Lisa Hancock wrote:
>> Time sharing required a facility known as "Dynamic Address
>> Translation". I wonder if this was patented.
> The process? "impossible".
> A specific _circuit_ that did it? possibly.
Time sharing in its simplest form needs nothing more than a periodic
interrupt to invoke a task switcher. Hardware to manage user memory
space is certainly nice, but not manditory, particularly if the users
can be constrained (by compiler or application) to run in only the
memory space allocated to them.
"Dynamic Address Translation" is an impressive phase, but early
machines had nothing more than a relocation register and a protection
register. The user's memory addresses were summed with the relocation
register to get a physical address. The protection register set an
upper bounds on the user's memory access and caused a trap or fault to
the kernel if exceeded.
Often as not, "dynamic address translation" was added to machines to
overcome hardware memory space limitations rather than to implement
timesharing.
> Writing the claims broadly enough to apply to different physical
> address bus architectures would have been a challenge.
>> include it in its original System/360 line in 1964 and not support
>> timesharing, but General Electric did and their machines were used for
>> early timeshared computers. IBM later added this to its System/360
>> model 67 and its System/370 line. Time sharing proved to be a lot
>> harder to implemented than first predicted; it was a heavy CPU and
>> meory drain which was a problem on the technology of the 1960s.
I disagree. I installed a fully functional 8-user timeshare system
on a PDP 8 with 12k words of memory back in 1972. The early
Unix and Decsystem 10's were amazingly efficient for the resources
available then.
Anyone interested in hearing about this stuff from the people that
actually did it should review the early years of alt.folklore.computing.
Lots and lots of good posts.
>> Some in the early 1960s predicted time sharing would allow
>> "democratization" of computer services, by allowing acess by anyone
>> through a terminal to an expensive computer. Some of these published
>> predictions described the Internet as we have it today [in 2007] as
>> being available in 1990, it took another full decade for that to come
>> to fruition.
I've always been amazed that not a single science fiction writer *got*
the internet. All of the SF saw the future as monolithic central
computers.
Jim Stewart (jstewart@jkmicro.com)