Memory
The memory tables are stored in memory and use hash indexes so that they are faster than MyISAM tables. The lifetime of the data of the memory tables depends on the up time of the database server. The memory storage engine is formerly known as HEAP.
Archive
The archive storage engine allows you to store a large number of records, which for archiving purpose, into a compressed format to save disk space. The archive storage engine compresses a record when it is inserted and decompress it using zlib library as it is read.
The archive tables only allow INSERT and SELECT statements. The ARCHIVE tables do not support indexes, so reading records requires a full table scanning.