The document discusses four main types of computer hard drives: 1) Parallel ATA (PATA) drives were the original type and used parallel signaling. 2) Serial ATA (SATA) drives transfer data faster using serial signaling and have thinner, more flexible cables. 3) Small Computer System Interface (SCSI) drives are faster, more reliable, and better for large data storage and movement. 4) Solid state drives (SSD) have no moving parts, provide faster access, are more durable and shock resistant, and use less power than traditional hard drives.