aic@pucc-i (Craig Norborg (aka Doc Pierce)) (11/15/85)
Amiga,
I have just finished talking to the dealer I bought my Amiga from
and heard some interesting rumors and such from him. He was talking to
some of your engineers who frequent CompuServe and they were telling
him that if you get the ram that goes over the first 512K boundry, such
as the Tecmar board, that the ram will actually run 2 times faster than
that in the first 512K! From what I have understood, the machines
first 512K was supposed to hold the fastest ram, which is true? What
will be the advantages/disadvantages to getting the extra 512K?
Also, could you confirm/deny the possiblity of substituting the
68000 contained within the machine with a 68010? Will this hurt or
improve the machines speed, and is it possible?
Once again, for those of us who have already bought Amiga's, could
you state the company policy for hardware/software updates?
Thanx in advance,
--
Craig Norborg (aka Doc Pierce)
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Lafayette IN 47904hr@uicsl.UUCP (11/17/85)
Someone referred to the Tecmar board and the external memory.
Does anyone know when it will be available? And for how much?
For that matter, has ANY 3rd party option hit the market yet?
harold ravlin
{ihnp4,pur-ee}!uiucdcs!uicsl!hrbobp@amiga.UUCP (Robert S. Pariseau) (11/17/85)
The speed of RAM placed on the expansion bus depends, to some extent, upon the quality of it's implementation. The Amiga architecture ALLOWS expansion bus memory (that is memory over the first 512K) to run at full bus speeds. I don't know of anyone implementing expansion bus memory who expects to provide slower memory -- but you never know. The first 512K of memory, known as Chip memory to the AllocMem() function, is the only memory the custom chips can get to. It is possible to configure your Amiga such that the bandwidth out of chip memory is largely consumed for video display. In this high data rate mode of operation, the 68000 yields to the higher priority needs of the system DMA channels such as the video. This is called memory "contention". [For newcomers: There is NO contention in the 320x200, 16 color mode normally used for games, or in the 640x200, 4 color mode normally used for Workbench and text functions.] There can NEVER be contention in the Writeable Control Store (where the system firmware is kept) or in the expansion bus memory [ignoring, of course, any contention BUILT-IN to stuff on the expansion bus]. For this reason, the AllocMem() function identifies expansion bus memory as Fast memory. Note that Fast memory can NEVER be faster than Chip memory in the no-contention modes of operation. As a programmer, you need to be sure that data structures you make which are directly referenced by the custom chips are allocated in Chip memory. This means, don't statically allocate them, or place them on the stack, since that may place them in Fast memory depending upon what else is in the machine --> ergo, your programs stop working when people add expansion bus memory. For V1.0, you must dynamically allocate your Chip structures in Chip memory -- moving data from your static structures as necessary. For V1.1, the system loader recognizes flags in the program image which say that certain portions of the program MUST be loaded into Chip or Fast memory. If a preference is not specified, then Fast memory is generally used first -- maximizing system resources. The program flags can be set using the new Atom utility which is applied to your object binary files BEFORE you link them with Alink. [This means you can set the flags on routines which are then placed in libraries so that anyone can use your routines without having to know special rules about where they can go.] Note that you STILL can not safely allocte Chip structures on the stack. ----------------- Commodore can NOT recommend that you replace the 68000 in your Amiga with any other processor. This warning is brought to you by our good friends at the FCC who insist that we test any hardware configuration against Class B restrictions before we recommend it to anyone. That aside, we HAVE heard from folks who (in STRICT VIOLATION of their warranty) have opened up their Amigas and replaced the processor. Their reports say that the system software works fine unless you have a buggy program that generates one of the 68000 exceptions that changed for the 68010. The trap catcher and the stuff that puts up alerts and gets you into ROMWack is not prepared for the new-fangled stack frame put out by a 68000. Note that there is a routine called GetCC() in EXEC which gets you your processor condition code in a manner that is compatable across the 68000 family. This is the only normal-operation incompatability that needs to be addressed.