scotty@l5comp.UUCP (Scott Turner) (05/22/87)
Since Apple just doubled the clock rate available to the disk section of the new Macs, with the stated purpose of being ready for the new 1.4 meg drives, it would seem most likely that the doubling in storage capacity is coming from a higher data rate rather then twice as many tracks. On the "it can't be done" front. I received a phone call last night from one of the groups working on reading mac disks on the Amiga. They claim they can read 4/5ths of the Mac disk with VERY LITTLE TROUBLE. Reading the last 1/5th does present some what more of a challenge but they claim they can handle it. The greatest obstacle still left is how to calculate the 24 bit CRC used on the Mac disks. No dox have been found at present describing the polynomial used. Can anyone out there help? Drop me an E-Mail and I'll pass the info along. [So much for "FOG" :)] Scott Turner -- L5 Computing, the home of Merlin, Arthur, Excalibur and the CRAM. GEnie: JST | UUCP: stride!l5comp!scotty | 12311 Maplewood Ave; Edmonds WA 98020 If Motorola had wanted us to use BPTR's they'd have built in shifts on A regs [ BCPL? Just say *NO*! ] (I don't smoke, send flames to /dev/null)
farren@hoptoad.uucp (Mike Farren) (05/23/87)
In article <138@l5comp.UUCP> scotty@l5comp.UUCP (Scott Turner) writes: >On the "it can't be done" front. I received a phone call last night from one >of the groups working on reading mac disks on the Amiga. They claim they can >read 4/5ths of the Mac disk with VERY LITTLE TROUBLE. Reading the last 1/5th >does present some what more of a challenge but they claim they can handle it. All right, all right, I give. I still have grave doubts about this stuff, but if they can do it, it must be possible, mustn't it? Sheesh, the things my mouth (fingers?) can get me into sometimes. I hereby apologize for my adamant defense of the "impossible" stance, and for an extremely offensive flame directed to Scott. HOWEVER: >[So much for "FOG" :)] The other point in my original posting was extremely badly (and baldly) stated, and buried in a bunch of "they can't do that" verbiage which allowed the point to be ignored in the general flamage (mostly justified, I must admit) which followed. That point, which I believe led to the "FOG" comment above, was simply this: when anyone is discussing the capabilities of the Amiga, it is extremely important to distinguish between real capabilities and "tricks", and to state the difference clearly. The example is the original posting by Scott Turner, in which he strongly implied that the Amiga hardware included provisions to control disk drive speed, and baldly stated that the disk controller hardware had provisions to change data timing at will. Within the context of the discussion his statements appeared in, both of these statements were untrue. Controlling disk drive speed by pulsing the motor control line does, in fact, change the drive speed. This is not, however, a built-in capability of the machine, but a software kludge - imaginative, but a kludge nonetheless, highly dependent on the physical construction of the drive mechanism, and absolutely NOT gauranteed to be constant from drive to drive. Secondly, the matter of disk data timing. Although the ADKCON register has a bit, FAST, which will change bit-cell timing from 2 microseconds to 4, this is not "control of disk data timing" in the sense in which it was being discussed at the time, which was basically a discussion of smoothly varying data timing over a given range, not switching between two discrete values. My problem with this was, and still is, that someone not intimately familiar with the way the Amiga hardware REALLY works could easily get very confused, and waste a lot of time trying to figure out how to get these capabilities from a machine which doesn't possess them. We all have much better things to do than to track down non-existent "facts". Scott has proven, several times over, that he does, indeed, understand the Amiga extremely well. My complaint was that he unintentionally made some VERY misleading statements. My mistake was to respond in a very extreme manner to what was a small offense. My apologies, again, for badly overstating the case, but I don't believe that my real point, as stated in the last three paragraphs, was any less valid for that. (BTW, as someone with 15 years of experience in this field, including the design of many disk controllers and disk device drivers, I am quite impressed with the people at Central Point if they really do manage to pull off the Mac-to-Amiga trick. I would have sworn (hell, I DID swear) that it was impossible. Must be getting old (sigh).) -- ---------------- "... if the church put in half the time on covetousness Mike Farren that it does on lust, this would be a better world ..." hoptoad!farren Garrison Keillor, "Lake Wobegon Days"