# direct-attached storage

> external computer storage, accessed directly by a single host over a local computer bus and/or interface (as opposed to a network)

**Wikidata**: [Q918468](https://www.wikidata.org/wiki/Q918468)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Direct-attached_storage)  
**Source**: https://4ort.xyz/entity/direct-attached-storage

## Summary
Direct-attached storage (DAS) is external computer storage accessed directly by a single host via a local computer bus or interface, rather than through a network. It serves as a form of auxiliary memory, utilizing devices such as hard disks connected through interfaces like USB or IEEE 1394. This storage architecture is distinct from network-based solutions like storage area networks (SANs) and network-attached storage (NAS).

## Key Facts
*   **Definition:** External storage accessed directly by a single host over a local bus/interface.
*   **Classification:** Subclass of auxiliary memory and external storage.
*   **Connectivity:** Utilizes connectors including USB and IEEE 1394 (FireWire); SCSI is considered a replaced entity in this context.
*   **Components:** Uses hard disks and computer interfaces; RAID configuration is rarely used.
*   **Alternatives:** It is the opposite of network-attached storage (NAS) and storage area networks (SAN).
*   **Aliases:** Also known as DAS, 直接连接的存储设备, and 直接附加存储.
*   **Academic IDs:** ACM Classification Code (2012): 10003174; Microsoft Academic ID: 154883912; Encyclopedia of China ID: 32811.

## FAQs
### Q: How does direct-attached storage (DAS) differ from network-attached storage (NAS)?
A: DAS is accessed directly by a single host over a local bus or interface, whereas NAS and storage area networks (SANs) are accessed over a network.

### Q: What hardware interfaces does DAS use?
A: DAS connects via local computer buses and interfaces, primarily USB and IEEE 1394. SCSI is listed as a replaced entity for this storage type.

### Q: Is DAS considered internal or external memory?
A: DAS is classified as external storage and auxiliary memory, meaning it is not directly accessible by the CPU but is accessed via input/output channels.

## Why It Matters
Direct-attached storage matters because it provides a fundamental, non-volatile storage solution that expands a computer's capacity without the complexity or latency of network infrastructure. As a form of auxiliary memory, it bridges the gap between a computer's primary memory and network-based systems, allowing for direct input/output communication with a single host.

By utilizing standard interfaces like USB, DAS offers a straightforward method for deploying additional storage capacity. It serves as the architectural opposite of network-attached storage (NAS) and storage area networks (SAN), representing the baseline for dedicated, host-specific data retention.

## Notable For
*   **Direct Access:** Distinct from network storage, it is accessed directly by a single host.
*   **Interface Usage:** Relies on local bus connections like USB and IEEE 1394 rather than network cables.
*   **Auxiliary Role:** Functions as non-volatile auxiliary memory accessed via I/O channels.
*   **Architecture:** Specifically excludes the use of RAID in most configurations (noted as "rarely").

## Body
### Definition and Classification
Direct-attached storage (DAS) is defined as external computer storage that is accessed directly by a single host computer. This access occurs over a local computer bus or interface, distinguishing it from storage solutions that require a network connection. Structurally, it is a subclass of **auxiliary memory**—non-volatile memory not directly accessible by the CPU—and **external storage**.

### Technical Specifications and Components
The system relies on specific hardware components and protocols to function:
*   **Connectors:** Standard connectors include **USB** and **IEEE 1394**. The **SCSI** interface is categorized as a "replaced entity" in the context of modern DAS usage.
*   **Devices:** It primarily utilizes **hard disks** (such as USB hard disks) and computer interfaces.
*   **Configuration:** While capable of using **RAID**, this configuration is noted as being rarely used in DAS applications.

### Comparison to Related Technologies
DAS is the architectural opposite of network-centric storage solutions. It contrasts directly with:
*   **Network-attached storage (NAS)**
*   **Storage area network (SAN)**

These alternatives rely on network connectivity, whereas DAS maintains a direct, dedicated connection to a single host machine.

## References

1. [Source](https://www.lenovo.com/gb/en/c/servers-storage/storage/das)
2. Freebase Data Dumps. 2013