dale@wucs.UUCP (Dale Frye) (08/12/85)
In Byte they show a picture of the Amiga motherboard with two 27256 ROM's and
room for two more. The picture also shows only 8 41256s. Is the memory bus
only 8 bits wide? However in a new magazine called AmigaWorld there is a
picture of the motherboard with 16 41256s. I couldn't see any ROM but then the
disk drive was in the way. A friend who attended a local dealer roundup by
Commadore told me that there isn't any system ROM. Instead the system is loaded
on power-up into RAM and then is write-protected.
Questions
1: How much real ROM exists and what is in it.
2: How much RAM exists and how does the write protection work. (i.e. can the
size of the protected area be programmable)
MOST IMPORTANT QUESTION!!!!
3: Is the memory data path 8 or 16 bits wide!!!!!!!!
Dale Frye @ Washington University in St. Louiscsc@watmath.UUCP (Jan Gray) (08/15/85)
In article <1087@wucs.UUCP> dale@wucs.UUCP (Dale Frye) writes: >In Byte they show a picture of the Amiga motherboard with two 27256 ROM's and >room for two more. The picture also shows only 8 41256s. Is the memory bus >only 8 bits wide? However in a new magazine called AmigaWorld there is a >picture of the motherboard with 16 41256s. I couldn't see any ROM but then the >disk drive was in the way. A friend who attended a local dealer roundup by >Commadore told me that there isn't any system ROM. Instead the system is loaded >on power-up into RAM and then is write-protected. Look closer. Those DRAMs have *18* pins. They are almost certainly 64K x 4, not 256K x 1, so the Amiga has a 32 bit bus (which is absolutely necessary to get the high bandwidth to video if you work it out). I will also speculate that the picture in AmigaWorld is of the new Amiga with "writable control store" (Oh God!) which uses the extra 256K for the OS. >MOST IMPORTANT QUESTION!!!! >3: Is the memory data path 8 or 16 bits wide!!!!!!!! 32 bits. I think. Jan Gray watmath!looking!jan Looking Glass Software, Waterloo 519-884-7473
michaelk@azure.UUCP (Mike Kersenbrock) (08/15/85)
> Questions > > 1: How much real ROM exists and what is in it. > > 2: How much RAM exists and how does the write protection work. (i.e. can the > size of the protected area be programmable) > I have no idea, but if I were them, it sure would be handy (during OS development) to have the OS in writeable memory (either in temporary added RAM or "mapped-in" using an in-circuit uP emulator (my employer makes very good ones (plug) which we use ourselves)). It will be interesting to see what version is the "production version" and to see if it stays that way. > MOST IMPORTANT QUESTION!!!! > 3: Is the memory data path 8 or 16 bits wide!!!!!!!! > > > Dale Frye @ Washington University in St. Louis The block diagram in Byte magazine showed seperate data busses for the (UVEP)ROM and the RAM with a bit of circuitry between them. Because the 68000 is 16-bit WORD oriented, and because you can use paging-mode tricks with DRAMs (you double-CAS the parts), you COULD make 8-DRAMs do a very decent job with word-accesses. Not having the Amiga schematic handy :-), I wouldn't know if they actually do this. Mike Kersenbrock Tektronix Software Development Products Aloha, Oregon
tim@callan.UUCP (Tim Smith) (08/27/85)
> In Byte they show a picture of the Amiga motherboard with two 27256 ROM's and > room for two more. The picture also shows only 8 41256s. Is the memory bus > only 8 bits wide? However in a new magazine called AmigaWorld there is a 8 256k chips makes 256k bytes, which is what the most common claim is for total ram. It has been speculated that they are using fast rams, and doing TWO memory cycles two get the 16 bits needed for the 68k. It has also been claimed that they dropped the roms and use ram loaded at startup. This could explain why the later board had no ROMs but another set of 8 RAMs. -- Tim Smith ihnp4!{cithep,wlbr!callan}!tim