A500 Plus

Just after the A2000 Commodore released its first affordable machine, the A500. It is basically an A2000 in a compact case with limited expansion capabilities, aimed at the low-end users.
The A500 Plus is the same machine with more memory, more screen modes and upgraded Kickstart.


68000 @ 7-28 MHz
68020 @ 7-33 MHz
68030 @ 16-50 MHz
68040 @ 28-35 MHz

All A500 models has a socketed 68000 @ 7.14 MHz on their motherboard. Upgrading the processor requires the use of an accelerator board attached either to the 68000 socket or the side expansion connector.


up to 2 MB Chip RAM
up to 32 MB Fast RAM on processor boards
up to 8 MB Fast RAM on side expansion cards

The A500 shipped with 512 kB Chip RAM which can be upgraded to 1 MB, while the A500 Plus has 1 MB Chip RAM soldered to its motherboard which can be expanded to 2 MB.
24 bit Fast RAM can be added using trapdoor or side expansion cards up to 8 MB, and 32 bit Fast RAM using processor boards featuring a 68020 or better.

Custom chips

Fat Agnus - OCS / ECS display controller
Denise / Super Denise - OCS / ECS display encoder
Paula - audio and I/O controller
Gary - system address decoder

The A500 (OCS chip set) and A500 Plus (ECS chip set) support the following screen modes:

PAL, non-interlaced
PAL, interlaced
NTSC, non-interlaced
NTSC, interlaced
50 Hz, 15.60 kHz
50 Hz, 15.60 kHz
60 Hz, 15.72 kHz
60 Hz, 15.72 kHz
320×200 - 1280×400
73 Hz, 15.76 kHz
15 Hz, 15.72 kHz
640×480 - 640×960
640×400 - 640×800
400×300 - 800×600
60 Hz, 31.44 kHz
70 Hz, 31.43 kHz
72 Hz, 24.62 kHz

A500s using the OCS chip set support either PAL or NTSC screen modes, not both.
Low resolution screen modes offer up to 32 colours from a palette of 4096, 64 in EHB mode or 4096 in HAM mode. High resolution screen modes offer 16 colours from 4096, super-high resolution and productivity modes offer 4 colours from a palette of 64.
4 channel stereo 8 bit audio output with frequencies up to 28 kHz when using screen modes with 15 kHz, or up to 56 kHz when using screen modes with higher horizontal frequency.
A500s with the OCS chip set shipped with Kickstart 1.2 first, later with 1.3. The A500 Plus shipped with 2.04 Kickstart ROM. All versions can be replaced with a 3.1 one.

Expansion slots

1× trapdoor expansion slot
1× side expansion connector

The trapdoor slot on the A500 is designed for memory expansion cards. The A500 supports 512 kB and the A500 Plus supports 1 MB RAM via this slot.
The 86 pin side expansion connector can be used for Fast RAM expansions, hard disk controllers and even for processor boards.

The A500 has a vast array of upgrade options, including processor cards, SCSI or IDE controllers and many other types of expansion.


1× serial DB25 male, RS232
1× parallel DB25 female, Centronics
1× video DB23 male, analog RGB
1× composite, black & white
2× mouse/game DB9 male
2× stereo audio RCA jack
1× external floppy DB23 female
1× internal floppy 34 pin header

The floppy drive controller supports up to four devices - one attached to the internal floppy header and three connected to the external floppy port. Both double and high density disk drives are supported.
A 880 kB double density floppy disk drive is built into the A500's compact case.

Motherboard revisions

revision 3 (Photo)
512 kB Chip RAM on motherboard as 16 chips
Kickstart 1.2 ROM
revision 5 (Photo)
Fat Agnus 8370 (NTSC) or 8371 (PAL)
revision 6 (Photo)
Fat Agnus 8372A (part of the ECS chip set) supports 1 MB Chip RAM
Agnus is rotated 90° counter clockwise
512 kB Chip RAM on motherboard as 4 chips
empty places for other 4 chips giving 1 MB RAM on the motherboard
Kickstart 1.3 ROM
revision 7
revision 8 (Photo)
Kickstart 2.04 ROMs and ECS chip set: Fat Agnus (8375), Super Denise (8373)
512 kB Chip RAM on the motherboard
battery and clock circuit is missing
A500 Plus:
1 MB Chip RAM on the motherboard
battery backed up real time clock