Editing Amiga Chip RAM (section)

== Chip RAM by model ==
Most stock Amiga systems were equipped with Chip RAM only and shipped with between 256&nbsp;[[binary prefix|kiB]] and 2&nbsp;MiB.

{| class="wikitable"
! Model
! Stock Chip RAM
! Maximum Chip RAM
! Width
|-
|[[Amiga 1000]]
|256&nbsp;KiB
|512&nbsp;KiB
|16-bit
|-
|[[Amiga 500]], [[Amiga 2000]], [[CDTV]]
|512&nbsp;KiB &ndash; 1&nbsp;MiB{{ref label|note_a|a|^}}
|512&nbsp;KiB &ndash; 1&nbsp;MiB{{ref label|note_b|b|^}}
|16-bit
|-
|[[Amiga 500 Plus]], [[Amiga 600]]
|1&nbsp;MiB
|2&nbsp;MiB
|16-bit
|-
|[[Amiga 3000]]
|1&nbsp;MiB
|2&nbsp;MiB
|32-bit{{ref label|note_c|c|^}}
|-
|[[Amiga 1200]], [[Amiga 4000]], [[Amiga CD32]]
|2&nbsp;MiB
|2&nbsp;MiB
|32-bit{{ref label|note_d|d|^}}
|}

The shared RAM [[data bus]] is 16-bit on [[Original Chip Set|OCS]] and [[Amiga Enhanced Chip Set|ECS]] systems{{ref label|note_c|c|^}}.  The later AGA systems use a 32-bit data bus controlled by the Alice coprocessor (replacing Agnus) and 32-bit RAM.  The memory clock runs at double the rate on AGA systems.  As a result, chipset RAM [[memory bandwidth|bandwidth]] is increased fourfold compared to the earlier 16-bit design.  However, 32-bit access is limited to CPU and graphics DMA and cannot be used for other devices.  The ECS-based A3000 also has 32-bit Chip RAM, but access is only 32-bit for CPU operations; the chipset remained 16-bit.

The maximum amount of Chip RAM is dependent on the Agnus/Alice version.  The original Agnus chip fitted to the A1000 and early A2000 systems is a 48-pin [[Dual in-line package|DIP]] package able to address 512&nbsp;KiB of Chip RAM.  Subsequent versions of the Agnus are in an 84-pin [[Chip_carrier#Plastic-leaded_chip_carrier|PLCC]] package (either socketed or [[surface-mount technology|surface-mounted]]).  All models except the A1000 are upgradable to 2&nbsp;MiB of Chip RAM.  The A500 and the early A2000B can accommodate 1&nbsp;MiB by installing a later revision Agnus chip (8732A) with minimal hardware modifications; late-production machines usually already contained that chip, so that only [[Jumper (computing)|jumper]] modifications were necessary.  Likewise, 2&nbsp;MB can be installed by fitting an 8372B Agnus and extra memory.

The maximum amount of Chip RAM in any model is 2&nbsp;MiB.  The Amiga 4000 [[motherboard]] includes a non-functional jumper that anticipated later chips and is labeled for 8&nbsp;MiB of Chip RAM&mdash;regardless of its position, the system only recognizes 2&nbsp;MiB due to the limitations of the Alice chip.<ref>{{cite web | url=http://www.zimmers.net/cbmpics/cbm/amiga/a4000jumpers.html | title=A4000 Motherboard Jumpers | accessdate=2 September 2011 | archive-url=https://web.archive.org/web/20191123044708/http://www.zimmers.net/cbmpics/cbm/amiga/a4000jumpers.html | archive-date=23 November 2019 | url-status=dead }}</ref>  However, the software emulator [[UAE (emulator)|UAE]] can emulate an Amiga system with the design limit of up to 8&nbsp;MiB of Chip RAM.<ref name="uae">{{cite web | title=Features of the UAE Amiga Emulator | url=http://amiga.technology/features | accessdate=4 January 2017 | archive-url=https://web.archive.org/web/20170105180734/http://amiga.technology/features | archive-date=2017-01-05 | url-status=dead }}</ref>