Hard Drives (ATA-4 to SCSI) By Tyler and Kevin
ATA-4 • ATA-4 introduced Ultra DMA to hard drives. • It used bus mastering to achieve faster speeds. • 3 different modes in ATA-4 Ultra DMA mode 0: 16.7 MBps Ultra DMA mode 1: 25.0 MBps Ultra DMA mode 2: 33.3 MBps
INT13 Extensions • Originally the ATA-1 standard allowed up to 137 GB drives • The BIOS at the time only supported 504MB drives • LBA temporarily fixed this but it had a maximum of 8.4GB • Phoenix technologies came up with the Interrupt 13 (INT13) extensions which solved this
ATA-5 • ATA-5 used an 80-wire cable instead of the old 40-wire cable. • Included 2 more modes: Ultra DMA mode 3: 44.4 MBps Ultra DMA mode 4: 66.6 MBps
ATA-6 • Hard drive size flew up with ATA-6. • The new limit to the interface was increased by more than 144 petabytes • T13 gave the new standard a less-silly name, calling it ATA/ATAPI-6 or simply ATA – 6.
Serial ATA • Serial connection for hard drives • Speeds increased • Better air flow in case because of thin cords.
SCSI • SCSI stands for small computer system interface. • They were used for hardware and peripherals like: hard drives, printers, and high end tape back up machines.
SCSI IDs • SCSI IDs are assigned to every SCSI device on a number system of 1-15. • There is no order for these and can skip around. • These are how the host comunicates with each SCSI device.
SCSI Chains • SCSI Chains are chains of SCSI devices that all work together and connect to a host adapter. • All SCSI Chains must be terminated
Termination • The SCSI chains need to be terminated to prevent the signal from bouncing off of the end of the chain and the end devices will read the signal multiple times. • Most devices in the PC have their own termination built in. • With out termination, the chain will be like chaos.