On Sun, Jan 31, 2010 at 07:29:00PM -0500, Jerome H. Fine wrote:
Dave McGuire
wrote:
And you do realize "PDP-11" spanned some two
and a half decades
and more
than a dozen implementations with a huge range of processing power
ranging from "wimpy" to "big clanging brass balls", right?
Yes, but the PDP 11 was designed to have raw power from the original
design. OK, they goofed on a basic address space of 18 bits.
16 bits, actually. The two MMU architectures extended that to 18 and
22 bits. I wouldn't call it a goof considering the first one came
out in 1970. For a small lab minicomputer in 1970, 64KB isn't bad at
all.
Considering the cost of CORE memory in 1970, 64KB was
much larger than any PDP-11 at that time. 8KB was a
common system. Even up to around 1975, I don't think
there was an MMU available in any case. Does anyone
know when the MMU was first used with more than 64KB
of memory for the system?
As for total memory available to use for temporary
work space, when I run Ersatz-11 under WXP on a
system with 4 GB of physical memory (I agree that
WXP wastes almost 1 GB of that memory),
Not the fault of Windows. For a 32 bit PC system with 4 GB of
RAM, up to 1 GB of RAM is 'lost' because up to 1 GB of
the address space is used for the PCI address space (i.e.
memory mapped access to peripherals[0]). It can be quite bit
less (such as 500 MB), or up to the full 1 GB - that depends
on the specific hardware.
Kind regards,
Alex.
[0] Although with current PC mainboard, a lot of those 'periphericals'
are on the same mainboard, even part of the mainboard chipset.
--
"Opportunity is missed by most people because it is dressed in overalls and
looks like work." -- Thomas A. Edison