MKrieg@UMASS.BITNET.UUCP (02/25/87)
/\/\ark <riegsman -=*=-- 561 Hampshire College -=*=- Amherst, MA -=*=- 01002 I've been tempted several times in the last few days to respond to "things" that have been posted here, but have so far refrained. But, ... RE: Disk conversion... The original disk ][ controller ( the one that runs your old-style 5 1/4" drive(s)) has almost no smarts of its own. You can literally intercept the data coming from the disk on a bit-by-bit basis. While this makes it seem like you might be able to do anything you want with an Apple and a 5 1/4" drive, 1) the processor is not -quite- fast enough to use the data as it comes in...the best you can do is buffer it for later and 2) the disk controller, because of it's lack of brains, can "get lost" on any given disk track if the data is not formatted to prevent it. Specifically, no more than two bits in a row may be zero. (Under the 13 sector controller [remember them!] no more than one (!) bit could be zero in a row.) The disk driver program changes data from a happy 8-useful-bits-per-byte to a somewhatskewed 6-useful-bits-per-byte format before it writes it out, and de-converts when it reads it back in. You cann write your own disk driver, but be very careful about timing. (this is how every single program ever released for the Apple up until about three years ago had its own disk format...hence the need for "bit-copiers") If you try this, one final word of advice: PUT THE HEAD BACK INTO THE READ MODE BEFORE TURNING OFF THE DRIVE MOTOR!!! Geoffrey Engelstein and I (ever hear of a game called "Starblaster" from Piccadilly Software?...we wrote it.) spend about 45 straight hours trying to find that one. RE: Relative Clock Speeds THe 6502 is a "pipelined" processor; each part of it can do something at once. The memory acces part can be fetching the next piece of data *while* the Arithmetic Logic Unit is performing an "add" operation. A 1Mhz 6502 is -generally- (no flames, PLEASE!) about as fast as 3-4Mhz Z-80, because the Z-80 can only to one thing at a time, ie, fetch an instruction, fetch a data value, add, deposit the value, etc.. We (Apple folks) are blessed (!??) with the hand-coded magic of one Mr. Steve Wozniak. This man seems to have some kind of obscure mutation that allows him to write faster, smaller, more efficient code than anyone else. So beyond pure processor /speed/ we have the work of a brilliant man lurking in each machine. RE: High-res character Generators... Well, it seems that this kind of thing is in high demand. The //gs has a *really* *nice* on in ROM, but that's quite a large investment to make for a piece of utility software. If anyone is interested, I would be willing to post a reasonably robust and complete HRCG (Shareware...$5) to the net, DOES ANYONE WANT THIS? (write to me, so if no one else does, I can send it just to you.) I could also post a couple of fonts I've got, again, only if people want this. I've been working with Apples (doing assembly language development work) since about '79, so if anyone has any weird assy lang questions, I'd be happy to try and help. ,-Mark-Kriegsman--(see-diagram-2)---------------. Claimer: 1) you can only act once. BITNET: mkrieg@umass 2) einmal ist keinmal. CSNET: mkrieg%hamp@CS.UMass.EDU '. nothing /really/ matters. INTERNET: mkrieg%umass.bitnet@wiscvm.wisc.edu UUCP: ...seismo!UMASS.BITNET!mkrieg But don't let that stop you, USMail: Hampshire College, Amherst, MA 01002 happiness is subjective. Phone: (413) 549-5113 <odd hours, but try!> `-----------------------------------------------'