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You're talking about two different things: eliminating hardware by doing more in software (what the article was stating) vs consolidating discrete logic to an A
by blihp 5y ago
You're talking about two different things: eliminating hardware by doing more in software (what the article was stating) vs consolidating discrete logic to an ASIC (both the IWM and the discrete logic it replaced performed the same task in hardware. The IWM just reduced it to one chip allowing them to eliminate the controller PCB)
- T-A 5y ago> The IWM just reduced it to one chip allowing them to eliminate the controller PCB) From the Wikipedia article: "The floppy drive controller was built with 8 ICs, one of which is the PROM, containing tables for the encoder and decoder, the state machine, and some code." (My emphasis.) What made it at all possible was moving most of the logic to the CPU: https://retrocomputing.stackexchange.com/a/7188 https://retrocomputing.stackexchange.com/a/7188 The IWM chip, used in the prototype Mac with double sided "Twiggy" drives, and later in the original production Mac 128k with Sony 3.5" diskette drives, is basically Woz's original disk controller design (converted by Wendell Sander and Bob Bailey to NMOS), with the addition of buffer registers to allow the processor to run a bit more asynchronously. But, except for not having to run (* almost) synchronous with the disk data rate, the 68k CPU did all the raw data decoding (GCR nibbles to bytes, etc.) and head stepping in software, very similar to the 6502 code in the Apple II (DOS) RWTS.
- rasz 5y agoNo, IWM replaced floppy controller ASIC integrating pll, track and sector ID detectors, bit shifter, FM/MFM decoders/encoders, and CRC logic. All of this was replaced by simple bit shifter, state machine and software running on main CPU of the computer. Amiga employed similar trick reusing Blitter to encode/decode tracks.