Why are still not at 64 bits

Ric Werme ewerme at comcast.net
Thu Feb 15 14:19:35 EST 2007


From: "Jon 'maddog' Hall" <maddog at li.org>

>>   What would AMD64 (or even the Alpha's feature set) do for the
>> typical end-user?  I'm talking about the people browsing the web and
>> writing email and downloading music and looking at porn.  These people
>> aren't doing 6-way SQL JOIN's or loading the entire US phone book into
>> RAM.  Their PC is plenty fast enough, so long as you clean out all the
>> adware and viruses and other badware.

I've never looked at the AMD64 instruction set, but 64 bit pointers bring a
lot of overhead to code.  I used an Intel i860 at Alliant, which was a 32 bit
RISC chip.  I could load a pointer with two instructions.  On Alpha, which
also has 32 bit instructions, the convention is to access the data by
accessing the pointer from a block of memory set aside for stuff like that.
That requires maintaining a register with the address of the block and
restoring it after library calls and other whatnot.  Pretty ugly, I've
always thought.  Also having a 64 bit address space means winding through
more levels of page maps.  All in all, I don't think there's anything
inherently faster about a 64 bit CPU unless you need more than a 32 bit
address space.  (There were a lot of reasons to dislike the i860 and Intel's
support for it has parallels with the CPU-that-must-not-be-named.)

>Other things also affect it, such as the cost of RAM.  The 64-bit
>Translation Look-aside Buffers (wow, it has been a long time since I
>thought about those) for the Alpha were bigger than most main memories
>of desktops in the 1980s.  And that 64 KB memory cost 100K dollars in
>1968.

A dollar a byte of core memory was a good deal in 69/70.  Easy price
point to remember.  Can you imagine holding 1 GB DDR or USB memory back
then?

>The Alpha was a space heater.  It took no bones about sucking down
>electricity.

Yeah, but at trade shows I heard people would leave the CPU board
exposed and invite people to touch the heat sink.  40 watts was a
lot then, but didn't require heat pipes or on-CPU fans.  I recently
upgraded my Compaq Deskpro (1 Ghz Pentium III) to an adequate "current"
AMD 3500+ system.  My Deskpro idled at 50W, this beast is 150W or so.
I may go back to the Deskpro eventually for 24/7 tasks and use this
system only when I need it.  OTOH, it is my only Windows (2000) box and
can't handle 1600x1200 graphics, so I may stay here.

Someone at DEC/Compaq/HP had a dual CPU CPU-that-must-not-be-named system
in his office.  We got tired of him talking about how hot it was every
day a lunch.

> *I did a calculation once that if you filled a one GigaByte disk for
> every second of the day, every day of the year, it would take over 5,386
> years to fill those disks with 2^64 bytes of data.**

TeraByte disks are coming!  TB disks that take one second to fill will
take a while longer....

> **Yes, I did take into account leap years, and unlike Microsoft, I know
> that every four hundred years we skip one.

Umm, every 400 years we _observe_ one instead of skipping one every 100
years.  It might have something to do with global warming.

	-Ric Werme



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