identify Ampex harddisk

Ampex

PYXIS-7 5.4MB (ST-412, 90.0/??KB/??) MFM, CHS 320x2x17, 5.25"
PYXIS-13 10.9MB (ST-412, 90.0/??KB/??) MFM, CHS 320x4x17, 5.25"
PYXIS-20 16.3MB (ST-412, 90.0/??KB/??) MFM, CHS 320x6x17, 5.25"
PYXIS-27 21.8MB (ST-412, 90.0/??KB/??) MFM, CHS 320x8x17, 5.25"