stever@videovax.UUCP (Steven E. Rice) (08/12/86)
In article <950@hoptoad.uucp>, John Gilmore (gnu@hoptoad.uucp) writes (referring to article <829@edison.UUCP>, by David C. Albrecht [dca@edison.UUCP]): > David, you are absolutely right. Video RAMs are the obvious technical > solution -- they give the CPU all your memory bandwidth and let you run > the monitor at damn near any scan rate it can handle. Unfortunately, > Amiga did not built in the video RAMs, nor did they provide you with a > monitor that can handle a fast scan rate. Retrofitting them is more > trouble than it's worth. Get a long persistence monitor and wait for > the Amiga ][. > > PS: If it's any consolation, I tried to talk Atari into using video > rams for their next products and I don't think *they* will either. > (Something about them costing a few cents more than regular rams.) There is also an architectural issue. If you use video RAMs, the bits to be displayed must be in a contiguous memory area. When the video RAM moves a row of bits to its output shift register, it takes (sets of) 256 adjacent bits at a time. On the other hand, if you use standard memories, you can address one "word" at a time (whatever width the system uses). The video "window" chips take advantage of this to assemble displays from pieces pointed to by a display list. You get easier access to the display memory with video RAMs, but the tradeoff is that you MUST bitblt your display together. If your processor cannot effectively perform high-bandwidth transfers, the standard architecture may be a better match to your needs. Steve Rice ---------------------------------------------------------------------------- {decvax | hplabs | ihnp4 | uw-beaver}!tektronix!videovax!stever
rogue@well.UUCP (L. Brett Glass) (08/14/86)
Perhaps the best tradeoff is to use V-RAM in combination with a high-powered blitter and shift-register chip, as is done on the new TI 340. The results make even an Amiga look slow. <rogue>
hindmost@mit-trillian.MIT.EDU (Brian R. Murphy) (08/17/86)
In article <1626@well.UUCP> rogue@well.UUCP (L. Brett Glass) writes: >Perhaps the best tradeoff is to use V-RAM in combination with a high-powered >blitter and shift-register chip, as is done on the new TI 340. The results >make even an Amiga look slow. <rogue> Wouldn't generic dual-ported RAM allow fast and flexible access by both the processor and the VDC (or other I/O chips)? I think this is cheaper than V-RAM, though I may be wrong. Using this in the Amiga would be a really big win, since you could put the Blitter and other chips on a separate bus (well, maybe not the blitter; you wouldn't want refresh to slow it down). Then, with probably little change in the chips themselves, you could step up the processor to ~14.414Mhz, get rid of interlacing, and end up with less conflict between the processor and other chips. Is this possible? (I'm not really into hardware, so I don't know). Brian Murphy hindmost@athena.mit.edu ...ihnp4!eddie!athena!hindmost