At 05:32 PM 10/27/98 -0800, John R Pierce wrote:
>The 286 had a 24 bit address bus but a 16 bit data bus. Nothing about the
286
>was 32bit.
According to "Great Microprocessors of the past", it did have some 32-bitness:
http://infopad.eecs.berkeley.edu/CIC/archive/cpu_history.html
Although this was largely acceptable for assembly language, where control of
the segments was complete (it could even be useful then), in higher level
languages it caused constant confusion (ex. near/far pointers). Even worse,
this made expanding the address space to more than 1 meg difficult. The 80286
(1982?) expanded the design to 32 bits only by adding a new mode (switching
from 'Real' to 'Protected' mode was supported, but switching back required
using a bug in the original 80286, which then had to be preserved) which
greatly increased the number of segments by using a 16 bit selector for a
'segment descriptor', which contained the location within a 24 bit address
space, size (still less than 64K), and attributes (for Virtual Memory support)
of a segment.
+----------------------------------------------------------+
| Jud McCranie [EMAIL PROTECTED] or @camcat.com |
| |
| Where a calculator on the ENIAC is equipped with 19,000 |
| vacuum tubes and weighs 30 tons, computers in the future |
| may have only 1,000 vacuum tubes and perhaps only weigh |
| 1.5 tons. -- Popular Mechanics, March 1949. |
+----------------------------------------------------------+
