		    Commonly Asked Questions of EISA-SC100	     11/16/92


 TRADEMARKS

    ASUSTeK and ASUS are registered trademarks of ASUSTeK Computer Inc.
    EISA-SC100 is a trademark of ASUSTeK Computer Inc.
    Adaptec and AHA-1542B are registered trademarks of Adaptec, Inc.
    ASPI is a trademark of Adaptec, Inc.
    Intel is a registered trademark of Intel Corporation.
    i386 and i486 are trademarks of Intel Corporation.
    Micro Channel, PS/2 and OS/2 are registered trademarks of IBM Corporation.
    Microsoft and MS-DOS are registered trademarks of Microsoft Corporation.
    Windows is a trademark of Microsoft Corporation.
    NCR is the name and mark of NCR Corporation.
    NetWare is a registered trademark of Novell, Inc.
    QEMM is a trademark of Quarterdeck Office Systems.
    Qualitas and 386MAX are registered trademarks of Qualitas, Inc.
    SCO is a registered trademark of The Santa Cruz Operation, Inc.
    ISC is a registered trademark of Interactive Systems Corporation.
    UNIX is a registered trademark of Bell Laboratories.



 Q: What are the major specification and features of EISA-SC100?

 A: EISA-SC100 is an EISA to SCSI host adapter.  The major specification and
    features as following:

    * 80C186-16MHz CPU as the Intelligent controller
    * Intel 82355 EISA BMIC (Bus Master Interface Controller) running at 33MHz
    * NCR 53C94 SCSI Controller
    * ASUSTeK SCSI-100X ASIC (Application Specific Integrated Circuit)
    * 64 KBytes local SRAM for 80186 CPU and FIFO (First-In First-Out) buffer
    * 32 KBytes local ROM for Code (MicroCode) storage
    * On-card BIOS for SCSI hard disks
    * Optional write back cache up to 16 MBytes
    * 32-bit EISA Bus Master Mode, transfer rate up to 33 MBytes/sec
    * Adaptec AHA-1542B compatible
    * Internal/External SCSI connectors support up to seven SCSI devices
    * Internal floppy interface supports up to two floppy disks
    * SCSI-2 command set
    * SCSI synchronous transfer rate up to 5 MBytes/sec
    * SCSI asynchronous transfer rate up to 5 MBytes/sec
    * Scatter/Gather
    * Mailbox structure for Multithreading



 Q: What is Bus Mastering?

 A: Bus Mastering is a method of data transfer that allows data to be moved
    between a peripheral controller and system memory without interaction with
    the host CPU.  This technique allows the peripheral controller to take
    control of the system bus, and in the case of EISA, to move data up to 33
    MBytes/sec.  Since the bus master transfers data without intervention of
    CPU or EISA DMA controller, someone considers it to be first-party DMA.



 Q: Is 80C186-16MHz fast enough for EISA bus?

 A: The role of 80C186 in EISA-SC100 is command/status processing and the data
    transfer is handled by 82355 BMIC to achieve EISA bus performance.	Since
    the data transfer cycles occupy over 99.99% of whole cycles, this
    well-designed 80C186 circuit will not slow down the overall speed.



 Q: Why cache on card?

 A: The EISA bus provides a great improvement of data transfer rate, but the
    disks (or other peripherals) are too slow and can not distinguish the
    difference between EISA bus and ISA bus.  On-card cache does not only
    support maximum bus transfer rate but also prevents slow mechanical
    movement when data is located in different areas of disk drive.  Second,
    the system CPU, no matter how fast, can do one thing at a time (even in
    multitasking mode).  The concurrent operation of on-card cache does not
    take any system overhead and provides best overall performance.



 Q: Why write back cache?

 A: Write back cache copies cached data to peripheral in background so the
    host system never waits for a write operation.  The write back cache may
    50 to 200 times faster than write through cache for a disk write.



 Q: What happened if power lost?

 A: Write back cache has risk to lose data if power lost.  To minimize this
    problem, EISA- SC100 does not use delay time for write back.  The actual
    write will automatically starts if there are no continuous read
    operations.  In the matter of fact, most multitasking operating systems
    such as UNIX and NetWare have cache in system memory also have risk to
    lose data if power lost.  For high degree data safety, UPS (Uninterrupted
    Power Supply) is recommended.



 Q: What is the advantage of hardware cache (on-card cache) than the software
    cache in the system memory?

 A: The software cache handled by OS and host CPU and requires a lot of system
    resources such as memory space and CPU time.  The hardware cache on card
    is handled by host adapter and running concurrently without penalty.
    Large software cache can degrade system performance for a variety of
    reasons.  However, completely disabling the caches of some operating
    systems also degrades performance.	The best situation is large hardware
    cache with small software cache.



 Q: What operating systems supported by EISA-SC100?

 A: Because EISA-SC100 is AHA-1542B compatible, the drivers support AHA-1542B
    will support SC100 too.  ASUSTeK also provides drivers for DOS and NetWare
    386 V3.11.	SCO UNIX, ISC UNIX and OS/2 2.0 shipped with embedded SCSI
    drivers and works with SC100.  For older versions of OS, such as DOS 2.x,
    NetWare 286, NetWare 3.10 (and earlier) and OS/2 1.x, are not supported.



 Q: What are the disk capacity limits with EISA-SC100?

 A: For DOS 5.0, the limit is 2 GBytes if "1GB+ Disk Support" of EISA-SC100 is
    enabled, and 1 GBytes if disabled.	Note that SC100 BIOS and Code support
    DOS disk partitions up to 7.84 GBytes, but DOS 5.0 can create disk
    partitions up to 2 GBytes.

    For SCO UNIX Release 3.2v2, the disk capacity may over 1 GBytes, but each
    file system has 1 GBytes limitation.  In Release 3.2v4, the disk capacity
    can exceed one GBytes, but the bootable file system is limited to 1
    GBytes.

    ISC UNIX (Interactive UNIX) v3.0 can handle disk over 1 GBytes, but v2.2.1
    supports disk up to 1 GBytes.

    If NetWare 386 V3.11 used with our NTSC100.DSK, the limit is 64 GBytes,
    but the bootable DOS partition is 1 GBytes maximum (note that NetWare 3.11
    server requires only a small DOS partition, e.g., only 10 MBytes).

    The HPFS (High Performance File System) of OS/2 2.0 can be used with disk
    over 1 GBytes but the bootable partition should less or equal 1 GBytes.
    If you are using the FAT partition of OS/2, the limit is 1 GBytes.

    Note:  ASUSTeK will revise above information if we have more news.



 Q: Since the EISA-SC100 is the 16-bit AHA-1542B compatible, does it mean that
    EISA- SC100 will get 16-bit performance for compatible operation?

 A: This is not a precisely talking.  The SC100 was designed with same I/O
    registers with AHA- 1542B, but uses enhanced command set and different
    data transfer method.  The SC100 uses Bus Master on 32-bit data bus to
    perform 33 MBytes/sec transfer rate, while the AHA- 1542B uses 16-bit data
    bus.  It is not problem for the different data transfer method, because
    any driver or software never cares the transfer method and the data
    transfer is handled by the SCSI host adapter itself.  In addition, the
    SC100 uses 32-bit address bus to support the system memory up to 4 GBytes.



 Q: Why the EISA-SC100 does not use DMA?

 A: DMA is a lower cost alternative to an intelligent bus master.  The EISA
    DMA functions are intended for I/O peripherals that do not require local
    intelligence peripheral interface.	The SC100 uses Bus Master to provide
    better performance and more functions.  By the way, the DMA channel
    emulation in EISA configuration is to keep software compatibility only.



 Q: The maximum SCSI transfer rate of EISA-SC100 is 5 MBytes/sec; is it the
    bottleneck?

 A: The 5 MBytes/sec is much faster than peripheral devices such as disk, tape
    and optical devices.  Actually, the bottleneck is the peripheral devices.
    This is another reason that EISA-SC100 implemented with cache.  From the
    system point of view, it deals with the 33 MBytes/sec EISA bus and caches
    on EISA-SC100 but not the SCSI bus.



 Q: What is Logical Unit Number (LUN)?

 A: Each SCSI device may contain up to eight sub-devices or Logical Units,
    assigned Logical Unit Numbers (LUN) 0-7.  Typically, each SCSI device will
    consist of a single peripheral unit such as a disk or tape drive, and will
    be accessed as LUN 0 by host adapter.  In addition to SCSI peripheral
    devices, the host adapter can interface to SCSI Bridge Controller devices.
    A Bridge Controller is a single SCSI device that can, in turn, control up
    to eight peripheral devices.  The eight peripheral devices are referred to
    by their LUN.  Since up to seven Bridge Controller devices can be
    connected to a single host adapter, a total of 56 peripherals could be
    controlled by a single EISA-SC100.



 Q: What is Scatter/Gather?

 A: When using virtual memory addressing schemes, system memory may appear
    contiguous to the user but is actually fragmented into many widely
    scattered physical address locations.  Because of this, it is often
    necessary when accessing a large amount of contiguous data from a
    peripheral device, to break up the transfer into many different locations
    in system memory.  Scatter/Gather is a method of providing multiple host
    addresses for data transfer in one command.  This greatly increases
    performance in environments such as UNIX, NetWare, OS/2 and Windows.



 Q: What is Mailbox structure?

 A: With today's application requirements, sophisticated operating systems,
    and performance capabilities of the latest systems using faster CPUs and
    higher bus transfer rates, it is desirable to have several different tasks
    running simultaneously in support of many different users.	These tasks
    require a wide variety of I/O peripheral devices such as hard disks, tape
    drives and optical devices.

    One advantage offered by SCSI bus is that up to 7 devices may be connected
    to the host adapter.  To manage the processing of each separate task being
    processed in a system without loading down the system CPU, it requires a
    method that takes advantage of the local intelligence features of the host
    adapter.

    One such method is the Mailbox structure of communication between the host
    system and host adapter.  Mailboxes are reserved storage areas that reside
    at a fixed contiguous memory location in the host system.  The mailboxes
    coordinate communications between the host system and the host adapter.

    Every task contains one outgoing mailbox for sending command information
    to host adapter, and one incoming mailbox for return status information to
    host system.  All mailboxes' information transfers are accomplished by the
    Bus Master operation of EISA- SC100.



 Q: What is the difference between Synchronous/Asynchronous transfers?

 A: Asynchronous, requires a handshake of REQ (request) and ACK (acknowledge)
    signals for every byte transferred, and synchronous, which allows a number
    (called offset here) of REQ signal pulses to be sent before first ACK.
    Synchronous negotiation is used to establish the REQ/ACK offset and
    minimum transfer period (in other words, maximum transfer rate).

    Basically, synchronous transfer is faster than asynchronous because the
    transfer period is reduced.  However, due to the increased overhead of
    negotiation, you may find the actual performance is better in asynchronous
    if the SCSI devices can't agree with smaller transfer period.  In other
    words, 5 MBytes/sec asynchronous is faster than 5 MBytes/sec synchronous.



 Q: What is the Synchronous Negotiation?

 A: Through the SCSI message protocol, the host adapter will automatically
    negotiate with each SCSI device for synchronous SCSI transfer and accept
    Message Reject from devices not supporting this feature.  If a device does
    not support synchronous data transfer, then the host adapter will utilize
    asynchronous data transfer mode for that device.  The EISA-SC100 will
    attempt a transfer rate of 5 MBytes/sec and an offset of 16.  If the
    device does not support those values, lesser values will be automatically
    negotiated by the host adapter without host software intervention.



 Q: What is the difference between Single-Ended/Differential SCSI?

 A: The SCSI bus supports two electrical specifications: Single-Ended and
    Differential.  The single-ended driver and receiver configuration uses TTL
    levels and allows cable lengths up to 6 meters, while the differential
    driver and receiver configuration uses EIA RS-485 signals to allow longer
    cable lengths up to 25 meters.

    Since differential is not commonly found on SCSI peripherals, the
    EISA-SC100 currently supports single-ended SCSI only.



 Q: What is Wide SCSI?

 A: Wide SCSI is an option that adds a second SCSI cable.  This cable provides
    a data path for 16 or 32-bit data.	This path has separate handshake
    signals and is for data transfer only.  The transfer rate is two or four
    times the present transfer rate of original SCSI.

    EISA-SC100 does not support wide SCSI.



 Q: What is Fast SCSI?

 A: Fast SCSI is an option that doubles the synchronous data transfer speed.
    This feature has tested only with differential drivers and receivers.  The
    speed is achieved by removing excess margins from certain times and
    delays.  To use the fast SCSI option, high quality cables are required.
    This option is compatible with normal synchronous SCSI.

    EISA-SC100 does not support fast SCSI.



 Q: What is the purpose of the on-card BIOS?

 A: The on-card BIOS of SC100 is used to install SCSI hard disks only, you may
    use this BIOS if you have one or two SCSI hard disks or you want boot the
    operating system from the SCSI hard disk.

    Note that there are limitations of the BIOS:

    * Can support up to two SCSI disks
    * The I/O base address of EISA-SC100 must be 330h
    * For one disk support, the SCSI disk's SCSI ID must be 0 (Target 0, LUN
      0).  For two disks support, the SCSI ID should be 0 (Target 0, LUN 0)
      and 1 (Target 1, LUN 0).



 Q: What is the purpose of ASUSDOSM.SYS?

 A: The ASUSDOSM.SYS DOS Manager is a DOS device driver used to support the
    Advanced SCSI Programming Interface (ASPI) under DOS environment.

    The major purpose of ASUSDOSM.SYS is interfacing to SCSI devices comply
    with ASPI protocol, such CD-ROM, tape drive, printer and plotter, etc.

    The ASUSDOSM.SYS also complies with the VDS and supports programs that use
    virtual memory, such as Microsoft Windows 3.0/3.1, Quarterdeck QEMM 386
    and Qualitas 386MAX.



 Q: What is VDS?

 A: VDS stands for Virtual DMA Service specification, it was introduced with
    the Micro Channel models of the PS/2 series to address problems inherent
    in protected mode use of DMA and Bus Mastering.  The DOS version of VDS
    uses software interrupt 4Bh, function 81h, subfunction 02h to 0Ch to
    implement this specification.  With this specification, the bus master
    devices can obtain the physical address of software that is running in the
    protected mode of i386 and i486.  It contains, among others, functions to
    allocate buffers at fixed physical addresses and to lock address ranges to
    prevent multiple DMA or bus mastering operations on the same memory.


 Q: What is the purpose of ASUSDISK.SYS?

 A: The ASUSDISK.SYS ASPI disk driver is a DOS device driver to support SCSI
    hard disks under DOS environment.  Because of ASPI protocol was used, the
    ASUSDOSM.SYS DOS Manager should be loaded before the ASUSDISK.SYS.

    You may need ASUSDISK.SYS if you want:

    * Install more than one EISA-SC100 host adapters
    * Install more than two hard disks
    * Set the SCSI ID of disks other than 0 or 1



 Q: What is the purpose of SCRAMBIO.SYS?

 A: The SCRAMBIO.SYS is a DOS device driver to move the SC100 BIOS to RAM for
    speed improvement.	For main board that does not support shadow RAM
    feature in the BIOS address space, this driver provides great improvement.
    For cached main board that provides shadow feature but without cacheable,
    this driver may provide slightly improvement.  It is unnecessary to use
    the SCRAMBIO.SYS if your main board provides both shadow and cacheable.



 Q: What is the purpose of ASUSFDSK.EXE?

 A: The ASUSFDSK.EXE is a utility used for SCSI disk partition under DOS
    environment.  For disks installed by on-card BIOS, you may use the DOS
    FDISK.EXE to do the disk partition.  For disks installed by ASUSDISK.SYS,
    you should use the ASUSFDSK.EXE to do disk partition.  Of course, you may
    use DOS FDISK.EXE to do partition for every disk with the SC100 set at I/O
    port 330h and disk SCSI ID 0 or 1, then reconnect the disks to SC100 that
    I/O port other than 330h or change the disk SCSI ID for further use.


 Q: What is the purpose of the NTSC100.DSK?

 A: The NTSC100.DSK is a disk device driver under NetWare 386 V3.11 and can
    support up to 64 GBytes disk capacity and multiple host adapters.

    The NTSC100.DSK also supports ASPI transport layer protocol.



 End of Q & A 
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