Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rutgers!ames!ucbcad!ucbvax!CORY.BERKELEY.EDU!dillon From: dillon@CORY.BERKELEY.EDU (Matt Dillon) Newsgroups: comp.sys.amiga Subject: Re: Help: definitions and terminology Message-ID: <8704192056.AA07352@cory.Berkeley.EDU> Date: Sun, 19-Apr-87 15:56:32 EST Article-I.D.: cory.8704192056.AA07352 Posted: Sun Apr 19 15:56:32 1987 Date-Received: Sun, 19-Apr-87 22:35:29 EST Sender: daemon@ucbvax.BERKELEY.EDU Lines: 194 >Amy vid chip The Amiga's Video chip. >video gate array ??? >blitter A device which offloads graphics tasks from the main processor. As far as I know, there are two terms: 'blitter', and 'bimmer'. A blitter is basically a DMA processor which can do copies between rectangular areas on a bitmap. This is slightly more complicated than a standard memory copy as the rectangular areas can be any width and height, and their upper left hand corner need not be the upper left hand corner of the bitmap. Blitters usually have the ability to draw 'lines'. A bimmer is a more powerful version of a blitter. The Amiga's blitter is really a medium scale bimmer, since it can perform arbitrary login operations on the bitmap data. We call it a blitter because the term stuck. In anycase, as far as the Amiga goes, it's blitter can do any arbitrary logic operation from three sources to one destination. The destination can also be included in the login operation by specifying it as one of the sources. >copper The Copper is a simple two instruction co-processor in the Amiga. The Copper can (A) Wait for the video chip to get to a particular scan line on the display, and (B) stick some immediate data into almost any IO register. The Copper is thus used to change video modes on the fly (i.e. change the color registers, sprite pointers, video modes, etc....). Again, the whole idea is to offload work from the 68000. Although the Copper steals cycles from the 68000, it runs a very small percentage of the time (less than 3%). To do all the stuff the Copper does in the 68000 would take considerably more time (10%+). >chipmem Chipmem refers to the area of memory that the custom chips can access with their DMA. Currently, the custom chips have only enough address lines to access the lower 512K of memory. Any custom chips which steal processor cycles only do so when the processor is attempting to access this area of memory. The 256K expansion you stick in the front of your Amiga gives it exactly 512K (not including the OS, which has its own 256K). >fastmem FastMem refers to any expansion memory you might add to your Amiga beyond the first 256K expansion you stick in the front of your machine. That is, any RAM beyond the 512K mark is fast memory. The term 'fastmem' comes from the fact that the 68000 can run at full speed when referencing FAST mem no matter how many cycles the custom chips are stealing from CHIP memory. Needless to say, the WCS (Writable Control Store) that the OS is loaded into is 'fastmem', although effectively ROM. >graphmem Graphics memory? Generic term meaning the memory available to some graphics device. On the Amiga, this is the lower 512K portion of memory. >color look-up table >color registers Both mean the same thing. If a given pixel on the screen is made up of, say, 4 bits (4 bit-planes), then it can assume one of 16 colors normally. (exception: HAM, see below). On the Amiga, there are 4096 colors available. You want to be able to pick 16 out of the 4096 colors to use for that screen. Thus, your color look-up table would have 16 entries in this case (each entry being able to specify any of the 4096 colors). Each entry represents a combination of bits that are 'on' for that pixel. Some times 'color look-up table' means the lookup table is in RAM rather than in hardware registers. >X (or X Windows) >SunNews These are windowing systems used on workstations. >Agnus, fat agnus, paula, portia, diane, etc. The Amiga's custom chips, with some hardware terms sprinkled in. >SUPER_BITMAP Refers to a window containing a bitmap which is much larger than the window, so you can only see a small part of the bitmap in the window at one time. >What are the various ways of representing a monitor image in memory? >bitplanes? On the Amiga, it's bitplanes. E.G. if each pixel is 5 bits, then the screen has 5 bit planes. Each bitplane is a contiguous segment of memory and can be referenced independantly of other bitplanes. Other machines might, for instance, stick all the bitplanes together in one big chunk so each BYTE represents the information required to display one bit. I for one do not like this method because it is difficult to provide for expansion beyond 8 bits per pixel without changing the way memory is organized (i.e. to go to 16 bits per pixel, you have to now make each word reference a pixel). Whereas with the bitplane approach, you simply add another bitplane. Note that the two methods do not take the same memory bandwidth to display. Whereas the bitplane approach takes a variable amount of bandwidth, the chunky approach always takes the maximal amount. Of course, if the maximal amount can be handled without slowing down the processor, this does not present a problem. >each dot has it's own contigous group of bits for color (chunky memory)? >chunky-planar? See above. It's a contiguous group of bits (as in one byte represents a pixel), or broken up via bitplanes. >HAM? >Can anyone give a 2 or 3 paragraph explanation of just how HAM works? >How about any other "exotic" memory map scheme? HAM is a 6-bitplane low-resolution video mode on the Amiga. The difference is that bits 5 and 4 (543210) now control how the remaining four bits are used. 5 4 3...0 0 0 color of pixel is that found in the color register 0-15 (as if you had 4-bitplane normal video). 0 1 use the color of the pixel to our left, but modify the BLUE using our 4 remaining bits (3210). 1 0 same as 01, but the RED color is modified 1 1 same as 01, but the GREEN color is modified. Thus, you can effectively get all 4096 colors on the screen. By making proper use of your 16 'static' colors, you can get to any of the 4096 available colors within 2 pixels... The idea behind this is that in many pictures, one has a gradual change in color. HAM mode can allow you to make this gradual change without wasting ANY color registers. For those parts of the pictures which have sudden changes, you can use a color register and 'jump' to that color... or close enough to that color that nobody would notice the difference. >What is bandwidth (I need a really exact definition of this one, it's all >kind of fuzzy in my head, must not be enough bandwidth, eh?), and how does it >relate to graphics display? There are two kinds of 'bandwidth'. One refers to the 'bandwidth of your monitor' (basically the resolution it can support). The other refers to MEMORY bandwidth... how many bytes/sec can be transfered from main memory. An Amiga 1000 has a total memory bandwidth of about 7MBytes/sec. (memory access every two cycles of a 7.14Mhz 68000 = 3.57M access/sec, @ 16 bits / access = 7MBytes/sec). (correct me if I'm wrong). >CLIPPER Fairchild's 32 bit microprocessor. It really screams. Burst and tight loop operation is better than a 68020. Normal operation is equivalent to a 16Mhz 68020. I believe the the Clipper has an MMU, FPU, and cache built in. >AM29000 A joke? >TurboAmiga Coined by ASDG, I believe. Refers to an Amiga with a 68020 in it, usually with some 32-bit wide memory running at 16Mhz. >the AT&T blitter beast No idea. >other blitters (how about a knowledgeable comparison?) the Atari ST will soon have a blitter, but rumor is that it will be a very simplistic one. TI has a really awesome bimmer, but I don't have the specs on it. I know of no computers which use it but obviously some must somewhere. -Matt