RetroTechCollection

Macintosh Quadra 900

The Macintosh Quadra 900 is a personal computer designed and manufactured by Apple Computer, released on October 21, 1991.[1] It was introduced alongside the Quadra 700 as the first computers in the Quadra family using the Motorola 68040 processor.[2]

Macintosh Quadra 900
Macintosh Quadra 900
Specifications
ManufacturerApple Computer, Inc.
TypePersonal Computer
ReleasedOctober 21, 1991
DiscontinuedMay 18, 1992
Intro priceUS$7,200
CPUMotorola 68040 @ 25 MHz
Memory4 MB RAM (expandable to 256 MB)
Storage160 MB or 400 MB SCSI hard drive, 1.44 MB floppy
DisplayDB-15 video output, 1 MB VRAM (expandable to 2 MB)
Sound8-bit stereo output, mono input
Dimensions18.6" H × 8.9" W × 20.6" D (47.2 × 22.6 × 52.3 cm)
Weight36.8 lbs (16.7 kg)
OS / FirmwareSystem 7.0.1 – Mac OS 8.1
PredecessorMacintosh IIfx
SuccessorMacintosh Quadra 950
Model no.M4200

The Quadra 900 was Apple's first Macintosh in a tower case form factor, designed for use as a departmental server or high-end workstation. It was discontinued after approximately six months in favor of the Quadra 950, which features a 33 MHz processor and improved graphics support.

Architecture and Processor

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The Quadra 900 uses a Motorola 68040 processor running at 25 MHz with an integrated FPU and 8 KB of Level 1 cache. The 68040 is a full 32-bit processor with 32-bit data and address buses.

The system bus runs at 25 MHz. The clock input runs at 50 MHz, but the processor itself operates at 25 MHz (not clock-doubled).

Memory and Storage

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RAM Configuration

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The Quadra 900 has 16 30-pin SIMM slots supporting 80 ns RAM modules. RAM must be installed in groups of four identical SIMMs. Apple officially supported 64 MB, but third-party configurations achieved 256 MB using sixteen 16 MB SIMMs.[3]

Standard configuration shipped with 4 MB of RAM.

ROM and System Software

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The Quadra 900 includes a 1 MB ROM. It shipped with System 7.0.1 and supports Mac OS versions up to 8.1. It is the earliest Macintosh model capable of running Mac OS 8.

Storage Systems

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The system uses a SCSI interface for storage. Factory configurations included either no hard drive, a 160 MB, or a 400 MB SCSI hard drive. A 1.44 MB SuperDrive floppy drive is standard.

A front-facing 5.25" drive bay is available for a CD-ROM drive, tape backup, or SyQuest drive. Two additional internal 5.25" bays are available (three if no hard drive is installed).

Display and Graphics

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The Quadra 900 includes integrated video with a DB-15 connector. Standard VRAM is 1 MB, expandable to 2 MB via four 256K VRAM SIMM slots (80 ns).

Display resolutions supported:

  • 512×384 at 24-bit color (1 MB VRAM)
  • 640×480, 832×624, 1152×870 at 8-bit color (1 MB VRAM)
  • Up to 832×624 at 24-bit color (2 MB VRAM)
  • 1152×870 at 8-bit color (2 MB VRAM)

Additional displays can be supported via NuBus video cards.

Audio Capabilities

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The Quadra 900 features:

  • 3.5mm stereo output jack
  • 3.5mm mono input jack
  • 8-bit audio

Input/Output and Expansion

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Port Configuration

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  • 1× Apple Desktop Bus (ADB) port
  • 2× Serial ports (printer and modem)
  • 1× DB-25 SCSI port
  • 1× AAUI-15 Ethernet port (built-in)
  • 1× DB-15 video output
  • 3.5mm audio input and output jacks

Expansion Slots

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The Quadra 900 provides extensive expansion options:

  • 5× NuBus slots (three provide 15W, two provide 25W power)
  • 1× 68040 Processor Direct Slot (PDS)

Upgrade Options

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Apple offered a Quadra 950 logic board upgrade for $1,899 and a Workgroup Server 95 upgrade for $2,499. With the Power Macintosh Upgrade Card installed, the system runs at 50 MHz and identifies as "Power Macintosh 900" in System Profiler.

Design and Features

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The Quadra 900 uses a mid-tower case measuring 18.6 inches (47 cm) tall. The case design was shared with the Quadra 950 and Workgroup Server 95.

A three-position key-lock on the front panel provides security options:

  • Off – Machine cannot be powered up
  • On – Normal operation
  • Secure – Floppy drive and ADB port are disabled

Power supply provides up to 303W and accepts 100-240V AC at 50-60 Hz.

General Maintenance

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For detailed maintenance practices including cleaning, PRAM battery management, connector corrosion prevention, and voltage adjustments, refer to the dedicated Macintosh Quadra 900 General Maintenance page.

Capacitor Replacement Guide

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Detailed capacitor replacement guidelines can be found on the Macintosh Quadra 900 Capacitor Replacement Guide page.

Troubleshooting

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A comprehensive troubleshooting guide addressing power issues, video problems, and error codes is available on the Macintosh Quadra 900 Troubleshooting page.

Technical Details

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System Architecture at a Glance

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Sub-system Specification (Macintosh Quadra 900, 1991)
CPU Motorola 68040 @ 25 MHz
FPU Integrated
L1 Cache 8 KB
Bus width 32-bit data • 32-bit address
Bus speed 25 MHz
ROM 1 MB
RAM 4 MB standard, 256 MB maximum (16× 30-pin SIMM slots)
Video 1-2 MB VRAM, up to 1152×870
Sound 8-bit stereo output, mono input
Storage SCSI hard drive, 1.44 MB floppy
Expansion 5× NuBus, 1× PDS
Ports ADB, 2× Serial, SCSI, AAUI-15 Ethernet, DB-15 video

Service Documentation

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The official Apple Service Source documentation for this model:

See Also

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References

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  1. ↑ Macintosh Quadra 900 Specs, EveryMac.com—link(accessed 2026-02-10)
  2. ↑ Macintosh Quadra 900: Technical Specifications, Apple—link(accessed 2026-02-10)
  3. ↑ Macintosh Quadra 900, Wikipedia—link(accessed 2026-02-10)
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