What is a SCSI cable? Learn the definition, types (Centronics, HD50, VHDCI, 68-pin), connectors, and uses of SCSI cables in servers, RAID, and industrial systems in this complete guide.

Shenzhen, China (PRUnderground) July 22nd, 2026

A SCSI cable (which stands for “Small Computer System Interface”) is a special cable used for transferring data between a computer system/server and other devices (like hard drives, tape drives, RAID controllers, scanners, and printers). Rather than using a simple, point-to-point interface, the SCSI architecture utilizes a “bus” architecture which allows multiple devices (either 7 or 15, depending on the bus size) to share a common controller/channel as a single network.

The primary function of a SCSI cable is to provide a physical route for commands to travel from the host adapter to the devices attached. Over the many years that SCSI has gone from its initial version (SCSI-1) up to current versions such as SCSI-3 and Ultra320, the SCSI cable standards have been developed to carry increasingly wide buses of data (from 5 MB/s to 320 MB/s (theoretical and possibly 640MB/s), with a wider bus (from 8-bit to 16-bit), and to support a larger number of devices on a single cable due to more densely packed connectors.

Even though modern interfaces like SATA, SAS, and USB have replaced SCSI in many consumer products, the SCSI cable is still very important for traditional business storage solutions; for medical imaging, industrial control, and for data storage and archiving purposes. In these applications, the reliability of the SCSI cable and the ability to connect multiple devices to the same cable are the key features.

View our entire line-up of high-performance assemblies on our SCSI Cables store page, where we make both External SCSI and Internal SCSI types of cables for every generation of SCSI.

SCSI and the Cable Standards used to support it

The definition and form factors of SCSI cables began with the standards set by the SCSI interface (SCSI-1 through SCSI-3/Ultra320) during their rapid evolution from the 1980s to the early 2000s.

• SCSI-1 (1986): incorporated a large 50-pin Centronics (CN50) connector for all external devices, and a 50-pinIDC ribbon for all internal devices, and could support up to 5MB/s via a narrow 8-bit SCSI bus.
• SCSI-2 (1990) ​came with HPDB50 (HD50) external connectors and Thumbscrews/latch lock. The 68 Pin SCSI cable supports 16-bit Wide SCSI and Fast SCSI (10 MB/s).
• SCSI-3 (1995 onward): Led to Ultra, Ultra2, Ultra160, and Ultra320. The HD68 (HPDB68), VHDCI 68-pin and 80-pin SCA​ connectors all came at this time; as did the shift from SE (Single-Ended) to LVD (Low Voltage Differential) signaling, which improved noise immunity and increased the length of SCSI cables.
• Ultra320 (2002): The last of the big parallel SCSI formats, capable of speeds of 320 MB/s, required very precise impedance control and use of both active and passive termination techniques.

Each time the SCSI standards evolved, they also required that new cables be manufactured; originally using a flat ribbon cable with IDC terminations, and later moving to precision shielded round cables with Ferrite beads/cores for EMI suppression.

SCSI Cable Types Based on Their Connector Type and Intended Application

To describe a SCSI cable, you need to define its pin count (number of pins), shell type, and signaling. The following represent some of the most common forms of SCSI cables that you may come across:

1. Centronics SCSI cable (CN50)

The Centronics SCSI cable is thought to be the original version of the SCSI-1 connector. This connector has an oversized rectangular metal housing with a bail latch/wire clip locking mechanism and contains 50 pins arranged in two rows. Many older tape drives, scanners, and Mac/PC peripherals utilized this cable. Due to the large size of this connector, it was largely replaced by the HD50 in newer systems; nevertheless, it is still a critical connector to have for keeping legacy equipment running.

2. 50 Pin SCSI Cable (HPDB50, HD50)

The 50-pin SCSI cable is manufactured in HD50 (Half-Pitch DB50) configuration and is half the size of the Centronics connector because of 0.025″ (0.64mm) / 0.050″ (1.27mm) pitch between conductors, which is the spacing between individual conductors. These cables have thumbscrews to help hold the cable in securely and provide an external standard for narrow SCSI-2 devices. The 50-pin SCSI ribbon cable features a SCSI twist/loop section used to connect hard drives in a daisy-chain manner.

3. 68 Pin SCSI Cable (HD68 / HPDB68)

The 68-pin SCSI (HD68) cable doubles the number of conductors in a 16-bit Wide SCSI bus compared to the 50-pin (HD50). The HD68 cable also enables Wide SCSI speeds to reach 20 MB/s through 80 MB/s (Ultra2 LVD), as the HD50 cable does. The most common usage for this cable includes anything from external RAID arrays to tape libraries. The highest-quality HD68 cables provide individually shielded twisted pairs, which help reduce signal integrity issues, crosstalk, attenuation, and reflections at higher clock rates.

4. The VHDCI cable (Very High Density Cable Interconnect)

The VHDCI cable provides a solution for rack space limitations, as the VHDCI 68-pin connector has a pitch of 0.8mm and is almost half the size of HD68. This enables four VHDCI ports to occupy the equivalent space of one HD68 port on a PCI bracket. It is extremely common for multichannel RAID and SPI testers. The VHDCI Cable must conform to precision impedance control as required for Ultra160/Ultra320 speeds.

5. SCSI Ribbon Cable (Internal IDC)

The SCSI ribbon cable is a multi-conductor flat cable terminated on one end with an IDC (Insulation Displacement Connector or mass termination). They are available in both 50-pin and 68-pin configurations and connect internal SCSI drives to internal host adapters. A twist on the SCSI ribbon cable about an inch from the last connector should ensure proper termination, or “press-fit” termination, is supplied to the connector on a narrow SCSI bus. Shielded ribbon or custom IDC cable assemblies are typically used for internal Wide SCSI High Speed communication.

6. SCSI-2 Cable (Transitional Standard)

The term ‘SCSI-2 cable‘ is general for cables that meet the SCSI-2 standard. This mainly includes HD50 cables for narrow applications and HD68 cables for wide applications, which correspond to fast and wide SCSI. These cables help to make the transition between the large SCSI-1 Centronics cables and fast LVD cables in SCSI-3. Cables such as these were very commonplace in the 1990s workstations made by Sun, HP, and SGI.

7. MDR Cable within SCSI Contexts

The term MDR Cable or Mini Delta Ribbon, though commonly related to Camera Link and machine vision applications, comes in many forms, including 50-pin and 68-pin MDR variants. These latter two are often found in industrial Data Acquisition (DAQ) using the SCSI interface and for motion control applications. Due to its robust shielding and high-density contact points, the MDR Cable’s ‘Mini Delta Ribbon’ format is well-suited for use within a SCSI bus topology (daisy-chained) integrated into an automated testing environment.

Note on Cross-Compatibility

Make sure that when you are looking at pin counts and connectors, just because the pin count is the same (example: 50-pin Centronics versus 50-pin HD50), the connectors themselves are physically different and will not mate together. Additionally, a VHDCI Cable is not interchangeable with an HD68 SCSI Cable without using an adapter. To avoid mismatches, you should always verify the physical shape of the connector with the socket your device has.

Understanding External vs Internal SCSI Cables

The SCSI interface cable is divided into two distinct domains:

• External SCSI cable: round, shielded, includes male connectors, thumbscrews, or bail latches. Built to withstand EMI in data center racks. They should all include a ferrite bead/core (EMI suppression) and large amounts of strain relief. The most common types will include CN50, HD50, HD68, and VHDCI.
• Internal SCSI cable can be found in flat ribbon form with female IDC socket termination. Although shielded cables do exist, most of the inexpensive ones are unshielded. The emphasis for these types of cables is on maximizing space within an enclosure. Internal ribbon cables have the SCSI Ribbon Cable​ and custom IDC Cable​ harnesses. The SCSI twist/cable twist is what makes narrow internal ribbon cables unique.

Each cable must adhere to the length limitations and signal attenuation rules between narrow and wide buses (6 meters for SE and 12 meters for LVD), in addition to being properly terminated using either Active or Passive termination.

Signaling Types and the Importance of Matching Them in Cables

A SCSI cable must electrically match the signaling of the bus it is connected to:

• Single-Ended (SE): This was the first SCSI signal type; the signal is referenced to ground. Because the signal mode is single-ended, there is a limit to how far away from the bus the SCSI cable can be. Most older types of SCSI cables were typically single-ended: i.e., Centronics SCSI Cable and 50 Pin SCSI Cable.
• Differential (HVD): used mainly in harsh industrial environments, this is a rare type of SCSI signaling. HVD is not compatible with SE/LVD; attempting to use HVD with SE/LVD will damage both signal interfaces.
• LVD (Low Voltage Differential) standardized the Ultra2, Ultra160, and Ultra320 SCSI interfaces; it used controlled-impedance cables (28 AWG twisted pair cables with at least a braided overall shield) to preserve the signal’s integrity at 320 MB/s while minimizing the effects of crosstalk and reflections.

Not using an impedance-controlled ribbon cable with an Ultra320 LVD SCSI bus might result in slower speeds due to link negotiation failure, or it might cause the bus to become unstable. For this reason, when you are defining the exact requirements for a SCSI internal ribbon cable, or the exact requirements for a shielded external SCSI cable, the impedance of the cables becomes very important.

Regular Application for SCSI Cable

The Use of SCSI Cables Today: Although SCSI is an old technology, many sectors still use SCSI cable because they support multiple devices in a daisy-chained configuration and offers a high-reliability cable solution.

• Legacy Storage in Enterprises – banks, hospitals, and government archives still operate with RAID arrays and tape libraries like LTO and DLT, using 68-pin SCSI or VHDCI cables.
• Medical Imaging – CT scanners and MRI machines commonly employ SCSI-2 cable or Centronics SCSI cable proprietary interfaces, which cannot be changed to another technology due to the lack of appropriate interfaces.
• Refrigeration equipment’s automated control system utilizes MDR and IDC cable types for SCSI applications that must support high data transfer rates with minimal electrical noise.
• Post Production: For this application, legacy SCSI drives are typically used for storing audio sample libraries and for creating backups on tape.
• Vintage computer restorations: Restoring Sun SPARCstations, Amiga, or Macintosh SE/30 machines can only be done using a genuine 50-Pin SCSI Cable (CN50 or HD50) and a SCSI Ribbon Cable.

In addition to the above products, the D-SUB collection of cables we offer will help with your legacy interface requirements, as they share common chassis space with serial and/or parallel port connections.

Building Features of a High-Quality SCSI Cable

There are several aspects to consider when choosing/buying a SCSI cable, and these are the most important:

• The cable’s impedance must be controlled. For LVD and Ultra320, this means the impedance must be about 132 ohms between the differentials.
• External cables need a dual shielding technique: foil wrap and tinned copper braid overall.
• High-speed ribbon cables can have twisted pairs. The twisting of pairs of wires should be such that each signal/ground pair is twisted using 28 AWG/30 AWG wires to reduce crosstalk between adjacent signals.
• The plating of the connectors must be either a gold flash or 30 microns of gold on contact surfaces to prevent corrosion.
• Strain Relief: Boots are molded in a round shape to be applied over the round cables, and the boots are reinforced at the header points of the IDCs that terminate onto a ribbon cable.
• Ferrite Cores: One (1) ferrite bead/shield (EMI suppression) on the outside of your external SCSI cable should be used in order to comply with FCC/CE requirements.
• Twist Section: There must be proper placement of the SCSI twist on your extremely narrow ribbon cables to correctly terminations.

Conclusion: SCSI Cables Still Matter

Let’s take a look at what a SCSI cable is. It’s much more than an ordinary bundle of connectors and wires. It has been developed over decades as a precise engineering of storage and industry. Many different types of SCSI cables have been developed over the years, ranging from the thick, large Centronics 50-pin SCSI cables up to the very sleek, compact, and high-density VHDCI Cables, and from the flat ribbon cable SCSI up to the much more robust shielded LVD 68 Pin SCSI Cable.

Learning the differences in SCSI cabling (SCSI-1 Centronics vs. SCSI-2 HD50 vs. SCSI-3 VHDCI), the type of signals (Single Ended/SE vs. Differential/Diff vs. Low Voltage Differential/LVD) that can be sent over each type of signal, and knowing the difference between the three types of terminations (Active vs. Passive vs. Forced Perfect Termination) becomes very important when maintaining existing legacy equipment or when considering purchasing cables for a twenty-plus-year industrial equipment life specification.

The type of SCSI cable you choose will guarantee the proper functioning of your Small Computer System Interface (SCSI-1 / SCSI-2 / SCSI-3 / Ultra320) bus with minimal disruption of signals and no loss due to reflections, attenuation, and crosstalk. This can apply whether you are purchasing a SCSI-2 cable for use on an older computing setup, trying to find a 50 Pin SCSI Cable for connecting an old reel-to-reel tape machine, a 68 Pin SCSI Cable at very high speeds connecting up items in a RAID enclosure, or using a SCSI Ribbon Cable for connecting storage internally within a server due to its more flexible construction.

Discover our precision-engineered products of SCSI Cable. We offer the best solutions to maintain connectivity for all of your mission-critical applications, including VHDCI Cable, MDR Cable, Centronics SCSI Cable, 50 Pin SCSI Cable, 68 Pin SCSI Cable, SCSI Ribbon Cable, IDC Cable, and D-SUB Cable.

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