Interface classification of a hard disk

From the overall point of view, the hard disk interface is divided into IDE, SATA, SCSI, Fibre Channel, M2-SATA, M2-Nvme and SAS seven, IDE interface hard disk is mostly used in household products, but also partly used in the server, SCSI interface hard disk is mainly used in the server market, and Fibre Channel is only in the high-end server. It's expensive. SATA is a new type of hard disk interface that is still in the market popularization stage and has broad prospects in the home market. Under the large category of IDE and SCSI, you can separate a variety of specific interface types, and each has different technical specifications, with different transmission speeds, such as ATA100 and SATA; Ultra160 SCSI and Ultra320 SCSI represent specific hard disk interfaces, and their speeds differ greatly.

IDE
IDE's English full name is "Integrated Drive Electronics", that is, "electronic integrated drive", its original intention is to refer to the "hard drive controller" and "disk body" integrated together. The integration of the disk with the controller reduces the number and length of cables for the hard disk interface, increases the reliability of data transmission, and makes hard disk manufacturing easier because hard disk manufacturers no longer need to worry about whether their hard disk is compatible with controllers produced by other manufacturers. Hard disks are also easier for users to install. The IDE interface technology has been continuously developing since its birth, and its performance has been continuously improved, and its low price and strong compatibility have created a position that other types of hard disks can not be replaced.
IDE represents a type of hard disk, but in actual applications, people are also used to using IDE to call the earliest IDE type hard disk ATA-1, this type of interface has been eliminated with the development of interface technology, and then the development of more types of hard disk interface, For example, ATA, Ultra ATA, DMA, Ultra DMA and other interfaces belong to IDE hard drives.
The IDE hard drives have the following transmission modes: PIO(Programmed I/O) mode, Driect Memory Access (DMA) mode, and Ultra DMA(UDMA) mode.
The biggest disadvantage of the PIO(Programmed I/O) mode is that it consumes an extremely large amount of CPU resources. IDE interfaces running in PIO mode have data transfer rates ranging from 3.3MB/s(PIO mode 0) to 16.6MB/s(PIO Mode 4).
Direct Memory Access (DMA) mode is divided into Single-Word DMA and Multi-Word DMA. Single-Word DMA mode has a maximum transfer rate of 8.33MB/s, and Multi-Word DMA(Double Word) can reach 16.66MB/s.
The biggest difference between DMA mode and PIO mode is that DMA mode does not run with excessive dependence on CPU instructions, which can achieve the effect of saving processor operating resources. However, due to the emergence and rapid popularity of Ultra DMA modes, these two modes were immediately replaced by UDMA.
Ultra DMA Mode (UDMA) is a standard referenced under the Ultra ATA format, using the 16-bit Multi-Word DMA mode as a benchmark. One of the advantages of UDMA is that in addition to the advantages of DMA mode, it also uses Cyclic Redundancy Check (CRC) technology to enhance the performance of debugging and debugging during data transfer.
Since the introduction of the Ultra ATA standard, its interface has applied DDR(Double Data Rate) technology to double the transmission speed, and has been developed to Ultra ATA/100, its transmission speed of up to 100MB/s.

SCSI
SCSI English full name "Small Computer System Interface" (small computer system interface), is a completely different interface with IDE (ATA), IDE interface is the standard interface of ordinary PC, and SCSI is not specifically designed for the hard disk interface, It is a high-speed data transmission technology widely used in minicomputers. SCSI interface has a wide range of applications, multitasking, large bandwidth, low CPU usage, and hot swap and other advantages, but the high price makes it difficult to popularize as IDE hard disk, so SCSI hard disk is mainly used in medium and high-end servers and high-end workstations.

Fibre channel
The English spelling of the Fibre Channel is Fiber Channel, and the SCSI interface, the Fibre Channel is not originally designed for the hard disk interface technology, is specially designed for the network system, but with the storage system speed requirements, it is gradually applied to the hard disk system. Fibre Channel disk is developed to improve the speed and flexibility of multi-disk storage systems, and its appearance greatly improves the communication speed of multi-disk systems. Fibre Channel provides the following features: hot swappability, high-speed bandwidth, remote connection, and large number of connected devices.
Fibre Channel is designed for multi-disk system environments such as servers and can meet the high data transfer rate requirements of high-end workstations, servers, mass storage subnetworks, and peripherals for bidirectional, serial data communication through hubs, switches, and point-to-point connections.

SATA
The hard disk that uses the SATA (Serial ATA) port is also called the serial hard disk, which is the mainstream trend of the future PC hard disk. In 2001, the Serial ATA Committee composed of Intel, APT, Dell, IBM, Seagate, and Mactor formally established the Serial ATA 1.0 specification. In 2002, although the related equipment of Serial ATA was not officially listed, But the Serial ATA Committee has taken the lead in establishing the Serial ATA 2.0 specification. Serial ATA adopts serial connection mode, and serial ATA bus uses embedded clock signal, which has stronger error correction ability. Compared with the past, the biggest difference is that it can check transmitted instructions (not only data), and automatically correct if errors are found, which greatly improves the reliability of data transmission.

SAS
Serial Attached SCSI (SAS), Serial attached SCSI, is a new generation of SCSI technology, and the popular Serial ATA(SATA) hard disk is the same, are using serial technology to obtain higher transmission speed, and by shortening the connection line to improve the internal space. SAS is a new interface developed after the parallel SCSI interface. This interface is designed to improve the performance, availability, and scalability of the storage system and to provide compatibility with SATA hard drives.
SAS interface technology is backward compatible with SATA. Specifically, the compatibility of the two is mainly reflected in the compatibility of the physical layer and the protocol layer. At the physical layer, SAS interface and SATA interface are fully compatible, SATA hard disk can be directly used in the SAS environment, from the interface standard, SATA is a sub-standard of SAS, so SAS controller can directly control SATA hard disk, but SAS can not be directly used in the SATA environment. The SATA controller cannot control SAS disks. At the protocol layer, SAS consists of three types of protocols, which are used for data transmission according to different connected devices. The Serial SCSI protocol (SSP) is used to transmit SCSI commands. The SCSI Management Protocol (SMP) is used to maintain and manage connected devices. The SATA Channel protocol (STP) is used to transfer data between SAS and SATA. Therefore, with the cooperation of these three protocols, SAS can be seamlessly combined with SATA and some SCSI devices.

The Backplane of the SAS system can connect both dual-port, high-performance SAS drives and high-capacity, low-cost SATA drives. Therefore, SAS drives and SATA drives can coexist in the same storage system. However, it should be noted that SATA systems are not SAS compatible, so SAS drives cannot be connected to SATA backplanes. Because of the compatibility of the SAS system, users can use hard disks with different interfaces to meet the capacity or performance requirements of various applications, so that there is more flexibility in the expansion of the storage system, so that the storage device can maximize the investment benefit.

In the system, each SAS port can be connected to a maximum of 16256 external devices, and SAS takes direct point-to-point serial transmission mode, transmission rate of up to 3Gbps, it is estimated that there will be 6Gbps and even 12Gbps high-speed interface in the future. The interface of SAS has also been greatly improved, and it offers both 3.5-inch and 2.5-inch interfaces, so it can be adapted to the needs of different server environments. SAS relies on SAS extenders to connect more devices, and the extenders are mostly 12 ports, but according to the product development plan of the board manufacturer, there will be 28 and 36 port extenders introduced in the future to connect SAS devices, host devices or other SAS extenders.
Compared with the traditional parallel SCSI interface, SAS not only has a significant increase in interface speed (the mainstream Ultra 320 SCSI speed is 320MB/sec, while SAS has just started to reach 300MB/sec, and will reach 600MB/sec or more in the future), but also because of the use of serial cables, Not only can you achieve a longer connection distance, but also improve anti-interference ability, and this thin cable can also significantly improve the heat dissipation inside the chassis.