Adaptec Glossary of Technical Terms --------------------------------------------------------------------------- Adaptec EZ-SCSI A user-friendly software program that automatically installs SCSI devices such as fixed disks and CD-ROM drives on a PC. Adaptec EZ-SCSI copies the required software programs to the PC's fixed disk and edits the configuration files so the host adapter can access the devices. ACK An acronym for Adaptec Cable Kit. AHA An acronym for Adaptec Host Adapter. AIC An acronym for Adaptec Integrated Circuit AIC-6260 Original version of the AIC-6360. AIC-6360 Second generation Adaptec single chip non-bus mastering ISA to SCSI host adapter (compatible with the first version, the AIC-6260). This chip is found on some Adaptec host adapters, such as the AVA-1505, AVA-1515, AHA-1520A, AHA-1522A, and the AMM-1570. Adaptec also licenses the chip to motherboard vendors and other I/O card manufacturers. AIC-7770 An Adaptec single chip RISC based bus mastering EISA to SCSI host adapter. This chip is found on some Adaptec host adapters, such as the AHA-2740A and the AHA-2840A series. Adaptec also licenses the chip to motherboard vendors and other I/O card manufacturers. AIC-7870 An Adaptec single chip RISC based bus mastering PCI to SCSI host adapter. This chip is found on some Adaptec host adapters, such as the AHA-2940 and the AHA-2940W. Adaptec also licenses the chip to motherboard vendors and other I/O card manufacturers. AMM An acronym for Adaptec Multimedia Machine APA An acronym for Adaptec Portable Adapter. ASPI Advanced SCSI programming Interface. A standard SCSI software interface that acts as a liaison between host adapters and SCSI device drivers. ASPI enables host adapters and device drivers to share a single SCSI hardware interface. ASPI MANAGER A software module that provides an interface between ASPI modules, a host adapter board, and the SCSI devices connected to the adapter. A single ASPI manager can handle multiple Input/Output requests from multiple ASPI modules. ASPI managers are put requests from multiple ASPI modules. ASPI managers are written for a specific operating system - such as DOS, OS/2 or Unix-and a specific family of host adapter boards. The Adaptec EZ-SCSI ASPI managers for DOS are ASPI4DOS, ASPIEDOS and ASPI2DOS. ASPI MODULE Device-level code specific to a particular kind of SCSI device that communicates with the ASPI manager. The Adaptec EZ-SCSI ASPI modules are ASPIDISK. ASPICD. ASW An acronym for Adaptec Software. ASYNCHRONOUS DATA TRANSFER A method of SCSI data transfer. This is the type of transfer rate originally introduced with SCSI 1. With this type of transfer method, transfer rates of 2 MBytes/sec are common. See also SYNCHRONOUS TRANSFER. AVA An acronym for Adaptec Value Adapter. --------------------------------------------------------------------------- BIOS An acronym for Basic Input/Output System. This is usually an EPROM with computer program instructions in it. A motherboard BIOS (usually by companies such as Phoenix, Award, and AMI) controls the basic functions of the computer (such as controlling the keyboard, monitor, etc.). With a SCSI host adapter, the BIOS is used to control SCSI hard disk drives and perform the boot function. If a host adapter does not have a BIOS, then hard disk drives controlled by that host adapter cannot be used to boot from (booting must be done from another source, such as floppy, IDE, or another SCSI host adapter with a BIOS). The BIOS must be enabled in order to function (e.g. a host adapter with a BIOS that is disabled acts the same as a host adapter without a BIOS). The BIOS can also contain useful software utilities, such as Adaptec's SCSISelect utility, which can be used to change the host adapter settings, format disks, and run simple SCSI diagnostics. For more information on SCSI host adapter BIOS, see the 'Troubleshooting Guide' in section 6 of this guide. BOOTING Booting is a process by which a computer starts and automatically loads the operating system. BUS A pathway for data in a computer system. All PCs have an expansion bus, which is designed to host add-on (expansion) devices, such as modems, adapter boards and video adapters. Expansion devices use the bus to send data to and receive data from the PC's CPU or memory. ISA, EISA and Micro Channel are the major bus standards used in PC's. BUS MASTERING A high performance method of data transfer in which the host adapter's on-board processor handles the transfer of data directly to and from a computer's memory without intervention from the computer's microprocessor. This is the fastest method of data transfer available for multitasking operating systems. Adaptec's AHA-1540, AHA-1640, and AHA-1740 series host adapters use bus mastering. (Also called Bus Master DMA or First Party DMA.) --------------------------------------------------------------------------- CACHING This is a process by which data requested by the operating system of a computer is retrieved from RAM instead of from a hard disk (or some other mass storage media). Caching algorithms will check if the requested data is in its 'cache' (or RAM). RAM access is an order of magnitude faster than today's mass storage devices, so the more accesses to the cache, the faster overall system performance will be. Cache can be on the host adapter, on the motherboard (controlled by the operating system), and on the SCSI device. Operating system vendors such as Novell and Microsoft recommend that cache not be used on the host adapter, since today's operating systems cannot work in conjunction with host adapters with on board RAM. This leads to a degradation in performance, and possible data loss. CACHING CD-ROM PAUSE AND PLAY "Pause and play" is caused by the slow access time of CD-ROM drives. The user experiences a delay while the application pauses as it loads information for playback. This is especially apparent when video or intensive graphics are combined with audio (see XA-Audio). CHICAGO In addition to being the Windy City in Illinois, this is also the code name for the next version of Microsoft's Windows (v4.0) and DOS (v7.0). This software is now commonly referred to as Windows '95. COMMAND SWAPPING A SCSI host adapter feature that allows up the host adapter to support up to 255 simultaneous commands. Without this feature, AIC-7770 based host adapters support up to four simultaneous commands. --------------------------------------------------------------------------- DEVICE DRIVER A software program that enables a PC to communicate with peripheral devices such as fixed disk drives and CD-ROM drives. Each kind of device requires a different driver. Device driver programs are stored on a PC's fixed disk and are loaded into memory at boot time. DIFFERENTIAL A term referring to the electrical characteristics of the signals used on the SCSI bus interface. Differential signals occupy two conductors with a positive (+) and negative (-) polarity component of the signal. This minimizes the effect of common mode signal noise and allow the SCSI bus to operate reliably over greater distances at a higher speed. (DMA) DIRECT MEMORY ACCESS A mechanism that allows hardware control of the transfer of streams of data to or from the main memory of a computing system. The mechanism may require setup by the host software. After initialization, it automatically sequences the required data transfer and provides the necessary address information. DOS PARTITION A section of a disk storage device, created by the DOS FDISK program, in which data and/or software programs are stored. Computers have a primary DOS partition that contains the special files needed to boot the computer. A computer's disk devices may also have extended DOS partitions. Each DOS partition is assigned a unique drive letter, such as C or D. A single disk device can have multiple partitions. After you have installed EZ- SCSI you can use the AFDISK utility program to partition disk devices. DOUBLE WORD PIO TRANSFERS This is a type of data transfer done by 386 and newer microprocessors. With the Adaptec AIC-6360 based host adapters (AHA-1510A/1520A/1522A), this can result in up to a 20% increase in performance over the AIC-6260 based host adapters. DSP Acronym for Digital Signal Processor. A Digital Signal Processor is a specialized computer circuit designed to perform speedy and complex operations on audio waveforms. Useful in processing audio and video signals. --------------------------------------------------------------------------- EEPROM An acronym for Electrically Erasable Programmable Read Only Memory. These devices can be erased instantly. EISA (Extended Industry Standard Architecture) A computer bus standard compatible with ISA; a 32-bit data path (bus). ENHANCED MODE The operation mode of the AHA - 1740A/1742A/1744 that takes full advantage of the EISA addressing range and register set. EMBEDDED With reference to operating system application and utility software, does not require additional diskettes. EPROM An acronym for Erasable Programmable Read Only Memory. These devices can be erased by placing them under an ultraviolet light for several minutes. They can then be reused. EZ-AUDIO Intelligent Windows based installation software for configuring audio functionality on the AMM-1570 and AMM-1510M. Adaptec EZ-Audio automatically modifies the appropriate configuration files under Windows and DOS. EZ-SCSI Adaptec software package for quick and easy installation. Also contains useful software utilities. --------------------------------------------------------------------------- FAST SCSI Provides for performance and compatibility enhancements to SCSI-1 by increasing the maximum synchronous data transfer rate on the SCSI bus from 5 MBytes/sec to 10 MBytes/sec. FULL SCSI A SCSI solution that includes BIOS and support software to provide boot capability for hard disk drives, support for drives larger than 1 B, and full compatibility with removable media products (hard drives, optical drives, tape drives, and Floptical drives). --------------------------------------------------------------------------- h This stands for hex, or hexadecimal. This is a counting system commonly used in computers. It is based on 16 instead of 10 (decimal). An 'h' after a number indicates that this is a hex number. HOST A microcomputer in which a host adapter is installed. The host uses software to request the services of the host adapter in transferring information to and from peripheral devices attached to the SCSI bus connector of the host adapter. HOST ADAPTER A printed circuit board that installs in a standard microcomputer and provides a SCSI bus connection so that SCSI devices can be connected to the microcomputer. --------------------------------------------------------------------------- IBM PC AT COMPATIBLE Any computer system that emulates exactly the IBM PC AT and that uses an ISA backplane bus. INDUSTRY STANDARD ARCHITECTURE The IBM PC AT functions have been duplicated by a number of manufacturers. All the IBM PC AT compatible machines use a backplane bus that very closely emulates the function of the backplane bus of the PC AT. Because of the broad usage of this bus structure, it has become known as the Industry Standard Architecture bus, even though there is no presently accepted standard for the bus. INTERRUPT 13 This is the software interrupt for disk I/O used by DOS. DOS does 'Interrupt 13 calls' to read or write from a diskettes. A SCSI host adapter translates these Interrupt 13 commands into SCSI commands for SCSI disk drives. INTERRUPT 19 This is the software interrupt that handles the boot function. The boot code is typically handled by the motherboard BIOS, but can optionally be handled by the host adapter BIOS with some Adaptec host adapters. I/O Refers to an operations, program, or device whose purpose is to enter data into or to extract data from a computer. I/Oware In addition to hardware and software, I/O is the third critical component for today's PC system performance. Adaptec I/Oware products speed the flow of data from one part of a system to another, significantly improving overall performance. IRQ Interrupt Request Channel. The IRQ of a host adapter can be changed to several different settings by changing jumpers and/or switch settings on the adapter board. ISA Industry Standard Architecture expansion bus. A type of computer bus used in most PC's. ISA enables expansion devices like network cards, video adapters and modems to send data to and receive data from the PC's CPU and memory 16 bits at a time. Expansion devices are plugged into sockets in the PC's motherboard. ISA is sometimes called the AT Bus, because it was originally introduced with the IBM PC-AT in 1983. --------------------------------------------------------------------------- MCA (Micro Channel Architecture) IBM PS/2 (models 50-95) and compatible computers have a MCA computer bus inside. Can be driven by multiple independent bus master processors. MULTIMEDIA PC (MPC) A computer configured to easily store and retrieve large multimedia files. Typically, this configuration will include a high capacity, high performance SCSI-2 hard drive, removable media, and advanced audio. The AMM-1570 and AMM-1510 Multitasking The execution of commands in such a way that more than one command is in progress at the same time. MULTITHREADING A situation in which a host adapter has more than one outstanding command to two or more SCSI devices. --------------------------------------------------------------------------- Narrow SCSI device (as opposed to Wide SCSI device) This is the term attributed to today's 8 bit standard SCSI devices. This term is necessary to distinguish today's 8-bit SCSI devices to 16-bit Wide SCSI devices. --------------------------------------------------------------------------- PERIPHERAL A SCSI device installed on a computer system. PIO (Programmed Input/Output) A method of data transfer in which the host microprocessor transfers data to and from memory via the computer's I/O ports. PIO enables very fast data transfer rates, especially in single-tasking operating systems like DOS. PLUG AND PLAY (or PLUG & PLAY) A standard, pioneered by Microsoft and endorsed by industry leaders. This standard hopes to address the problems of adding I/O adapters to a PC computer system. Adapters designed to the Plug and Play standard will self configure, and automatically resolve system resources such as interrupts (IRQ), DMA, port addresses, and BIOS addresses. PORT I/O ADDRESS A window through which software programs communicate commands to an installed host adapter board. The commands are communicated 8 bits at a time. PROGRAMMED INPUT/OUTPUT A method of data transfer in which the host microprocessor transfers data to and from memory via the computer's I/O ports. PIO enables very fast data transfer rates, especially in single-tasking operating systems like DOS. The Adaptec AHA-1510 and AHA-1520 host adapters and the AIC-6260 SCSI protocol controller use this data transfer method. PROM An acronym for Programmable Read Only Memory. This is a version of a ROM that is programmable. --------------------------------------------------------------------------- REMOVABILITY A feature where the media in a removable media disk drive can be removed, then replaced with the same or different media without causing problems to the operating system. If removability was not supported, media in a removable media drive could not be removed without potential loss for data unless the computer was turned off. RISC A specialized processor that has been designed to handle a smaller set of instructions for increased performance. ROM An acronym for Read Only Memory. This is generally a chip on a computer or I/O card with software programmed inside of it that controls some function or functions. --------------------------------------------------------------------------- SCAM (SCSI Configures Auto Magically) This is also known as Plug and Play for SCSI. Using this specification, the SCSI host adapter is able to automatically select the SCSI ID of itself and attached SCSI devices. It can also enable/disable termination as required to properly terminate the SCSI bus. This is an attempt to make SCSI easier to use, since the user no longer has to worry about setting SCSI ID jumpers or SCSI bus termination. SCSI (Small Computer Systems Interface) A PC bus interface standard that defines standard physical and electrical connections for devices. SCSI provides a standard interface that enables many different kinds of devices, such as disk drives, magneto optical disks, CD-ROM drives, and tape drives to interface with the host computer. SCSI DEVICE A device such as a host adapter board, fixed disk drive or CD-ROM drive that conforms to the SCSI interface standard and is attached to a SCSI bus cable. The device may be an initiator, a target, or capable of both types of operation. SCSI OVERHEAD This is the time it takes for the host adapter to internally process a SCSI command. Adaptec RISC based host adapters have the advantage of extremely low SCSI overhead, which greatly increases overall system performance. STANDARD MODE The operation mode of the AHA-1740A/1742A/1744 that allows software drivers written for the AHA-1540/1542/1640 family to operate fully on the board. This has no performance limitations but does not allow addressing beyond 16 MBytes in the DOS environment. SYNCHRONOUS TRANSFER A method of SCSI data transfer. With this type of data transfer, the SCSI host adapter and the SCSI device agree to a transfer rate that both support (this is known as synchronous negotiation). With this type of data transfer method, transfer rates of 5 MBytes/sec or 10 MBytes/sec (for FAST SCSI) are common. --------------------------------------------------------------------------- TAGGED QUEUING A SCSI-2 feature that increases performance on SCSI disk drives. With tagged queuing, the host adapter, the host adapter driver, and the hard disk drive work together to increase performance by reordering the requests from the host adapter to minimize head switching and seeking. For example, the host adapter may ask for the following data in the following order; LBA 0, 1, 101, 102, 5, 6 (LBA = logical block address, or a byte of data) Without tagged queuing: If tagged queuing was not enabled, the drive would seek to LBA 0, transfer bytes 0, then 1, then seek to 101, transfer 101 and 102, then seek back to lba 5, transfer 5, then 6. ===>involves 3 seeks (initial seek to 5, seek to 101, then seek back to 5) With tagged queuing: If tagged queuing was enabled, the drive would seek to LBA 0, transfer bytes 0, then 1, 5 and 6, then seek to 101, transferring 101 and 102. At this point all the data would be transferred. ===>involves 2 seeks (initial seek to 5, then the seek to 101) Seeking on a disk drive takes a relatively long time, so having seeks and head switches really speeds up performance. TERMINATION A physical requirement of the SCSI bus. The first and last devices on the SCSI bus must have terminating resistors installed, and the devices in the middle of the bus must have terminating resistors removed. --------------------------------------------------------------------------- VESA (Video Electronics Standards Association) This association is responsible for setting standards in all areas of graphics and video technology. VDS (Virtual DMA Services) This is a software standard developed by Microsoft so that bus master host adapters could work efficiently under DOS protected mode and virtual 86 mode programs. Such programs that use the protected mode of the processor include MS Windows, Quarterdeck QEMM and Qualitas 386MAX. The VDS support is either provided in the DOS device driver (such as in ASPI4DOS.SYS) or by the host adapter BIOS (such as the AHA-1540CF/1542CF host adapters). VL-Bus A specification for a local bus developed by the VESA local bus committee. --------------------------------------------------------------------------- Wide SCSI Provides for performance and compatibility enhancements to SCSI-1 by adding a 16- or 32- bit data path. Combined with Fast SCSI, this can result of SCSI bus data transfer rates of 20 MBytes/sec (with a 16-bit bus) or 40 MBytes/sec (with a 32-bit bus).