Editing Macintosh Quadra 900

{{Infobox computer
| name         = Macintosh Quadra 900
| image        = [[File:Apple Macintosh Quadra 700 and 900.jpg]]
| caption      = Macintosh Quadra 900
| manufacturer = Apple Computer, Inc.
| type         = Personal Computer
| release_date = October 21, 1991
| discontinued = May 18, 1992
| price        = US$7,200
| cpu          = Motorola 68040 @ 25 MHz
| memory       = 4 MB RAM (expandable to 256 MB)
| storage      = 160 MB or 400 MB SCSI hard drive, 1.44 MB floppy
| display      = DB-15 video output, 1 MB VRAM (expandable to 2 MB)
| sound        = 8-bit stereo output, mono input
| dimensions   = 18.6" H × 8.9" W × 20.6" D (47.2 × 22.6 × 52.3 cm)
| weight       = 36.8 lbs (16.7 kg)
| os           = System 7.0.1 – Mac OS 8.1
| predecessor  = [[Macintosh IIfx]]
| successor    = [[Macintosh Quadra 950]]
| model        = M4200
}}
The '''Macintosh Quadra 900''' is a personal computer designed and manufactured by Apple Computer, released on October 21, 1991.<ref>{{cite web |url=https://everymac.com/systems/apple/mac_quadra/specs/mac_quadra_900.html |title=Macintosh Quadra 900 Specs |publisher=EveryMac.com |access-date=2026-02-10}}</ref> It was introduced alongside the [[Macintosh Quadra 700|Quadra 700]] as the first computers in the Quadra family using the [[Motorola 68040]] processor.<ref>{{cite web |url=https://support.apple.com/kb/SP238 |title=Macintosh Quadra 900: Technical Specifications |publisher=Apple |access-date=2026-02-10}}</ref>

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 [[Macintosh Quadra 950|Quadra 950]], which features a 33 MHz processor and improved graphics support.

== Architecture and Processor ==

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 ==

=== RAM Configuration ===

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.<ref>{{cite web |url=https://en.wikipedia.org/wiki/Macintosh_Quadra_900 |title=Macintosh Quadra 900 |publisher=Wikipedia |access-date=2026-02-10}}</ref>

Standard configuration shipped with 4 MB of RAM.

=== ROM and System Software ===

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 ===

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 ==

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 ==

The Quadra 900 features:
* 3.5mm stereo output jack
* 3.5mm mono input jack
* 8-bit audio

== Input/Output and Expansion ==

=== Port Configuration ===

* 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 ===

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 ===

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 ==

The Quadra 900 uses a mid-tower case measuring 18.6 inches (47 cm) tall. The case design was shared with the [[Macintosh Quadra 950|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 ==

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 ==

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

== Troubleshooting ==

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

== Technical Details ==
<templatestyles src="Template:StyledTable/styles.css" />

=== System Architecture at a Glance ===
{| class="wikitable styled-table" style="width:90%; text-align:center;"
! 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 ==

The official Apple Service Source documentation for this model:

<pdf width="800" height="500">File:Quadra_900.950.ws_95.pdf</pdf>

== See Also ==

* [[Macintosh Quadra 700]] – Desktop Quadra released the same day
* [[Macintosh Quadra 950]] – Direct successor with 33 MHz processor
* [[Macintosh IIfx]] – Predecessor high-end Macintosh

== References ==
<references />

[[Category:Apple Vintage Computers]]