[plug] Free CD linux - any good ?

[David Griffiths]

Hmm... just looking on the web for info here...

Kevin wrote :

>You were right the first time (more or less) - you get 20 bits of
>address space in a 16 bit 8088/8086/V20 (note - no difference between
>the 16-bit 8086 and the 8-bit 8088) because you actually address 4-bit
>space (16 byte) paragraphs.  A very silly idea when it comes to
>assembler.  I think the 386SX has the same 32 bit address space as the
>DX, only it has to pump out the address in two clock cycles having a
>very limited number of pins, half of which are multiplexed to different
>uses.

http://www.pcguide.com/ref/cpu/fam/g3I386SX-c.html lists address bus width
as 24 bits (16MB addressable mem) and data bus width 16 bits for the SX.
The page for for the DX lists address bus width as 32 bits (theoretical max
mem of 4GB!!) and databus as 32 bits. My understanding is the narrower SX
data bus means the SX takes two looks at memory to grab 32 bits worth of
data instead of 1 for the DX resulting the 20-25% performance loss of the
SX over the DX that the web page mentions.

Looks like the SX was released _after_ the DX which I didn't realise before
- to be compatible with the cheaper 286 chipsets.

>  The fact that 386SX mobos were usually issued with 4 * 30-pin
>DRAM slots does tend to restrict you to 16 MB though.
>
hmm, see above... I think that 24 bit address bus width will be the reason
for the 4 slot limit. The mind boggles at the thought of a 386DX with 4 GB
ram though. That would be a few slots! :-)


Dave G.



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  David Griffiths                             griffith at environ.wa.gov.au

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