sch (03/11/83)
I have heard (at least third hand) that one of the Bell has
announced or is planning to announce a workstation containing:
a BLIT terminal - snazzy bit map 68000 with hardware
raster op
a 2B Cpu - 32 bit super chip hard to define
as mini or micro.
a 2B to handle I/O to terminals/disk
hard disk - what kind?
That is all I have, no idea as to availablity, price, performance
any thing else.
Am Interested,
S. Hemminger
...decvax!{genradbolton,wivax}!linus!sch
...allegra!linus!sch
sch@linus.uucp (if you have internet we do)guy (03/12/83)
I noticed that the workstation mentioned has a BLIT (with 68000) AND a 2B (Bellmac-32? Rumor has it that Bell will release its 3B-5 Bellmac-32 based UNIX box) CPU. I have noticed that several small systems - including single- user workstations - have a separate processor to control the display AND do NOT have the video memory directly accessible to the CPU. If you have the processor doing the text editing/formatting or the graphics or whatever able to directly access video memory, you can update your screen a LOT faster. The Alto, the Star, and the Lisa all have the driven directly from CPU memory, and they all have sexy text and graphics software. Is there any reason why a lot of systems being put out now have a "thin wire" connection between the processor and the display? Almost all (if not all) of those systems have a shared-memory connection between SOME processor and the CRT controller - but a lot of them have something like a Z80 or so to control the display, and force the 8086 or 68000 or whatever to shove the characters or bits through a relatively slow pipeline to the memory. Is there a reason why this is done? Is it the extra cost of the dual-ported memory? Guy Harris RLG Corporation ...!decvax!mcnc!rlgvax!guy
tjt (03/18/83)
Part of the reason for not allowing the main CPU direct access to display memory on systems with separate graphics processor cards is indeed the additional cost (both in terms of dollars and increased access time) of dual-porting this memory. Actually, the memory is dual-ported already (to the graphics processor and the raster-display hardware). However, the main reason for including a separate graphics processor (Z-80, 68000, or whatever) is to relieve the main processor of the responsibility of performing much of the time-consuming, low-level graphics processing. In particular, painting characters, drawing lines, arcs, boxes, et cetera. For these operations, the data compression achieved by the high-level commands as opposed to low-level access to bits or bytes in the display memory is quite high and I don't think display performance suffers. However, if you really do need to twiddle every bit (e.g. for imaging) any "thin-wire" approach will involve extra overhead, no matter how efficient the wire is (e.g. shared memory between the host and graphics processors). This effect is similar to the difference between driving a Versatec in "printer" mode as opposed to "plot" mode: because you have to supply all those bits in plot mode, it is difficult to keep the paper moving at full speed. I believe that in most cases the use of an additional processor for low-level graphics operations will provide an overall performance improvement by using less host processor resources. After all, if both processors are busy then you are getting some extra CPU cycles, although some of the extra cycles are being dissipated in communication protocols.
guy (03/30/83)
True, but one problem with a lot of systems, especially ones which have only character displays, is that 1) the "graphics processor" is a little Z80, which has less power than the host (an extreme example is the 8080 in my VT100 attached to our 11/780) and 2) the wire is 9600 baud worth of thin. Screen editors can paint the screen a *lot* faster than 960 characters a second; if you're continuously reformatting the current paragraph to keep it up to date as text is inserted you want direct access to the video memory. I guess I didn't state my question well; I was more wondering about systems used for text and business graphics, not SUN/Apollo/etc. type workstations which were doing more sophisticated graphics. The Convergent Technologies AWS Turbo Graphics workstation has the main processor handling text display with the text image coming from its memory, and has another processor to handle the graphics, so a graphics processor is useful even for business graphics. I just don't want to be processor-to-screen-memory bandwidth limited when updating the text display. Guy Harris RLG Corporation seismo!rlgvax!guy