Flash can be written to either a word (8 or 16 bits) or a buffer (several words at a time). All chips support single-word writes, so it is always a conservative choice. More sophisticated chips such as Intel StrataFlash and AMD MirrorBit support buffered writes, which are significantly faster.
When consulting AMD's datasheets, don't confuse their "Unlock Bypass" write mode with their buffered write mode. The unlock bypass mode eliminates only the extra handshake between each word write. Real buffered write modes collect several words into an internal buffer and programs them in parallel.