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Released as the expansion bus of the Commodore Amiga 3000 in 1990, the Zorro III computer bus was used to attach peripheral devices to an Amiga motherboard. Designed by Commodore International lead engineer Dave Haynie, the 32-bit Zorro III replaced the 16-bit Zorro II bus used in the Amiga 2000. As with the Zorro II bus, Zorro III allowed for true Plug and Play autodetection (similar to, and prior to, the PC's PCI bus) wherein devices were dynamically allocated the resources they needed on boot.
Zorro III continued Zorro II's direct memory-mapped address design (unlike 80x86 processors, the MC68K family used in the Amiga did not have a separate I/O address mechanism). Just as with Zorro II on 24-bit systems, Zorro III reserved a large chunk of 32-bit real memory address space for large memory mapped cards, a smaller chunk with smaller allocation granularity for "I/O" type board. Zorro III was never supported on 24-bit address or 16-bit data devices—it required a full 32-bit CPU. The CPU could directly address any Zorro III device as memory, so Zorro memory expansions could be made (and were made) as well as it being possible to use video memory on a video card to be as system RAM.
As an asynchronous bus, Zorro III specified bus cycles of set lengths during which a transaction conforming to the specifications of the bus could be carried out. The initial implementation of Zorro III was in Commodore's "Fat" Buster (BUS conTrollER) gate array, assisted by a very high speed PAL and numerous TTL buffer chips for bus buffering, isolation, and multiplexing. The Amiga 4000 implementation was fundamentally the same, but integrated a second gate-array to replace the TTL buffers. The Buster chip provided bus arbitration, translation between the MC68030 bus protocols and either Zorro II or Zorro III bus cycles (geographically mapped based on the Zorro bus address), and a vectored interrupt mechanism, generally not used. Zorro II bus masters were legal bus hogs, but Zorro III devices were fairly arbitrated and had controller-limited bus tenure.
Despite being a 32-bit bus, Zorro III used the same 100 way slot and edge connector as Zorro II. The extra address and data lines were provided by multiplexing some of the existing connections with the nature of the lines changing at different stages of the bus access cycle (e.g. address becoming data). However, the bus was not fully multiplexed; the lower 8-bits of address were available during data cycles, which allowed Zorro III to support a fast burst cycle in page-mode. Properly designed Zorro II expansion cards could coexist with Zorro III cards; it was not a requirement of a Zorro III bus master to support DMA access to Zorro II bus targets. Cards could detect a Zorro III vs. Zorro II backplane, allowing certain Zorro III cards to function when connected to the older Zorro II bus, though at Zorro II's reduced data rates.
The Zorro III bus has a theoretical bandwidth of 150 MByte/s, based on an ideal Zorro III master and slave device running with minimum setup and hold times.[1][2][3] The real transfer speed between the Amiga 3000/4000 implementation of Zorro III and a Zorro III card is somewhere around 13.5 MByte/s due to the limitations of the Buster chip.[4] This was comparable to Intel's first PCI implementation, which peaked at 25 MByte/s. Zorro III was optimized for future single-chip implementations of the protocol, but the resources available at Commodore in 1990 limited the initial implementation.
This is also the limiting factor with 3rd party Amiga PCI expansion boards like e.g. Elbox Mediator PCI or the Matay Prometheus PCI (about 12 MByte/s PCI to 68k-system). DMA transfers between two Zorro III cards (or PCI cards on an PCI expansion board) can be much faster.[5]
^Dave Haynie, designer of the Zorro III bus, claims in this posting that the theoretical max of the Zorro III bus can be derived by the timing information given in chapter 5 of the Zorro III technical specification Archived 2012-07-16 at the Wayback Machine.
^Dave Haynie, designer of the Zorro III bus, claims in this posting that Zorro III is an asynchronous bus and with that does not have a classical MHz rating. A maximum theoretical MHz value may be derived by examining timing constraints detailed in the Zorro III technical specification Archived 2012-07-16 at the Wayback Machine, which should yield about 37.5 MHz. No existing implementation performs to this level.
^Dave Haynie, designer of the Zorro III bus, claims in this posting that Zorro III has a max burst rate of 150 MB/s.
^"amiga.org post by Michael Boehmer on real-life Zorro III speed". Archived from the original on 2012-02-29. Retrieved 2013-03-19.
expansion bus of the Commodore Amiga 3000 in 1990, the ZorroIII computer bus was used to attach peripheral devices to an Amiga motherboard. Designed by Commodore...
connector. Zorro II was succeeded by ZorroIII, a 32-bit, asynchronous bus. Amiga portal Amiga Hardware Database - Descriptions and photos of Zorro II cards...
The new 32-bit ZorroIII expansion slots provide for faster and more powerful expansion capabilities. In common with earlier Amigas the 3000 runs a 32-bit...
September 2011. Haynie, Dave (20 March 1991), The ZorroIII Bus Specification (PDF), Commodore-Amiga, Inc., archived from the original (PDF) on 16 July...
manufactured in yellow and green versions, contains two Amiga Video Slots, five 100-pin ZorroIII slots, and 4 ISA slots, and its case can accommodate up...
without requiring an expansion cage like the Amiga 1000 does. Not only does the Amiga 2000 include five Zorro II card slots, the motherboard also has four...
up through AmigaOS 3.9. It is the only Amiga-based system to support FireWire for video I/O. DraCo also offers an Amiga-compatible Zorro-II expansion...
expansion subsystem. The Amiga 3000 and 4000 lines use Super Buster for bus control and arbitration of both Zorro II and ZorroIII subsystems. Super Buster's...
Amiga 3000, but the motherboard has been heavily redesigned. As a result, the expansion-slot layout is more like the Amiga 2000's with five ZorroIII...
gate) on the Amiga 2000, which is the only motherboard hardware required by Autoconfig. Autoconfig is part of the Zorro II and ZorroIII expansion bus...
it to a "big-box" Amiga. These expansion kits allow use of PC/AT keyboards, hard-disk bays, CD-ROM drives, and Zorro II, ZorroIII, and PCI expansion...
detached keyboard system with expansion slots (two Zorro slots, video slot, CPU slot). A number of new Amiga models were announced after the end of the Commodore...
and speeds of Fast RAM. For example, an Amiga 3000 may contain 16-bit Zorro II expansion RAM, 32-bit ZorroIII expansion RAM, 32-bit motherboard RAM, and...
Zorro architecture did not spread to general computing use outside of the Amiga product line, but was eventually upgraded as Zorro II and ZorroIII for...
1987 DIN 41612 40 MByte/s NeXT, Macintosh II AmigaZorroIII 1990 2×50 2.54 mm card edge 150 MByte/s Amiga Multiplexed 32-bit. PDS 1990 DIN 41612 Macintosh...
numeric keypad, Zorro expansion slot, and other functionality, but added IDE, PCMCIA, and intended as a cost-reduced design. Designed as the Amiga 300, a non-expandable...
recorders, based on a SCSI system and a Zorro II Amiga expansion card. Expansion cards could transform an Amiga into a waveform monitor or vectorscope...
for Amiga computers built by DPS (Digital Processing Systems, Canada) in 1993. It fits into an Amiga'sZorro II/III slot available in the Amiga 2000/3000/4000...
IDE interface 4 ZorroIII slots A bus slot for the addition of accelerators and MPEG card Additional: MPEG level 1 supported PC or Amiga keyboard A scan...
driver API mainly used by third-party graphics hardware to interface with AmigaOS via a set of libraries. The software libraries may include software tools...
busboard full of expansion slots (much like S-100 busboards). It had five Zorro II Amiga compatible slots, and three DracoDirect slots. There was also a special...
Coleco ColecoVision Adam Commodore PET VIC-20 Commodore 16 Commodore 64 AmigaAmiga CD32 Google Android Stadia Microsoft MS-DOS MSX Windows 3.x Windows Windows...
and Canada, exclusively in French language. II^ Completed posthumously. III^ Release for Windows and PlayStation 2 was cancelled upon demise of Cryo...
Coleco ColecoVision Adam Commodore PET VIC-20 Commodore 16 Commodore 64 AmigaAmiga CD32 Google Android Stadia Microsoft MS-DOS MSX Windows 3.x Windows Windows...