ACSI, SCSI and IDE

ASCI

ACSI is an acronym for Atari Computer Systems Interface. This peripheral bus is very similiar to the industry standard SCSI (Small Computer Systems Interface) bus. This peripheral bus allows more than one device to be connected to the computer by way of standard signal lines.

The ACSI is an 8 bit bidirectional data bus that allows data to pass from a peripheral, such as your hard disk, to the host Atari ST computer. The transfer of data may also flow over the bus from the Atari ST to the peripheral. Data may be transfered at a maximum rate of 1.25 million bytes per second and may be transfered to or from any of eight possible control devices attached to the bus. These control devices are addressed as devices 0 to 7.

ACSI makes use of the DMA.

SCSI

SCSI makes use of the DMA.

DMA

DMA is an acronym for Direct Memory Access. When used in the context of a computer (such as the Atari ST) and its high performance peripherals (floppy and hard disks, laser printers, tape drives, CD ROMs, etc.). DMA refers to the direct transfer of data between the peripheral device and the computer's memory. This transfer is done without the direct intervention of the processor. The Atari ST provides an external DMA bus connection through the Atari Computer System Interface (ACSI) connector on the Atari ST computer.

Atari ST/TT/Falcon peripheral devices that use the DMA channel include

• the Atari floppy disk controller (which is connected directly to the DMA channel)
• internal & external SCSI of TT/MegaST/MegaSTE/Falcon
• external ACSI port of ST/STE/TT for the Laser printer through its APPC (Atari Page Printer Controller), the Hard Disk through its AHDI (Atari Hard Disk Interface), the CDAR Audio/ROM CD Unit, and the Removable Hard Disk.
• Sound system on STE, TT & Falcon
• other ?

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