ABIT COMPUTER CORPORATION

AT420/AT425/AT433/AT450

Processor         80486SX/80486DX
Processor Speed   20/25/33/50MHz
Chip Set          SIS
Max. Onboard DRAM 32MB
Cache             32/64/128/256/512/1024KB
BIOS              AMI
Dimensions        330mm x 218mm
I/O Options       None
NPU Options       4167

[Image]

                                CONNECTIONS

  Purpose                   Location    Purpose                  Location

  Speaker                     CN1       Turbo switch               JP1

  Power LED & keylock         CN2       Turbo LED                  JP2

  External battery            CN3       Reset switch               SW1

                        USER CONFIGURABLE SETTINGS

                Function                     Jumper          Position

  »   CMOS memory normal operation             JP5           pins 1 & 2
                                                              closed

      CMOS memory clear                        JP5           pins 2 & 3
                                                              closed

  »   Monitor type select monochrome           JP7             Open

      Monitor type select color                JP7            Closed

  »   Factory configured - do not alter        JP8             Open

  Note:Jumper JPX3 is closed using an 8-pin terminating resistor.

              DRAM CONFIGURATION

      Size          Bank 0          Bank 1

      1MB         (4) 256K x 9       NONE

      2MB         (4) 256K x 9   (4) 256K x 9

      4MB         (4) 1M x 9         NONE

      8MB         (4) 1M x 9      (4) 1M x 9

      16MB        (4) 4M x 9         NONE

      32MB        (4) 4M x 9      (4) 4M x 9

                            CACHE CONFIGURATION

      Size          Bank 0        Bank 1          TAG         Location

      32KB        (4) 8K x 8       NONE       (1) 8K x 8         T-1

      32KB        (4) 8K x 8    (4) 8K x 8    (2) 16K x 4        T-2

      64KB        (4) 8K x 8    (4) 8K x 8    (1) 8K x 8         T-1

      64KB        (4) 8K x 8    (4) 8K x 8    (2) 16K x 4        T-2

     128KB        (4) 32K x 8      NONE       (1) 8K x 8         T-1

     128KB        (4) 32K x 8      NONE       (2) 16K x 4        T-2

     256KB        (4) 32K x 8   (4) 32K x 8   (2) 16K x 4        T-2

     512KB        (4) 128K x       NONE       (1) 32K x 8        T-1
                      8

     512KB        (4) 128K x       NONE       (2) 64K x 4        T-2
                      8

     1024KB       (4) 128K x    (4) 128K x     (1) 128K x        T-1
                      8             8              8

     1024KB       (4) 128K x    (4) 128K x    (2) 64K x 4        T-2
                      8             8

                        CACHE JUMPER CONFIGURATION

     Size           JP3           JP4            JPX4           JPX5

     32KB          Open           Open        pins 1 - 8      pins 1 - 8
                                                closed         closed

     64KB          Open           Open        pins 9 - 16    pins 3 - 10
                                                closed         closed

    128KB          Open          Closed       pins 1 - 8     pins 5 - 12
                                                closed         closed

    256KB          Open          Closed       pins 9 - 16    pins 7 - 14
                                                closed         closed

    512KB          Open          Closed       pins 1 - 8     pins 9 - 16
                                                closed         closed

    1024KB        Closed         Closed       pins 9 - 16    pins 9 - 16
                                                closed         closed

  Note:Jumpers JPX4 & JPX5 are closed using 8-pin terminating resistors.

   CACHE JUMPER CONFIGURATION

   Type       JP6       JPX3

  80486SX    Closed     Open

  80486DX     Open     Closed