Disk Interface - a Connection between Hard Disk and Host System

The disk interface is the connection of hard disk and host system. The function of disk interface is to transfer data between hard disk cache and host memory. Different hard disk interfaces have different connection speed between hard disk and computer. And in the whole system, the quality of the hard disk interface affects the operating speed and system performance directly.

Disk interface 1 From an overall perspective, hard disk interface is classified in five types: IDE, SATA, SCSI, SAS and Fiber Channel. Hard disks with IDE interface are mainly used in household products, partially for server. Hard disks with SCSI interface are primarily applied to servers. While Fiber Channel is only used in advanced servers as it is expensive. SATA is mainly applied to household market, and SATA, SATA II and SATA III are popular.

Under the big category of IDE and SCSI, a variety of specific interface types still exist. They have different technology specifications and different transmission rates.

CF (Compact Flash) interface is mainly used in small mobile devices. CF interface follows the ATA manufacture standard. However, the pin of it is not 68-pin, but 50-pin which is divided into two rows with 25-pin for each.

IDE is short for Integrated Drive Electronics, which is intended to refer the hard drive which integrates “hard disk controller” with “disk body”. This action reduces the cable number as well as length of the hard disk interface. Furthermore, by doing so the transmission reliability is enhanced and it becomes easier to produce because hard disk manufacturers don't need to be worried whether the hard disk is compatible with the controller produced by other manufacturers or not. And it is also more convenient for users to install the hard disk. IDE interface technology is being developed since the existence. With the characters of cheap price and good compatibility, IDE interface has been irreplaceable.

Disk interface 2

IDE represents a type of hard disk. While in actual use, IDE is used to refer to the earliest hard disk of IDE type – ATA-1. However, this type of interface has been eliminated with the advancement of interface technology and then more types of hard disk interface have been developed. For example, ATA, Ultra ATA, DMA and Ultra DMA interfaces all belong to IDE hard disk.

SCSI, short for Small Computer System Interface, is a kind of interface totally different from IDE (ATA). IDE interface is the standard interface of common PC while SCSI interface is not specially designed for hard disk, but is a high-speed transmission technology which is widely used in small-sized machine. SCSI has many advantages, including wide range of applications, multitasking, wide bandwidth, low CPU occupation rate and hot swap ability, and so on. But the higher price makes it difficult to popularize as IDE hard disk. So it is mainly used in medium and advanced servers and advanced workstations.

Fiber Channel
Just like SCSI interface, fiber channel is not the interface technology originally designed and developed for hard disk, but particularly for network system. But as the demand of storage system for speed is raised, it is gradually used to hard disk system. Fiber channel is developed to improve the speed and flexibility of hard disk storage system. And it has largely improved the communication speed of multi-drive system. The characteristics of Fiber Channel are: hot swap ability, high-speed bandwidth, long-distance connection, multiple connecting devices, and so on.

Fiber channel is designed for the multi-drive system environment like server to meet the demand for high-speed transmission rate needed by advanced workstations, servers, mass storage sub-network and peripheral for carrying out two-way and serial data transmission by concentrator, switch and point-to-point connection.

SATA interface is a trend for future PC hard disk. In 2001, Serial ATA 1.0 was officially established by Serial ATA Commission composed of Intel, APT, Dell, IBM, Seagate and Maxtor. In 2002, although the equipment relative to ATA series wasn't officially listed, the Serial ATA Commission established the specification of Serial ATA 1.0 in advance. Serial ATA uses serial connection, which makes use of embedded clock signal and so has a stronger error correction capability. Serial interface also has the advantages of simple structure and hot swap ability.

Disk interface 3

Serial ATA is a novel kind of hard disk interface which is totally different from parallel ATA. It is famous for applying serial mode in data transmission. Compared with ATA, SATA has many advantages. Firstly, SATA transmits data in the way of continuous serial, and only one-digit data can be transmitted each time. Secondly, Serial ATA has higher starting point and greater potential for development. The data transmission rate of Serial ATA 1.0 can reach 150MB/s, which is faster than 113MB/s of ATA (ATA/113). The data transmission rate of Serial ATA 2.0 can reach 300MB/s and the fastest speed of SATA will achieve 600MB/s in the future.

SATA II Interface
SATA II is developed on the basis of SATA. Its main characteristic is the external transmission rate has been further promoted from 1.5Gbps (150MB/sec) of SATA to 3Gbps (300MB/sec). In addition, it also has a series of technology characteristics, such as NCQ (Native Command Queuing), Port Multiplier, Staggered Spin-up, etc. So, interface which merely reaches 3Gbps of external transmission rate is not really SATA II.

The core technologies of SATA II are 3Gbps of external transmission rate and NCQ technology. NCQ technology can optimize the execution sequence of hard disk instruction to avoid reading and writing the different position of hard disk according to the instruction sequence mechanically. On the contrary, NCQ technology can sort the sequence after receiving instruction. The head after sorting can conduct addressing orderly and efficiently to avoid the consumption caused by constantly head moving to prolong the hard disk life. In addition, not all of SATA hard disk can support NCQ technology. NCQ technology doesn't support FAT file system, and it supports NTFS only.

As the SATA market is in disorder, the phenomenon that many SATA equipment providers abuse SATA II during market propaganda is intensified.

It is noticeable that when some earlier motherboards which only support 1.5Gbps Southbridge use SATA II hard disks, they may not find hard disk or encounter blue screen. But a majority of hard disk manufacturers have set a speed selection jumper on hard disk to force the 1.5Gbps or 3Gbps operating mode to be chosen (a minority of hard disk manufacturers set the operating mode through relevant tools or software).

When SATA hard disk sets RAID mode, usually drivers provided by motherboard chipset manufacturers are needed to be installed. But a few older SATA RAID controllers can set up RAID without loading drivers in some versions of Windows XP system with latest patch.