Editing Atari 1040STE (section)

== Memory and Storage ==
RAM organization and expansion
* Stock RAM: 1 MB ST‑RAM using 30‑pin SIMMs (some early boards used SIPPs). Configurations of 0.5/1/2/4 MB supported officially; 4 MB max via 4×1 MB or 2×2 MB depending on socketing; 2.5 MB is not officially supported.<ref>{{cite web|url=https://en.wikipedia.org/wiki/Atari_ST|title=Atari ST – STE memory (SIMM/SIPP)|publisher=Wikipedia|date=2025|access-date=2025-08-12}}</ref>
* Addressing: contiguous ST‑RAM in the lower 4 MB of the 24‑bit space; DMA sound fetches must reside in first 4 MB.<ref>{{cite web|url=https://bus-error.nokturnal.pl/atari_compendium/html/chap5.htm|title=Atari Compendium – DMA sound register map|publisher=Bus‑Error mirror|access-date=2025-08-12}}</ref>

ROM
* TOS 1.06 (1.60) or 1.62: 256 KB (two 128 KB ROMs in most STEs). 1.62 fixed desktop medium‑resolution boot bug in 1.60; users often upgrade to TOS 2.06 (256 KB) for enhanced desktop and 1.44 MB floppy support in Mega STE class machines.<ref>{{cite web|url=https://home.deds.nl/~dwvdburg/atari/tos.html|title=TOS versions overview|author=Dirk van den Burg|access-date=2025-08-12}}</ref><ref>{{cite web|url=https://en.wikipedia.org/wiki/Atari_TOS|title=Atari TOS|publisher=Wikipedia|date=2024|access-date=2025-08-12}}</ref>

Floppy and mass storage
* Floppy: 3.5″ DS/DD 720 KB internal; WD1772 controller (many -02‑02 variants). Stock STE units are DD; later HD support requires “AJAX” controller (C302096) not normally fitted to 1040STE (standard on Mega STE).<ref>{{cite web|url=https://temlib.org/AtariForumWiki/index.php/WD1772|title=WD1772|publisher=AtariForumWiki|access-date=2025-08-12}}</ref>
* ACSI hard‑disk: external via DB‑19; common modern replacements include UltraSatan/ACSI2STM. Early DMA IC C025913‑38 can cause write corruption on some STE boards; later C398739‑001 fixes timing (see Troubleshooting).<ref>{{cite web|url=https://www.chzsoft.de/site/hardware/new-atari-ste-bad-dma-investigation/|title=STE bad DMA investigation|author=Christian Zietz|date=2023-04-22|access-date=2025-08-12}}</ref>

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