What are common Hard Drive terms?

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Problem: What are common Hard Drive terms?



Hard Drive Terms
ATA (at Attachment) The official standard name for IDE.
DMA (Direct Memory Access) A technique that allows a device to write to memory without going through the processor.
EIDE (Enhanced IDE) An improved version of IDE.
IDE (Integrated Device Electronics) The base standard interface for PC hard drives. It’s equivalent to data—the standards committee’s name for it.
RPM (Revolutions per minute) A measure of a drive’s speed. A higher number means a faster drive.
SCSI (Small computer system interface) A device connection used for hard drives that’s a bit more complicated but often faster than IDE. Choose this type for advanced multimedia work or for servers. Faster versions of this include Fast, Wide, Ultra, and LVD (low-voltage differential) SCSI.

SCSI interface overview
Interface Bus width Clock speed Max. throughput Max. cable length Max. number of devices
SCSI 8-bit 5 MHz 5 MB/s 6 m 8
Fast SCSI 8-bit 10 MHz 10 MB/s 1.5-3 m 8
Wide SCSI 16-bit 10 MHz 20 MB/s 1.5-3 m 16
Ultra SCSI 8-bit 20 MHz 20 MB/s 1.5-3 m 5-8
Ultra Wide SCSI 16-bit 20 MHz 40 MB/s 1.5-3 m 5-8
Ultra2 SCSI 8-bit 40 MHz 40 MB/s 12 m 8
Ultra2 Wide SCSI 16-bit 40 MHz 80 MB/s 12 m 16
Ultra3 SCSI 16-bit 40 MHz DDR 160 MB/s 12 m 16
Ultra-320 SCSI 16-bit 80 MHz DDR 320 MB/s 12 m 16
SSA 1 bit 400 Mbit 80 MB/s 25 m 96
FC-AL 1 bit 4 Gbit 400 MB/s
per direction; full duplex
 ? 127
iSCSI Dependent upon IP network  ??
SAS 3 Gbps 1 bit N/A 300 MB/s
per direction; full duplex
6 m 16,256 (128 per expander)
SMART (Self-monitoring analysis and reporting technology) A system that alerts you if the drive is about to fail so that you can back it up.
Ultra ATA An improved version of ATA that uses Ultra DMA. Equivalent to Ultra DMA, UDMA, ATA-33 (or ata-66, even faster), or DMA-33 (again, or -66).
UltraDMA or UTMA An improved version of DMA that’s twice as fast as the original. Equivalent to Ultra ATA.
SATA – Serial ATA interfaces, also known as SATA/150, run at 1.5 gigahertz. Serial ATA uses 8B/10B encoding at the physical layer. This encoding scheme has an efficiency of 80%, resulting in an actual data transfer rate of 1.2 gigabits per second (Gbit/s), or 150 megabytes per second. The relative simplicity of a serial link and the use of LVDS allow both the use of longer drive cables as well as an easier transition path to higher speeds.
SATA II With the release of the NVIDIA nForce4 chipset in 2004, the clock rate was doubled to 3.0 GHz, for a maximum throughput of 300 MB/s. SATA II is usually both forward and backward compatible with SATA, allowing SATA hardware to interface with SATA II ports and vice versa. However, some systems that don’t support SATA speed autonegotiation may require that the drive’s speed is manually limited to 150 MB/s with the use of a jumper for a 300 MB/s drive.[1]

The 3.0 GHz specification has been very widely referred to as “Serial ATA II” (“SATA II”), contrary to the wishes of the Serial ATA standards organization that authored it. The official website notes that SATA II was in fact that organization’s name at the time, the SATA II specification being only one of many that SATA II defined, and suggests that “SATA 3Gb/s” be used instead. (The Serial ATA standards organization has since changed names, and is now “The Serial ATA International Organization”, abbreviated SATA-IO.)SATA-IO plans to further increase the maximum throughput of Serial ATA to 600 MB/s around the year 2007.SATA II is also sometimes referred to as SATA/300, continuing the line of PATA/100, PATA/133 and SATA/150
SAS Serial Attached SCSI (SAS) is a new generation serial communication protocol for devices designed to allow for much higher speed data transfers and is compatible with SATA. SAS uses serial communication instead of the parallel method found in traditional SCSI devices but still uses SCSI commands for interacting with SAS devices.

SAS supports up to 16,384 addressable devices in a SAS domain and point to point data transfer speeds up to 3 Gbit/s, but is expected to reach 10 Gbit/s by the year 2011. The SAS connector is much smaller than traditional parallel SCSI connectors allowing for small 2.5 inch drives.


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