William Donzelli wrote:
Umm 6 bits is
perfect for BCD, look at IBM's 1620 : 4 bits BCD, 1 bit
sign flag/length flag 1 bit parity
Very inefficient. I hope you are not serious.
Back in the 1960s, most data was numeric, due to banking. It may still be
the dominant form (with maybe porn mpgs a close second).
Lets call this multi-media to include music downloads. If I want porn
rather get a DVD
than a mpg. :)
Each field of a
database might have 10, 12, perhaps 16 BCD characters. Why on Earth would
you want a sign bit associated with each one? If the field even needed a
sign, only one would be needed. Parity? That is the job of the memory
controller - having the processor figure out parity is just a waste of
CPU.
Well the 1620 was a variable length machine ... A sign/flag bit made
more sence at the time since
you only had as many BCD digits as you needed.
You need to realize that back in the 1960, each bit was
counted with a
price tag. A medium sized mainframe might only have 64K with a few tens of
megs on disk. A batch might take all night to run, with no time for
fooling around with extra bits.
The extra bits were hidden but parity was the price you paid for core
memory at the time
for error checking.
Basically, sixbit died when it should have. The DEC 36
bit line suffered
from really bad timing (the S/360 was being planned, unknown to DEC, when
the PDP-6 was being wheeled out. The S/360 made the world 8 bits, and
signed the PDP-6/10s death certificate.).
I am not a IBM fan... I support 9 bit bytes. ( Bytes for a lack of
better name ).
The PDP-6/10's may of supported them but other than the CPU I am building
I can't think of any other computer using them.
(Well I got some of the hardware already ... 1'st build the case to hold
the front panel)
To clairfy about IBM and bytes from a marketing standpoint it was a way to
misslead the potential computer buyers from my veiw point that with the new
marketing terms -- byte vs words , 32 vs 36 bits so that IBM's products
would
look better compared to the 7 dwarfs at the time. Just like stating raw
clock speed
today for marketing. I can buy a N GHZ machine but can anybody tell me
the real
speed of instruction abc on data xyz?
Ben alias woodelf