kds@intelca.UUCP (Ken Shoemaker) (01/14/86)
> > > ... There's no reason why bitblt hardware can't use virtual memory the > > > same way the cpu hardware does, although it adds cost and complexity. > > > > Well, if you are willing to make virtual memory hardware that responds > > in "real time..." I'd think that would be more expensive than just having > > more memory! > > You miss my point: your cpu needs "real time" response too -- a few hundred > nanoseconds at the most, usually -- but it has no problem with page faults. > The process that was running simply gets suspended until the page is on hand. > There's no intrinsic reason why bitblt hardware couldn't do the same thing, > although it's not common. Perhaps I was thinking about virtual screen memory, i.e., when it comes time to refresh a certain part of the screen, you have to wait for the disk to get accessed and memory updated to show what is supposed to be on the screen. > > > > With memory costs on the wane (or at least they were until the government > > got involved) I don't see the use of color displays going any way but up, > > even with the more expensive tube. > > Memory costs are not the only problem; to update things at the same speed, > you also need several times the bitblt bandwidth. And several times the > backing-store bandwidth. Those are not as easy to come by as bigger memory. > I seem to remember on an old pdp11/70 system, that a single terminal going at 38kbaud pretty much maxed out the system, with respect to file access, not communication link speed...I mean, you do need to send useful stuff to the screen! If you don't rely on your system CPU to do the bit-blt, i.e., you have specialized hardware to do it, I don't imagine that you'd have too much trouble keeping up with the bandwidth a cpu is able to send useful stuff. Add to this the availability of so-called video rams that dramatically increase the bandwidth of memories used for screen refresh and I think that most of the bandwidth problems go away. As for backing store, you need not have any more if you are just trying to show the same old, boring B/W screen. Adding highlighting, et al., is a function of the program enhancing existing data. Unless I have it completely wrong, any application that requires more backing store is one that would be difficult with a mere B/W screen. Finally, perhaps I'm an optimist, but I'd like to think that economies of scale will do to high-res color monitors what it has done to most anything else electronic. It wasn't that long ago that you couldn't touch a terminal for quite a bit more than they now cost. Even 12" monitors were pretty pricy. Whatever... -- remember, if you do it yourself, sooner or later you'll need a bigger hammer Ken Shoemaker, Santa Clara, Ca. {pur-ee,hplabs,amd,scgvaxd,dual,qantel}!intelca!kds ---the above views are personal.