This article shows a very detailed introduction to hard drive controller which is the interface device between computers and hard disk driver.

Hard Drive Controller – Operating Principle


Hard disk controller, known as the adapter of hard disk driver, is the interface device between computers and hard disk driver. Hard disk controller is used to receive and interpret the computer order, and then send various control signals to hard disk adapter. Also, it detects the hard disk driver status. Data is written in the disk and read from the disk by hard disk controller according to the disk data format.

There are many types of hard disk controller, but the basic components and the operating principle are approximately the same. It consists of control logical circuit connected to a computer system bus, microprocessor, decoding and encoding circuit used to accomplish the separation of read-in data and compensation of write-in data, data error detection and correction circuit, logical circuit used for controlling the data transmission, serial and parallel conversion as well as formatting in accordance with the computer orders, read-only memory used for storing basic input and output program of disk and buffer for data exchange etc. 

Hard Disk Controller – IDE Controller

Serial Port

IDE controller is usually produced in the mainboard. It can support up to 4 hard disks. The maximum speed of IDE controller is 66Megabytes ( MB ) per second, but many IDE controllers can only reach 33Megabytes per second. IDE controller has several variants, and the most common one is ATA ( Advanced Technology Attachment ). Invented by IBM, ATA is the second controller placed in hard disk, and it has largely increase the data transmission speed. ATA-3 and ATA-4 whose performance has been further improved are being widely used by audio workstation. If you don’t know which kind of controller is used in computer, you can refer to the manuals of mainboard and keyboard.

ATA can be classified in following types.

  1. ATA-1: ATA-1 is the original hard disk controller. It is the same with IDE. 
  2. ATA-2: ATA-2 is often regarded as the fast ATA ( FASTATA ) or enhanced IDE ( EIDE ). EIDE, first introduced by Western Digital, utilizes new BIOS and allows computer to manage hard disk with a capacity over 504MB. FastATA, simultaneously introduced by Quantum and Seagate, supports hard disk over 504MB and transmits data faster. Four devices can be connected to it, including CD-ROM and tape drive.
  3. ATA-3: ATA-3 is released following the introduction of ATA-2. But there are not many improvements in performance. Usually, ATA-3 is equivalent to EIDE or FastATA.
  4. ATA-4: ATA-4, also known as UltraTAT or UltraDMA, includes ATAPI4 regulations. ATAPI, short for Advanced Technology Attachment with Packet Interface, allows CD-ROM and tape drive to share ATA bus with ATA hard disk. ATA-4 is the most used controller in computer nowadays.
  5. ATA-5: ATA-5 is a developing regulation that can support a transmission speed over 66MB and enhance the reliability by improving internal algorithms. ATA-5 demands new UDMA80 cable and new mainboard will support ATA-5.
  6. Apple-ATA: Many Macintosh computers like G3 and G4 also execute IDE, EIDE or UDMA regulations, which allow users to utilize any standard PC hard disk after being formatted again.
Note: When you need to recover data from a formatted hard drive on Mac, please go to this page

Data Handling Capacity

The specifications related to handling capacity are derived with the introduction of various ATA specifications.


The maximum of data handling capacity is 66MB/s.

ATA/100 is similar to ATA/66, but its maximum data handling capacity is 100MB/s. Mainboard and hard disk must support ATA/100 at the same time. Some PCI cards produced by third party can help computers run ATA/100 drive.

Hard Disk Controller – SCSI Controller

SCSI Controller 

SCSI ( pronounced like scuzzy ) is a very advanced hard disk controller, but it is hard to popularize because of its high price. SCSI can support devices like multi-hard disk, CD-ROM and scanner, and it also can connect as many as 30 devices and peripherals by daisy chain. It is the most suitable for studio which needs enormous capacity. SCSI controller, traditionally faster than IDE, can reach the speed of 160MN/s, and the new controller being developed can even reach 320MB/s. Just like IDE and SCSI, they have different versions. SCSI is the first choice if your DAW needs the best performance, specification of 24bit/96Khz or 24bit/192KHz and mass storage of data.

Two devices are needed to use SCSI in the system: SCSI controller, which usually performs as a PCI card, and SCSI devices like hard disk and CD-ROM. They need SCSI cable to connect. The final choice is up to your budget and the work nature.

The Relevant Regulations of SCSI

SCSI-1: SCSI-1 is the original regulation and first SCSI standard in 1986. It is allowed to connect up to 7 devices, and the maximum transmission speed is 5MB/s. This is epochal at that time.

SCSI-2: SCSI-2, also called Fast SCSI, has been improved a lot on the basis of SCSI-1, and it hasn’t been widely used till 1994. SCSI-2 streamlines some unreasonable options and enhances the reliability. The transmission speed is increased to 10MB/s.

Fast Wide SCSI: Fast Wide SCSI is a type of SCSI-2. Its bus width has been doubled to 16bit and the maximum transmission speed is 20MB/s. 14 devices can be connected to this kind of controller.

Ultra SCSI: Ultra SCSI, a type of SCSI-2 as well, utilizes original 8-bit bus. The maximum transmission speed is 20MB/s, and the number of devices which can connect to a single controller is still 7.

Ultra Wide SCSI: Ultra Wide SCSI is also known as Wide Ultra SCSI. Just like Fast Wide SCSI, it utilizes 16-bit bus and the maximum transmission speed is 20MB/s. One controller can connect 14 devices.

Ultra2 SCSI: Ultra2 SCSI utilizes 8-bit bus. But the internal clock speed has been doubled, and the maximum transmission speed is 40MB/s. The number of devices connecting to a single controller is still 7.

Wide Ultra2 SCSI: Wide Ultra2 SCSI is the fastest SCSI in a period of time. It utilizes 16-bit bus. The internal clock speed has been doubled and the maximum transmission speed is 80MB/s. One controller can connect 7 devices.

Ultra3 SCSI: Ultra3 SCSI, also known as SCSI160, is a rather fast SCSI standard. The maximum transmission speed is 80MB/s when a 32-bit PCI slot controller is utilized, and the maximum transmission speed can reach 160MB/s when a 64-bit PCI slot controller is utilized. One controller can connect 14 devices.

Ultra320 SCSI: Ultra320 SCSI is the new SCSI standard and is just put into application. The maximum transmission speed is 160MB/s when it utilizes a 32-bit PCI slot controller, and the maximum transmission speed is 320MB/s when it utilizes a 64-bit PCI slot controller. SCSI320 uses 16-bit bus and it can be compatible with SCSI160.

Hard Disk Controller – SAS Technology

Built-in SATA Hard Disk Controller

SAS ( Serial Attached SCSI ) is a new technology of hard disk attachment. It combines the advantages of current parallel SCSI and serial attached technology ( like fiber channel, SSA, IEEE1394 and InfiniBand ), sets serial communication as the protocol infrastructure, adopts SCSI-3 extended instruction set and can be compatible with SATA devices. It is a multi-level storage devices stack. And SAS disk is a disk adopting this interface technology. According to the industry prediction, SAS disk will take place of SCSI and become the main type of disk very soon.

SAS Characteristics

1. Better Performance

The technology of spot to spot reduces the address conflicts and the deceleration of daisy chain;

It provides special signal channel to each device to ensure the maximum bandwidth;

Data operation under full duplex ensures the most effective data handling capacity.

2. Simple Cable Link

Thinner cable matches smaller connector.

3. Better Scalability

It can connect more disk devices simultaneously.

Since serial SCSI ( SAS ) is the spot-to-spot structure, except for the increase of performance, the bandwidth has been increased as each device is connected to appointed data channel. SAS cable structure save space, and thus, the cooling and ventilation capacity of SAS hard disk server have been improved. In general, large parallel cable will bring electronic interference, and SAS cable structure can solve this problem. What’s more, SAS structure has good scalability. It can connect at most 16384 disk devices.

Serial SCSI (SAS ) hard disk utilizes the same interface with S-ATA. But SAS can use more signals and SAS hard disk cannot be connected to S-ATA hard disk controller. As SAS is the universe interface, it can support SAS and S-ATA. SAS controller can support SAS and SATA disk. SAS controller supports S-ATA hard disk because S-ATA uses the signal subset of SAS controller.

Switch Interface

Early SAS hard disk utilizes 2.5 inches package. By doing so, rack server can support more hard disks. Some manufacturers have released 3.5 inches SAS hard disk. The rotation speed of early SAS hard disk is 10000RPM, while SAS hard disk with the speed of 15000RPM has emerged. Compared with SCSI hard disk with the same rotation speed, SAS hard disk possesses the equal or better performance. Serial interface reduces the cable size and allows faster transmission speed and the data transmission speed of SAS hard disk can reach 3.0Git/sec.

Each SAS cable has 4 cables, 2 for input and 2 for output. SAS can conduct data read and write at the same time, and data operation of full duplex increases the data handling capacity.

As a new storage interface technology, SAS is considered as the replacement of SCSI. This is because SAS is not only functionally comparable with fiber channel, but also compatible with SATA. The strengths of SAS are mainly reflected on following aspects.


It can be compatible with SATA and save cost for users.


A SAS domain can connect up to 16384 devices directly.

Excellent Performance

The performance of spot-to-spot structure will be improved along with the increase of the number of ports.

More reasonable cable design

More effective cooling can be provided in high-density environments.

Four basic indicators are often used to weigh a technology, namely performance, reliability, scalability and cost. Recalling the history of serial disk technology development, from fiber channel, to SATA, and then SAS, several technologies have their own strengths. Serial storage technology, which is the first technology of fiber channel can meet the storage requirements of high performance, high reliability and high scalability.

But its price is expensive. Although the price of SATA hard disk is really cheap, it is mainly used in near-line-storage and non-critical application. After all, it is unsatisfactory in terms of performance. SAS should be regarded as an all-rounder. It can support SAS and SATA hard disk to satisfy the different cost-effective storage requirements. And it is a resolution of high performance, high reliability and high scalability.

Hard Disk Controller – Common Errors

Parallel Port

The most common failure of hard disk is the guided fault, namely hard disk failing to start. When guided fault occurs, system will send many error prompts. Making sense of these prompts can be helpful to deal with hard disk problems.

1. Error prompt: HDD controller failure

Explanation: hard disk driver controller failure

Reason: when you start the computer, driver cannot complete the operations within the specific time after POST program ( BIOS automatic detection program ) sends a seek order to driver. And this leads to time-out error. If this case happens, maybe your hard disk is damaged.

2. Error prompt: HD controller failure

Explanation: hard disk controller failure

Reason: this kind of failure is classified to hardware failure. This is because after POST program sends a reset order to controller, the interrupt response is not given out by controller within a specific period of time. The reasons may be relative to the controller damage or failure of cable plugging. In addition, controller failure is also relevant to the validity of hard disk parameter.


Explanation: no curing BASIC system and system downtime.

This error often appears on 486 and previous computer. Only on very old computer will the prompt appear. When the system is started, the role of master boot program is to find an active partition ( which can be started ) from the four entries of partition table. If there is no active partition in the hard disk, system cannot find the place to guide operating system. So, system has to suspend and call the BASIC program solidified in BIOS. And if there is no curing BASIC, this error appears. It can cause shutdown. Therefore, the simplest repair method is to set an active partition in the hard disk with FDISK. Then, if the computer has no curing BASIC program, this error will not happen again.

Note: Let’s see how to fix the problem if a partition has been marked as active by mistake
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