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What Did Computers Use Before The USB Port Was Invented? - SlashGear

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  Published in Humor and Quirks on Saturday, October 18th 2025 at 22:35 GMT by SlashGear
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From Whirring Buses to Plug‑and‑Play: The Evolution of Computer Connectors Before USB

For decades before the ubiquitous “USB” port became the default way to connect keyboards, mice, printers, and flash drives, a patchwork of proprietary and standards‑based interfaces filled the world of personal computing. The journey from the early serial and parallel cables that required careful pin assignments to the streamlined, reversible connectors of today is a story of engineering ambition, market pressures, and the relentless push for simplicity. Below is a concise chronicle of the key technologies that bridged the gap between the original mainframes and the modern plug‑and‑play era, based on the information assembled in the SlashGear feature “What Did Computers Use Before USB Ports” and the linked resources.

1. Serial Ports – The RS‑232 Standard

Serial communication has its roots in the 1960s with the RS‑232 standard. It defined a bi‑directional point‑to‑point data link using a 25‑pin connector, though most early PCs used a 9‑pin version (DB‑9). Serial ports transmitted data bit‑by‑bit, with a line speed ranging from 110 bps to 115 200 bps, and required a host computer to handle the timing and error detection itself.

Key features:

• Low Pin Count: Only eight data bits plus optional parity, start, and stop bits.
• Versatility: Used for modems, mice (early mice used serial connections), and serial printers.
• Cable Length Limitations: Up to 50 feet (15 m) for reliable communication.

Despite being slow by modern standards, serial ports were prized for their robustness and simplicity. Most early personal computers—Apple’s Lisa, early IBM PCs, and the Commodore 64—featured serial ports as essential expansion slots.

2. Parallel Ports – The Printer’s Friend

Parallel ports came into play when higher throughput was needed. The IEEE 1284 standard, introduced in 1990, defined the printer port (commonly a 25‑pin D‑sub). Unlike serial ports, parallel ports could send eight bits simultaneously, increasing data transfer rates to 150 kB/s or more.

The parallel interface had several incarnations:

• Standard Parallel: Used mainly for printers, limited to about 60 cm of cable.
• ECP (Extended Capabilities Port): Added bidirectional communication, higher speeds (up to 2 MB/s).
• EPP (Enhanced Parallel Port): Optimized for faster device access, particularly useful for floppy drives.

Parallel ports were also used for external storage devices such as early external hard drives and CD‑ROM drives before the advent of SCSI and IDE.

3. PS/2 Ports – The Keyboard and Mouse Standard

The PS/2 port (named after the IBM Personal System/2 line) emerged in 1987 as a slim, 6‑pin mini‑DIN connector that handled both keyboard and mouse data. Its advantages over serial ports were twofold:

• Lower Pin Count and Cable Complexity: Two 6‑pin cables replaced the two separate serial cables.
• Reduced Interference: PS/2’s 8‑bit data transmission was more reliable for low‑speed peripherals.

While PS/2 ports eventually fell out of favor with the rise of USB, many professional keyboards and mice still rely on PS/2 for precise, latency‑free input.

4. SCSI – The High‑Performance Bus

The Small Computer System Interface (SCSI) standardized a complex bus that could support up to 16 devices (later extended to 33). Introduced in the 1980s, SCSI used a 50‑pin or 68‑pin connector (SCSI‑II and SCSI‑3 respectively) and supported a variety of devices: hard drives, CD‑ROMs, scanners, and even external modems.

Characteristics of SCSI:

• Multipoint Capability: Multiple devices shared a single bus, each assigned a unique ID.
• High Speeds: SCSI‑1 ran at 5 MB/s; SCSI‑2 at 10 MB/s; SCSI‑3 at 20 MB/s.
• Hot‑Swap and Daisy‑Chain: Devices could be swapped without powering down the system.

Because of its flexibility and performance, SCSI remained a favorite in servers, workstations, and high‑end consumer PCs up until the early 2000s.

5. IDE / ATA – The Mass‑Storage Standard

While not a peripheral connector in the same sense, Integrated Drive Electronics (IDE) or ATA (AT Attachment) defined how hard drives and optical drives interfaced with motherboards. IDE used a 40‑pin ribbon cable (later 80‑pin for higher data rates) and supported two devices per cable (master and slave).

Key points:

• Single Bus for Storage: Simplified installation of hard drives and CD/DVD drives.
• Low Pin Count: 40 or 80 pins for data, control, and power.
• Standardization: Most PCs used IDE until the transition to SATA.

6. Serial ATA (SATA) – The Modern Replacement

SATA emerged in the early 2000s, replacing IDE. It uses a slim 7‑pin data connector and a 15‑pin power connector. SATA supports:

• Higher Speeds: SATA I at 1.5 Gb/s, SATA II at 3 Gb/s, SATA III at 6 Gb/s.
• Hot‑Plugging: Drives can be swapped without shutting down the system.
• Simplified Cabling: Single cable per drive, reducing clutter.

SATA’s introduction paralleled the declining use of parallel and SCSI, as most devices now required only a single, high‑speed interface.

7. The USB Revolution – Why It Won

When the Universal Serial Bus (USB) standard debuted in 1996, it promised:

• Plug‑and‑Play: Devices auto‑detect and configure themselves.
• Power Delivery: Up to 2.5 W per port (USB 2.0) without needing external power.
• Universal Compatibility: A single connector type for keyboards, mice, flash drives, printers, and many other peripherals.

USB also introduced reverse polarity for safety and, later, USB 3.x for even higher bandwidth. By the early 2000s, USB had supplanted serial, parallel, PS/2, and even SCSI for most consumer devices.

8. Legacy and Modern Retrospective

Despite USB’s dominance, many legacy connectors still survive:

• Serial: Emulated via USB adapters or used in industrial equipment.
• Parallel: Rarely found in modern PCs, but used in specialized hardware.
• SCSI: Still used in high‑performance servers and storage arrays.
• PS/2: Preferred by gamers and professionals who demand the lowest latency.

The transition to USB did not erase these standards; instead, it integrated them into a larger ecosystem where adapters and virtual drivers ensure backward compatibility.

9. A Final Look Back

The SlashGear article and its cited sources illustrate a clear trajectory: from the low‑bandwidth, multi‑pin connectors of the early 1980s to the single, reversible, high‑speed USB port that has become a ubiquitous part of modern computing. Each technology reflected the era’s priorities—speed, simplicity, or versatility—and paved the way for the next step in peripheral evolution.

By understanding this lineage, users appreciate why today’s seemingly simple USB ports are the culmination of decades of engineering, standardization, and incremental improvement. Whether you’re plugging in a USB‑C flash drive or a legacy serial device via an adapter, you’re tapping into a history that spans from the first mechanical key switches to today’s lightning‑fast data links.