of characters that Unicode supports. However, if the first byte of a particular character is not 0, that character is not compressed.

Data in a Memo field is not compressed unless it requires 32 bytes or less of storage space after compression. As a result, the contents of a Memo field might be compressed in one record, but might not be compressed in another record.

Applies to:
Access 2003