parity checking A way to verify the accuracy of data transmitted over the SCSI bus. One bit in the transfer is used to make the sum of all the 1 bits either odd or even (for odd or even parity). If the sum is not correct, an error message appears. SCSI uses odd parity.

PCI (peripheral component interconnect) A local bus specification that allows connection of integrated peripheral controller components, peripheral add-in boards, and processor/memory systems. It bypasses the slower ISA and EISA busses.

peripheral devices A hardware device (such as a video monitor, disk drive, printer, or CD-ROM) used with a computer and under the computer’s control. SCSI peripherals are controlled through a SCSI host adapter.

pin-1 orientation The alignment of pin 1 on a SCSI cable connector and the pin 1 position on the SCSI connector into which it is inserted. External SCSI cables are keyed to ensure proper alignment, but internal SCSI ribbon cables may not be.

PIO (programmed input/output) A way the CPU can transfer data to and from memory via the computer’s I/O ports. PIO can be faster than DMA, but requires CPU time.

port address Also Port Number. The address through which commands are sent to a host adapter board. This address is assigned by the PCI bus.

port number See port address.

queue tags A way to keep track of multiple commands while allowing increased throughput on the SCSI bus.

RAM (Random Access

Memory) Generally, the computer’s primary working memory in which program instructions and data are stored and are accessible to the CPU. Information can be written to and read from RAM. The contents of RAM are lost when the computer is turned off.

RISC core Symbios SCSI chips contain a RISC (Reduced Instruction Set Computer) processor, programmed through microcode scripts.

ROM (Read-Only Memory)

Memory from which information can be read but not changed. The contents of ROM are not erased when the computer is turned off.

SCAM (SCSI Configured AutoMatically) A method to automatically allocate SCSI IDs via software when SCAM compliant SCSI devices are attached.

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