AST HotShot/286
        Introduced: 1987 
          Interface: 8-bit ISA
           
          Cost When New: $645 (Nov 1987)
           
          Part Number: 202160 
          Board Revisions: 202160-001, 202160-002
         
        The HotShot/286 was a CPU upgrade board for the IBM PC or PC/XT computer. It contained an Intel 80286-10 CPU and cache memory. It also provided a socket for an 80287 math coprocessor. 
        The expansion card came with a ribbon cable which connected it to a small CPU daughtercard that plugged into the motherboard's CPU socket after you removed the original CPU from the motherboard and put it on this daughtercard instead. 
        A set of 8 DIP switches on the card's backplate could be used to define the areas of the 1 MB address space to be cached. A jumper, JP1, was used to set the default boot-up mode of the card (either 80286 mode or 8088/8086 mode). 
        Actual performance improvements were limited to the 80286 CPU being able to process instructions faster/more efficiently than the original CPU, though given that it was on an 8-bit expansion card, communication with the motherboard was still limited to the slower 8-bit speed. This is where the card's onboard cache came into play. By caching  the memory, the card was able to counter what would otherwise seriously limit the performance gains of the card.         
        The card came with a drivers & utilities disk that included HOTSHOT.EXE to switch between the 8088 and 80286 CPU. One of the main reasons for this capability to switch between the original CPU and the HotShot/286's onboard 80286 CPU without the need for a reboot was to get around potential problems with old device drivers that didn't play well with the 286. The 80286 does
          not allow an OUT instruction to be followed by another I/O
          instruction unless the OUT is immediately followed by a JMP
          SHORT $+2 instruction to introduce an I/O wait state.  Many of
          the 8088/86 device drivers were written before the 80286 was
          introduced and do not contain correct 80286 coding technique, which may cause system hangs if running the system in 286 mode. If you come across any system hangs or other problems using such device drivers, run the HotShot/286 in 8088/8086 mode. 
        Cached Memory Settings for Base (0-640K): 
        SW1  SW2  SW3  Cached Area
---  ---  ---  --------------
OFF  OFF  OFF  Cache Disabled *
ON   ON   OFF  0-256 KB
ON   OFF  ON   0-512 KB
ON   ON   ON   0-640 KB 
         * = Default Setting
 
         Cached Memory Settings for Extended (640KB-1024KB): 
        SW4  SW5  SW6  SW7  Cached Area
---  ---  ---  ---  ---------------
OFF  OFF  OFF  OFF  Cached Disabled *
ON   OFF  OFF  OFF  0C0000-0CFFFFH
ON   ON   OFF  OFF  0C4000-0D3FFFH
OFF  ON   OFF  OFF  0C8000-0D7000H
OFF  ON   ON   OFF  0CC000-0DBFFFH
OFF  OFF  ON   OFF  0D0000-0DFFFFH
ON   OFF  ON   OFF  0D4000-0E3FFFH
ON   ON   ON   OFF  0D8000-0E7FFFH
ON   ON   ON   ON   0DC000-0EBFFFH
OFF  ON   ON   ON   0E0000-0EFFFFH
OFF  OFF  ON   ON   0CC000-0EFFFFH
ON   OFF  ON   ON   0A0000-0AFFFFH
ON   OFF  OFF  ON   0A0000-0B7FFFH
ON   ON   OFF  ON   0CC000-0DBFFFH and 0A0000-0AFFFFH
OFF  ON   OFF  ON   0CC000-0DBFFFH and 0A0000-0B7FFFH
OFF  OFF  OFF  ON   0D0000-0DFFFFH and 0A0000-0B7FFFH 
         * = Default Setting
 
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