Glossary

A specific location in memory, designated either numerically or by a symbolic name.

One of the ways data is transferred over the SCSI bus. It is slower than synchronous data transfer.

A binary digit. The smallest unit of information a computer uses. The value of a bit (0 or 1) represents a two-way choice, such as on or off, true or false.

Provides, among other things, the reading and setting of SCSI parameters without the OS running.

A collection of wires in a cable or copper traces on a circuit board used to transmit data, status, and control signals. EISA, PCI, and SCSI are examples of buses.

A high-performance way to transfer data. The host bus adapter controls the transfer of data directly to and from system memory without bothering the computer’s microprocessor. This is the fastest way for multi-tasking operating systems to transfer data.

A unit of information consisting of eight bits.

The “brain” of the computer that performs the actual computations. The term Micro Processor Unit (MPU) is also used.

A topology in which every device is connected to two others, except for two-end devices that are connected to only one other.

An international committee on radio frequency interference.

Refers to the way a computer is set up; the combined hardware components (computer, monitor, key board, and peripheral devices) that make up a computer system; or the software settings that allow the hardware components to communicate with each other.

32-bit scheme (referred to as CRC-32) included in Ultra160 that ensures complete integrity of the transferred data. CRC is guaranteed to detect all single bit errors, any two bits in error, or any combination of errors within a single 32-bit range.

A program that allows a microprocessor (through the operating system) to direct the operation of a peripheral device.

A hardware configuration for connecting SCSI devices. It uses a pair of lines for each signal transfer (as opposed to single-ended SCSI, which references each SCSI signal to a common ground).

A method of moving data from a storage device directly to RAM, without using the CPU’s resources.

A feature that allows a peripheral to control the flow of data to and from system memory by blocks, as opposed to PIO (Programmed I/O), where the flow is byte by byte.

A software procedure in which a host system queries a device to determine the device’s ability to communicate at the data transfer rate that was negotiated.

A memory chip typically used to store configuration information. See Non-Volatile Random Access Memory (NVRAM).

A SCSI device installed outside the computer cabinet. External SCSI devices are connected in a chain using shielded cables.

A standard for SCSI data transfers. It allows a transfer rate of up to 10 MBytes/sec over an 8-bit SCSI bus, and up to 20 MBytes/sec over a 16-bit SCSI bus.

Federal Communications Commission.

Software that is permanently stored in ROM. In the case of PDC, it can be accessed during boot time without the aid of an operating or file system.

A rigid disk permanently sealed into a drive cartridge. A hard disk can store very large amounts of information.

The computer system in which a SCSI host bus adapter is installed. It uses the SCSI host bus adapter to transfer information to and from devices attached to the SCSI bus.

A circuit board and/or integrated circuit device that provides a SCSI bus connection to the computer system.

A SCSI device installed inside the computer cabinet. These devices are connected in a chain using an unshielded ribbon cable.

A path through which a device can get the immediate attention of the computer’s CPU. The PCI bus assigns an IRQ path for each SCSI host bus adapter.

A measure of computer storage equal to 1024 bytes.

A subdivision, either logical or physical, of a SCSI device. Most devices have only one logical unit, but up to sixteen are allowed for a 16-bit SCSI bus and eight for an 8-bit SCSI bus.

An encoded three-bit number for the logical unit.

A robust design methodology that improves power consumption, data integrity, cable lengths, and support for multiple devices while providing a migration path for increased I/O performance.

The part of a computer’s memory that is directly accessible by the CPU (usually synonymous with RAM).

A large circuit board that holds RAM, ROM, the microprocessor, custom integrated circuits, and other components that make a computer work. It also has expansion slots for host bus adapters and other plug-in boards.

A measure of computer storage equal to 1024 kilobytes.

See mainboard. In some countries, the term motherboard is not appropriate.

The initiation and control of more than one sequence of operations. This allows programs to operate in parallel.

The simultaneous accessing of data by more than one SCSI device. This increases the aggregate data throughput.

An EEPROM used to store configuration information.

A program that organizes the internal activities of the computer and its peripheral devices. An operating system performs basic tasks such as moving data to and from devices and managing information in memory. It also provides the user interface.

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 for data transfer rates less than 160 MB/s.

A local bus specification that allows connection of integrated peripheral controller components, peripheral add-in boards, and processor/memory systems.

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 bus adapter.

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 might not be.

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

See port address.

The system firmware on HP PA-RISC systems. It provides basic read/write capability. Usually kept as firmware (ROM based). The system firmware on the main board of a computer is used to boot and control the system.

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.

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

In general, 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.

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

The HBA’s SCSI chips contain a RISC processor, programmed through microcode scripts.

A host bus adapter and one or more SCSI peripherals connected by cables in a linear chain configuration. The host bus adapter can exist anywhere on the chain, allowing connection of both internal and external SCSI devices. A system can have more than one SCSI bus by using multiple host bus adapters.

Any device conforming to the SCSI standard that attaches to the SCSI bus by means of a SCSI cable. This includes SCSI host bus adapters and SCSI peripherals.

A unique identification for each SCSI device on the SCSI bus. Each SCSI bus has fifteen available SCSI IDs numbered 0 through 15 for Wide SCSI or 0-7 for 8-bit SCSI. The host bus adapter is usually assigned ID 7, which gives it priority to control the bus.

The SCSI specification that adds features to the original SCSI-1 standard.

The current SCSI specification, which adds features to the SCSI-2 standard.

A hardware specification for connecting SCSI devices. It references each SCSI signal to a common ground, as opposed to differential SCSI and low-voltage differential SCSI, which use a separate return for each signal.

A specification for a high-performance peripheral bus and command set. The original standard is now referred to as SCSI-1.

One of the ways data is transferred over the SCSI bus. Transfers are clocked with fixed-frequency pulses.

Controls the low level POST (Power On Self Test) and basic operation of the CPU and computer system.

The electrical connection required at each end of the SCSI bus, composed of a set of resistors.

A standard for SCSI data transfers. It allows a transfer rate of up to 20 MBytes/sec over an 8-bit SCSI bus, and up to 40 MBytes/sec over a 16-bit SCSI bus. The STA (SCSI Trade Association) supports using the term “Ultra SCSI” over the older term “Fast-20.”

(Also called Ultra3 SCSI) A standard for SCSI data transfers. It allows a data transfer rate of up to 160 MBytes/second over a 16-bit SCSI bus. The bus width is always 16 bits.

A standard for SCSI data transfers. It allows a transfer rate of up to 40 MBytes/sec over an 8-bit SCSI bus, and up to 80 MBytes/sec over a 16-bit SCSI bus. The STA (SCSI Trade Association) supports using the term “Ultra2 SCSI” over the older term “Fast-40.”

Voluntary Control Council for Interference.

Very High Density Cable Interconnect.

A SCSI-2 feature allowing 16-bit transfers on the SCSI bus. This doubles the transfer rate over the standard 8-bit SCSI bus.

The STA (SCSI Trade Association) term for SCSI bus width 16 bits, SCSI bus speed maximum data rate 40 MBytes/sec.

The STA (SCSI Trade Association) term for SCSI bus width 16 bits, SCSI bus speed maximum data rate 80 MBytes/sec.