Rewritable ROM For The Mac Plus

The Macintosh Classic – a small all-in-one computer with a 9″ monochrome screen –  was one of the more interesting machines ever released by Apple. It was the company’s first venture into a cost-reduced computer, and the first Macintosh to sell for less than $1000. Released in 1990, its list of features were nearly identical to the Macintosh Plus, released four years earlier. The Classic also had an interesting feature not found in any other Mac. It could boot a full OS, in this case System 6.0.3, by holding down a series of keys during boot. This made it an exceptional diskless workstation. It was cheap, and all you really needed was a word processor or spreadsheet program on a 1.44 MB floppy to do real work.

[Steve] over at Big Mess O’ Wires had the same idea as the Apple engineers back in the late 80s. Take a Macintosh Plus, give it a bit more ROM, and put an OS in there. [Steve] is going a bit farther than those Apple engineers could have dreamed. He’s built a rewritable ROM disk for the Mac Plus, turning this ancient computer into a completely configurable diskless workstation.

The build replaces the two stock ROM chips with an adapter board filled with 29F040B Flash chips. They’re exactly what you would expect – huge, old PDIPs loaded up with Flash instead of the slightly more difficult to reprogram EEPROM. Because of the additional space, two additional wires needed to connected to the CPU.  The result is a full Megabyte of Flash available to the Macintosh at boot, in a computer where the normal removable disk drive capacity was only 800kB.

The hardware adapter for stuffing these flash chips inside a Mac Plus was made by [Rob Braun], while the software part of this build came from [Rob] and [Doug Brown]. They studied how the Macintosh Classic’s ROM disk driver worked, and [Rob Braun] developed a stand-alone ROM disk driver with a new pirate-themed startup icon. [Steve] then dug in and created an old-school Mac app in Metrowerks Codewarrior to write new values to the ROM. Anything from Shufflepuck to Glider, to a copy of System 7.1  can be placed on this ROM disk.

This isn’t the first time we’ve seen ROM boot disks for old Macs. There was a lot of spare address space floating around in the old Mac II-series computers, and [Doug Brown] found a good use for it. Some of these old computers had optional ROM SIMM. You can put up to 8 Megabytes  in the address space reserved for the ROM, and using a similar ROM disk driver, [Doug] can put an entire system in ROM, or make the startup chime exceptionally long.

10 thoughts on “Rewritable ROM For The Mac Plus

    1. Not at all, the Mac mini was the modern answer to the Mac Classic line, an affordable, tiny Mac that wasn’t the most powerful but was nonetheless useful and practical. I do wish they had really brought the Mac Classic line back in the form of a smaller, cheaper LCD iMac, but the Mac mini was a good machine in its own right.

    2. I’ll tell you how this started. Steve Jobs wanted to release the first Mac for under $2k. Unfortunately he had hired John Sculley from Pepsi, who priced it at $2500 to get higher profit margins. (This pissed off the Mac engineers, as you can imagine.) This “overpricing” continued through the 90s, sometimes to excess (the $9000 20th Anniversary Mac) and saddled the company with the reputation of excessively overpriced products. Once Jobs returned, though, prices (IMHO) fell back in line to “normal” levels. (More expensive than PC OEMs for obvious reasons: internal dev teams don’t work for free.)

      1. > sometimes to excess (the $9000 20th Anniversary Mac)

        It was closer to $10k when it was first released, however that meant a freakin’ limo would deliver it to your house, and a guy in a tux would set it up. This was later reduced to ~$2000, sans limo, when ordered online after Jobs came back. You can’t point to the TAM as being overpriced. It was, after all, a status symbol.

        But yeah, overall, Apple products are always more expensive than their PC counterparts. Whether that’s do do with profit margins (50% in the case of the original Macintosh, continuing up until the Classic and beyond), the fact that you’re basically building a new implementation for each new design (look at the 6400 series. It’s fucked up, circuit-wise), or the fact that you’re competing against OEMs is another question entirely.

        1. I paid approx $1000 for a Mac 512K at the campus computer store

          “you’re basically building a new implementation for each new design ”

          HUH? The Apple floppy controller is pretty much the same from the original Apple II all the way into the second or third generation of Macs. The Z8530 serial port chip stayed the same throughout the 68K Macs.

          ” the fact that you’re competing against OEMs”

          Oh you mean companies like Dell and HP and IBM that have been farming out their manufacturing for decades?

          The simple fact of the matter is that people pay more for quality. Maybe you don’t see “quality” in a serious lack of need for technical support because it doesn’t show up in the BOM but for people with creative talents, the no-muss-no-fuss plug-and-play aspect of the Mac meant that visual artists and musicians did not have to become DOS weenies and learn about IRQs to get their systems up and running. Again if you can’t see the value of this, you’re just refusing to look.

  1. retro mac articles bring the retro mac haters out into the sunshine, they can dust off their arguments from 1992 all over again, but let’s remember that your local bank’s checking account offers a higher return than Microsoft stock.

  2. Pretty ironic that they used a 1984 reference in their commercial – breaking users out of the control but these days they are controlling the way their developers make apps, hardware products (DRM) etc.

    Don’t expect the i-products to be anything but life style products. So that’s why when they make “cheaper” iphones for the Asian market, they don’t sell as well as they thought it would be. People buy it for status symbol to show they can (pretend to) afford luxury goods.

  3. Vintage Mac is awesome. Thanks to everyone that helps support our community!
    Mike from Australia and his SCSI2SD, Steve with his Floppy Emu/ HD20 Emu, Plus Rom Hacks, IIx,IIfx,IIcx,IIci,IIsi,SE/30 (2mb and 8mb) Programable Rom Simm hacks from Dougg3 and S/W by bbraun. jt for all his mac hack knowledge (IIsi radius pivot video card in the SE/30) Techknight with a 7/8mb ram expansion card for the Mac Portable, Max for his hand made active terminated SCA to SCSI adapters. gnolivos for his 3D printed floppy gear replacements for the auto-eject assm. And many others from Over Clocking to new Pram Battery adaptor boards.

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