Editing Macintosh 128K (section)

== 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 128K, Jan 1984)
|-
| '''CPU''' || Motorola 68000 @ 7.8336 MHz (15.667 MHz ÷ 2){{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}}
|-
| '''Bus width''' || '''16-bit data''' • 24-bit address (16 MB logical space)
|-
| '''ROM''' || '''64 KB "Boot/Toolbox"''' — 4 × TMS2532 16 KB mask ROMs{{cite web |url=https://support.apple.com/kb/SP186?locale=en_US |title=Macintosh 128K: Technical Specifications |publisher=Apple Support |access-date=2025-01-25}}
|-
| '''RAM''' || '''128 KB DRAM''' (64 × MT4264-15, 150 ns) — '''non-expandable'''{{cite web |url=https://americanhistory.si.edu/collections/object/nmah_334371 |title=Apple Macintosh Microcomputer |publisher=National Museum of American History |access-date=2025-01-25}}
|-
| '''Video''' || 512 × 342 mono — '''22.1 KB frame buffer''' shared with system RAM<br>Display DMA @ 15.667 MHz steals ~60% of CPU cycles during active scan
|-
| '''Sound''' || 8-bit DAC via VIA Port A • 22.254 kHz PWM → RC filter → speaker
|-
| '''Storage''' || Sony OA-D34V 400 KB GCR 3.5″ drive • IWM controller<br>Variable speed: 394 RPM (outer) → 590 RPM (inner tracks)
|-
| '''Ports''' || DE-9 mouse • DE-9 keyboard • DB-19 ext. floppy • RS-422 serial × 2 • 3.5mm audio
|-
| '''Expansion''' || '''None''' — no slots, non-upgradeable RAM
|}

=== Memory Map (Physical) ===
{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+'''Macintosh 128K Address Space'''
! Range !! Size !! Purpose
|-
| $000000 – $01FFFF || 128 KB || '''DRAM''' (actual system memory)
|-
| $020000 – $03FFFF || 128 KB || '''DRAM mirrors''' (unused on 128K)
|-
| $400000 – $40FFFF || 64 KB || '''ROM''' (Boot/Toolbox)
|-
| $410000 – $41FFFF || 64 KB || '''ROM mirrors'''
|-
| $600000 – $6007FF || 2 KB || '''VIA 1''' (system timers, sound)
|-
| $800000 – $8007FF || 2 KB || '''VIA 2''' (keyboard, mouse, floppy)
|-
| $A00000 – $A007FF || 2 KB || '''SCC''' (serial communications)
|-
| $C00000 – $C007FF || 2 KB || '''IWM''' (floppy disk controller)
|-
| $E00000 – $EFFFFF || 1 MB || '''Slot space''' (unused on 128K)
|}

*Frame-buffer:* 22,016-byte display buffer at '''$12700 – $1FFFF''' (top of RAM); DMA fetches pixels during active scan, reducing CPU performance by ~40%.

=== ROM Layout (64 KB) ===
{| class="wikitable styled-table" style="width:90%;"
! Offset !! Size !! Module
|-
| $400000 || 4 KB || 68000 exception vectors + Boot code
|-
| $401000 || 16 KB || QuickDraw 1.0 (monochrome bitmap routines)
|-
| $405000 || 24 KB || Macintosh Toolbox (Window/Menu/Dialog Managers)
|-
| $40B000 || 8 KB || SANE (Standard Apple Numeric Environment)
|-
| $40D000 || 6 KB || Sony IWM floppy driver
|-
| $40E800 || 6 KB || System utilities & resource manager
|}

=== Video Timing ===
{| class="wikitable styled-table" style="width:70%; text-align:center;"
! Parameter !! Value
|-
| Pixel clock || 15.667 MHz ÷ 2 = 7.833 MHz
|-
| Horizontal total || 704 pixels (512 active)
|-
| Vertical total || 370 lines (342 active)
|-
| Refresh rate || 60.15 Hz
|-
| Memory bandwidth || ~22 MB/s (shared with CPU)
|}

=== Floppy Disk Format (400 KB Sony GCR) ===
* '''80 tracks''' • single-sided • variable-speed GCR encoding
* '''12 sectors/track''' (outer) decreasing to '''8 sectors/track''' (inner)
* '''Sector size:''' 512 bytes • Total capacity: 409,600 bytes
* '''IWM controller''' with software-controlled stepper motor timing

=== Key I/O ICs ===
* '''6522 VIA × 2''' (MOS Technology) — system timers, sound PWM, I/O 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''' (Zilog) — dual RS-422 serial ports (230.4 kbps max)
* '''IWM''' (Apple custom) — Integrated Wozniak Machine floppy controller
* '''MC6883 PAL''' (Motorola) — address decode, 60 Hz VBL interrupt generation

=== Sound System ===
68000 writes 8-bit samples to VIA Port A at 22.254 kHz. VIA Timer 1 toggles Port B to create PWM signal, which passes through RC filter (R=10kΩ, C=0.1µF) to internal 8-ohm speaker or rear 3.5mm audio jack.

=== Memory Limitations & Performance Impact ===
The 128K's memory constraint created several operational challenges:
* '''Application switching''' required complete disk swaps due to insufficient RAM
* '''MultiFinder''' (cooperative multitasking) was impossible until 512K model
* '''Virtual memory''' concepts were unused due to single-floppy, no-HDD configuration
* '''System overhead''' consumed ~20KB, leaving only ~100KB for applications and documents

=== Hardware/Easter Facts ===
* First consumer computer to ship with 3.5" Sony floppy drives (later industry standard){{cite book |last=Levy |first=Steven |title=Insanely Great: The Life and Times of Macintosh, the Computer that Changed Everything |publisher=Penguin Books |year=1994 |isbn=0140291773}}
* Hidden startup chime: Hold '''⌘ + Option + Shift + Delete''' during boot for deep bass tone{{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}}
* Logic board manufactured by Apple in Fremont, California facility{{cite web |url=https://www.computerhistory.org/timeline/1984/ |title=1984 Timeline of Computer History |publisher=Computer History Museum |access-date=2025-01-25}}
* Case design influenced by Braun radio aesthetics via Hartmut Esslinger
* '''"Twiggy Mac"''' prototype used dual 5.25" drives before Sony partnership{{cite web |url=https://archive.org/details/OriginalMacBrochure1984 |title=Original Apple Macintosh 128K Brochure 1984 |publisher=Apple Computer |year=1984 |access-date=2025-01-25}}
* Custom Motorola 68000 processors marked "SC87839L" used in development prototypes{{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}}