Editing Macintosh Plus

{{Infobox computer
| name         = Macintosh Plus
| image        = [[File:MacintoshPlus.jpg|250px]]
| caption      = Macintosh Plus
| manufacturer = Apple Computer, Inc.
| type         = Personal Computer
| release date = January 16, 1986
| discontinued = October 15, 1990
| price        = US$2,599
| cpu          = Motorola 68000 @ 8 MHz
| memory       = 1 MB RAM (expandable to 4 MB)
| storage      = 800 KB 3.5" floppy drive, External SCSI
| display      = 9" monochrome CRT (512×342 pixels)
| sound        = Monaural 8-bit, 22 kHz (4-voice)
| dimensions   = 13.6" H × 9.6" W × 10.9" D
| weight       = 16.5 lbs (7.5 kg)
| os           = System 3.0 – System 7.5.5
| predecessor  = [[Macintosh 512K]]
| successor    = [[Macintosh SE]]
| codename     = Mr. T
| model        = M0001A
}}
The '''Macintosh Plus''' is the third model in the Macintosh computer line, introduced on January 16, 1986, two years after the original Macintosh and a little more than a year after the Macintosh 512K, with a price tag of US$2,599.<ref>{{cite web |url=https://www.apple-history.com/plus |title=Macintosh Plus |publisher=Apple-History |access-date=2025-01-25}}</ref> The Apple Macintosh Plus features an 8 MHz 68000 processor, 1 MB of RAM, and an 800k disk drive in a beige or platinum all-in-one case with a 9" monochrome display. The Macintosh Plus was the first Macintosh to have a double-density 800k disk drive, a SCSI port to allow external expansion, and RAM slots to allow the RAM to be expanded beyond the pre-installed limit.<ref>{{cite book |last=Hertzfeld |first=Andy |title=Revolution in the Valley: The Insanely Great Story of How the Mac Was Made |publisher=O'Reilly Media |year=2005 |isbn=0596007191}}</ref>

Although the Macintosh Plus would become overshadowed by two new Macintoshes, the Macintosh SE and the Macintosh II in March 1987, it remained in production as a cheaper alternative until the introduction of the Macintosh Classic on October 15, 1990.<ref>{{cite web |url=https://www.computerhistory.org/timeline/1990/ |title=1990 Timeline of Computer History |publisher=Computer History Museum |access-date=2025-01-25}}</ref> This made the Macintosh Plus the longest-produced Macintosh model, having been on sale unchanged for 1,734 days, a record not surpassed until the second-generation Mac Pro in 2018. Originally, the computer's case was the same beige color as the original Macintosh, Pantone 453; however, in 1987, the case color was changed to the long-lived, warm gray "Platinum" color.<ref>{{cite web |url=https://lowendmac.com/1986/macintosh-plus/ |title=Macintosh Plus |publisher=Low End Mac |access-date=2025-01-25}}</ref>

== Architecture and Processor ==

The Macintosh Plus is powered by the '''Motorola MC68000''' microprocessor, operating at 8MHz.<ref>{{cite web |url=http://www.easy68k.com/paulrsm/doc/dpbm68k1.htm |title=Design Philosophy Behind Motorola's MC68000 |author=Thomas W. Starnes |publisher=BYTE Magazine |date=April 1983 |access-date=2025-01-25}}</ref> This 16/32-bit processor features:
* '''32-bit internal registers''' with 16-bit data bus
* '''16-bit address bus''' supporting up to 16 MB of addressable memory
* '''8 MHz clock speed''' providing improved performance over earlier Macintosh models

The processor features 32-bit register width, 16-bit data bus width, and 32-bit address bus width, though the Mac Plus motherboard had only 22 address lines connected, for a 4 MB maximum memory configuration.<ref>{{cite book |last=Williams |first=Gregg |title=The Apple Macintosh Computer |publisher=BYTE |year=1984 |isbn=0070705151}}</ref>

== Memory and Storage ==

The Macintosh Plus shipped with significant memory improvements over its predecessors:

=== RAM Configuration ===
* '''Standard RAM''': 1 MB of RAM standard, expandable to 4 MB
* '''Memory Architecture''': The Mac Plus was the first Apple computer to utilize user-upgradable SIMM memory modules instead of single DIP DRAM chips
* '''SIMM Slots''': Four SIMM slots were provided and the computer shipped with four 256 KB SIMMs, for 1 MB total RAM
* '''Maximum Capacity''': By replacing them with 1 MB SIMMs, it was possible to have 4 MB of RAM

=== ROM and System Software ===
The Mac Plus has 128 KB of ROM on the motherboard, which is double the amount of ROM in previous Macs; the ROMs included software to support SCSI, the then-new 800 KB floppy drive, and the Hierarchical File System (HFS). The Plus went through two ROM revisions during its general market relevance. The initial ROM was replaced after the first two months as it had a serious bug which prevented the Mac from booting if an external SCSI device was powered off. The second revision fixed a problem with some SCSI devices that could send the Mac into an endless reset at POST.

=== Storage Systems ===
It has what was then a new 3+1⁄2-inch double-sided 800 KB floppy drive, offering double the capacity of floppy disks from previous Macs, along with backward compatibility. The drive is controlled by the same IWM chip as in previous models, implementing variable speed GCR.

== Display and Graphics ==

The Macintosh Plus shipped with a 9-inch 512x342 display at 72 PPI (pixels per inch). The display specifications include:
* '''Screen Size''': 9 inches (23 cm) diagonal
* '''Resolution''': 512 × 342 pixels monochrome
* '''Display Type''': Built-in CRT monitor
* '''Pixel Density''': 72 pixels per inch

== Audio Capabilities ==

The Macintosh Plus utilized one 8-bit, 22 kHz built in speaker. No audio in support was provided on this model.

== Input/Output and Expansion ==

The Macintosh Plus introduced several important connectivity features:

=== SCSI Interface ===
The Macintosh Plus was the first Macintosh to have a SCSI port to allow external expansion. The SCSI bus on the Mac Plus is officially rated at 1.25 MBps/10 Mbps by Apple, although real world testing shows it to be barely over 0.26 MBps/2.1 Mbps – which is still 4x the speed of Apple's earlier floppy port hard drive.

=== Port Configuration ===
The back of the machine features ports, from left to right: Sound Out, Mouse, Floppy, SCSI, Printer, and Modem. The Macintosh Plus was the last classic Mac to have an RJ11 port on the front of the unit for the keyboard, as well as the DE-9 connector for the mouse; models released after the Macintosh Plus would use ADB ports.

== General Maintenance ==

Over time, Macintosh Plus computers may experience issues common to vintage electronics, such as:
* '''Capacitor aging''' leading to power supply instability or complete failure
* '''Overheating problems''' due to lack of internal cooling fan
* '''CRT display issues''' including loss of deflection or brightness degradation
* '''SCSI termination problems''' affecting external device connectivity
* '''Analog board component failure''' particularly in power regulation circuits

The lack of fan could cause the life of a Macintosh Plus to end early for some users. As the power supply would heat up, solder joints inside it would fracture, causing many problems, such as loss of deflection in the monitor or a complete loss of power.<ref>{{cite book |last=Pogue |first=David |title=Macworld Mac Secrets |publisher=IDG Books |year=1993 |isbn=1568840594}}</ref> Regular maintenance, including capacitor replacement and ensuring proper heat dissipation, can help preserve the functionality of these systems. For detailed procedures, refer to the [[Macintosh Plus General Maintenance]].

== PCB Schematics & Service Manual ==

The Macintosh Plus features two main PCBs: the '''Logic Board''' and '''Analog Board'''. Below are detailed schematics and the official Apple service manual for the Macintosh Plus.

=== Apple Service Manual ===
<pdf width="800" height="500">File:Macintosh Plus.pdf</pdf>

You can download the Service Manual here: [[File:Macintosh Plus.pdf|center|thumb|Apple Service Guide - Macintosh Plus]]

=== Logic Board & Analog Board Schematics ===

{| class="wikitable" style="width:50%; text-align:center;"
|+'''Macintosh Plus PCB Schematics'''
|-
! style="background-color:#f2f2f2; width:30%;"| Logic Board
! style="background-color:#f2f2f2; width:30%;"| Analog Board
|-
| [[File:MacintoshPlus_LogicBoard.jpg|thumb|center|250px|Macintosh Plus Logic Board]]  
[[File:MacintoshPlus_LogicBoard_Shematic.jpg|thumb|center|250px|Macintosh Plus Logic Board Schematic]]
| [[File:MacintoshPlus_AnalogBoard.jpg|thumb|center|250px|Analog Board]]  
[[File:MacintoshPlus_AnalogBoard_Schematic.jpg|thumb|center|250px|Analog Board Schematic]]
|}



== Capacitor Replacement Guide ==
Detailed capacitor replacement guidelines for both analog and logic boards can be found on the [[Macintosh Plus Capacitor Replacement Guide]] page.

== Retrobrite ==
To address plastic yellowing, detailed instructions can be found on the [[Retrobrite]] page.

== Troubleshooting ==
A comprehensive troubleshooting guide addressing no power, chime but no video, intermittent operation, Sad Mac errors, and floppy drive problems is available on the [[Macintosh Plus Troubleshooting|Macintosh Plus Troubleshooting]] page.

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

=== System Architecture at a Glance ===
{| class="wikitable styled-table" style="width:80%; text-align:center;"
! Sub-system !! Specification (Macintosh Plus, Jan 1986)
|-
| '''CPU''' || Motorola 68000 @ 7.8336 MHz  (15.667 MHz ÷ 2)<ref>{{cite web |url=http://www.easy68k.com/paulrsm/doc/dpbm68k1.htm |title=Design Philosophy Behind Motorola's MC68000 |author=Thomas W. Starnes |publisher=BYTE Magazine |date=April 1983 |access-date=2025-01-25}}</ref>
|-
| '''Bus width''' || 16-bit data • 24-bit address  (16 MB logical)  
|-
| '''ROM''' || '''128 KB "v4.0"''' Toolbox / HFS / SCSI Manager
|-
| '''RAM''' || 1 MB on four 256-K × 1 DRAM SIMMs — expands to '''4 MB''' via 30-pin SIMM slots  
|-
| '''Video''' || 512 × 342 monochrome frame-buffer (22.1 KB) DMA-shared with system RAM  
|-
| '''Sound''' || 8-bit PWM DAC via VIA timers • 22 kHz RC low-pass → LM380 amplifier  
|-
| '''Disks''' || Sony OA-D34V-22 800 KB auto-inject 3.5″ floppy  
|-
| '''I/O ports''' || DE-9 mouse/KB • DB-19 ext. floppy • '''DB-25 SCSI-1''' • RS-422 serial × 2 • 3.5 mm audio-out  
|}

=== Memory Map (Physical) ===
{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+'''Macintosh Plus Address Space'''
! Range !! Size !! Purpose
|-
| $000000 – $3FFFFF || 4 MB || '''DRAM''' (configured 1 MB – 4 MB)
|-
| $400000 – $41FFFF || 128 KB || '''ROM''' (v4.0 Toolbox)  
|-
| $480000 – $4BFFFF || 256 KB || '''I/O A''' – VIA 1, VIA 2, SCC, IWM, VBL PAL  
|-
| $580000 – $5BFFFF || 256 KB || '''I/O B''' – WD 5380 SCSI DMA registers  
|-
| $600000 – $FFFFFF || Mirrors / reserved
|}

''Frame-buffer note: still occupies the last 22 016 bytes of physical RAM (e.g. '''$3FE000 – $3FFFFF''' in a 4 MB system).''

== Technical Details ==

=== Processor Specifications ===
{| class="wikitable styled-table"
|-
! Component !! Specification
|-
| CPU || Motorola 68000 @ 8 MHz<ref>{{cite web |url=https://everymac.com/systems/apple/mac_classic/specs/mac_plus.html |title=Macintosh Plus (ED) Specs |publisher=EveryMac.com |date=1996 |access-date=2025-05-26}}</ref>
|-
| Data Bus || 16-bit<ref>{{cite web |url=https://lowendmac.com/2014/cpus-motorola-68000/ |title=CPUs: Motorola 68000 |publisher=Low End Mac |date=2014-06-14 |access-date=2025-05-26}}</ref>
|-
| Address Bus || 24-bit<ref>{{cite web |url=https://lowendmac.com/2014/cpus-motorola-68000/ |title=CPUs: Motorola 68000 |publisher=Low End Mac |date=2014-06-14 |access-date=2025-05-26}}</ref>
|-
| Internal Registers || 32-bit<ref>{{cite web |url=https://lowendmac.com/2014/cpus-motorola-68000/ |title=CPUs: Motorola 68000 |publisher=Low End Mac |date=2014-06-14 |access-date=2025-05-26}}</ref>
|-
| Performance || 0.7 MIPS<ref>{{cite web |url=https://lowendmac.com/1986/mac-plus/ |title=Mac Plus |publisher=Low End Mac |date=1986-01-16 |access-date=2025-05-26}}</ref>
|}

=== Memory Configuration ===
{| class="wikitable styled-table"
|-
! Type !! Specification
|-
| Standard RAM || 1 MB<ref>{{cite web |url=https://en.wikipedia.org/wiki/Macintosh_Plus |title=Macintosh Plus |publisher=Wikipedia |date=2025-04-28 |access-date=2025-05-26}}</ref>
|-
| Maximum RAM || 4 MB<ref>{{cite web |url=https://en.wikipedia.org/wiki/Macintosh_Plus |title=Macintosh Plus |publisher=Wikipedia |date=2025-04-28 |access-date=2025-05-26}}</ref>
|-
| SIMM Slots || 4 × 30-pin<ref>{{cite web |url=https://en.wikipedia.org/wiki/Macintosh_Plus |title=Macintosh Plus |publisher=Wikipedia |date=2025-04-28 |access-date=2025-05-26}}</ref>
|-
| SIMM Speed || 150ns<ref>{{cite web |url=https://lowendmac.com/1986/mac-plus/ |title=Mac Plus |publisher=Low End Mac |date=1986-01-16 |access-date=2025-05-26}}</ref>
|-
| ROM || 128 KB<ref>{{cite web |url=https://en.wikipedia.org/wiki/Macintosh_Plus |title=Macintosh Plus |publisher=Wikipedia |date=2025-04-28 |access-date=2025-05-26}}</ref>
|}

=== Physical Specifications ===
{| class="wikitable styled-table"
|-
! Dimension !! Measurement
|-
| Height || 13.6" (34.5 cm)<ref>{{cite web |url=https://www.dimensions.com/element/apple-macintosh-128k-1984 |title=Apple Macintosh 128K (1984) Dimensions |publisher=Dimensions.com |date=2024 |access-date=2025-05-26}}</ref>
|-
| Width || 9.6" (24.4 cm)<ref>{{cite web |url=https://www.dimensions.com/element/apple-macintosh-128k-1984 |title=Apple Macintosh 128K (1984) Dimensions |publisher=Dimensions.com |date=2024 |access-date=2025-05-26}}</ref>
|-
| Depth || 10.9" (27.7 cm)<ref>{{cite web |url=https://www.dimensions.com/element/apple-macintosh-128k-1984 |title=Apple Macintosh 128K (1984) Dimensions |publisher=Dimensions.com |date=2024 |access-date=2025-05-26}}</ref>
|-
| Weight || 16.5 lb (7.5 kg)<ref>{{cite web |url=https://lowendmac.com/1986/mac-plus/ |title=Mac Plus |publisher=Low End Mac |date=1986-01-16 |access-date=2025-05-26}}</ref>
|-
| Power Consumption || 60 watts maximum<ref>{{cite web |url=https://support.apple.com/kb/SP190 |title=Macintosh Plus: Technical Specifications |publisher=Apple Support |date=1986 |access-date=2025-05-26}}</ref>
|}

=== ROM Layout (128 KB, v4.0 "Plus-class") ===
{| class="wikitable styled-table" style="width:80%;"
! Offset !! Size !! Module
|-
| $400000 || 8 KB || 68000 vectors + Mini-Shell
|-
| $402000 || 20 KB || QuickDraw 1.2 (monochrome, relocatable)
|-
| $407000 || 52 KB || Toolbox, SANE, Font & Menu mgrs.
|-
| $414000 || 16 KB || Sony 800 KB floppy driver & IWM tables
|-
| $418000 || 24 KB || SCSI Manager, Disk Cache, HFS
|-
| $41E000 || 8 KB || I/O traps, Declarations, Copyright
|}

=== SCSI Sub-system ===
* Western Digital '''WD 5380''' NCR-compatible controller
* 5 MB s⁻¹ 8-bit synchronous (practically 1.2 MB s⁻¹ async)  
* DMA-like handshake handled in software by 68000 — no true DMA

=== Floppy-Disk Format (800 KB GCR) ===
* 80 tracks • double-sided variable-speed  
* 12 → 8 sectors/track (outer→inner) • 512-byte sectors  
* 800 KB formatted • still uses IWM (not yet SWIM)

=== Key I/O ICs ===
* '''6522 VIA × 2''' — timers, sound PWM, keyboard/mouse handshake<ref>{{cite web |url=http://www.easy68k.com/paulrsm/doc/dpbm68k2.htm |title=Design Philosophy Behind Motorola's MC68000 (Part 2) |author=Thomas W. Starnes |publisher=BYTE Magazine |date=May 1983 |access-date=2025-01-25}}</ref>
* '''8530 SCC''' — dual RS-422 serial (230 kbps)  
* '''IWM''' — Integrated Woz Machine floppy controller  
* '''WD 5380''' — 8-bit SCSI controller  
* '''MC6883 PAL''' — VBL interrupt & DRAM cycle arbiter

=== Sound Path ===
68000 → VIA Port A (8-bit sample) • VIA Timer 1 toggles Port B at 22.254 kHz → PWM  → RC filter  → LM380  → speaker / headphone jack.

=== RAM Upgrade Notes ===
* Uses four 30-pin SIMM sockets (Bank 0 & Bank 1).  
* Accepts 256 KB or 1 MB SIMMs, 150 ns or faster.  
* Mixed sizes allowed per bank (must match within a bank); 4 MB max.

=== Hardware Easter Egg ===
Boot while holding '''⌘ + Option + ⇧ + Clear''' to hear the hidden *bass-only* startup chime — final compact-Mac model to include it.<ref>{{cite book |last=Hertzfeld |first=Andy |title=Revolution in the Valley: The Insanely Great Story of How the Mac Was Made |publisher=O'Reilly Media |year=2005 |isbn=0596007191}}</ref>

== References ==
<references />

[[Category:Apple Vintage Computers]]

{{Navbox-AppleVintage}}