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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 character-encoding scheme to represent the data in a Text, Memo, or Hyperlink 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 4,096 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.