A retro computing enthusiast has successfully shoehorned 4MB of RAM into an Apple Macintosh Classic computer without using a daughterboard. Normally, this isn’t possible, but Adrian Black of Adrian’s Digital Basement compared the similar Motorola 68000 CPU-packing Mac Classic and SE models, and the inspired hardware hacking session paid off.
Black explains that he had a leftover Mac Classic motherboard with some chips missing after a repair session. He wanted to upgrade this from its standard onboard 1MB of RAM to an expansive 4MB. However, Mac Classics normally require the use of a RAM-packing daughterboard to accomplish such an upgrade.
After pondering over the schematics of the Mac Classic and the similar Mac SE, Black noticed that the latter could accept 4MB added to the motherboard via four SIMM slots — no daughterboard required. The Macintosh Classic schematics revealed it basically uses “a Macintosh SE motherboard — shrunk down.” That meant he could probably hack the Classic to 4MB onboard without ordering and waiting for a daughterboard.
A combination of convenience and inquisitiveness, rather than necessity, was the mother of invention here, but it still makes for a captivating video. Before he gets on with the modding process, Black admits that replacement daughterboards that can expand a Mac Classic to 4MB are quite easy to get and cost only $30 or $40. Thus, he notes, the mod is “probably kinda pointless,” except in the rare case that one of the two support chips is damaged, as those UL1 CAS PAL chips are harder to acquire.
The hardware hacking part of the video shows two redundant chips removed from the motherboard, along with a couple of other minor component changes, before swapping out the RAM chips that are already present on the Mac Classic motherboard. Specifically, the eight ‘44256 RAM chips’ are replaced by four ‘4400 RAM chips’ taken from a common 4MB 72-pin SIMM. Later, some wires had to be run and a couple of resistors were inserted to get the new RAM configuration to work and echo the Mac SE RAM subsystem design.
The first boot after the mod almost worked but ended with the ‘sad Mac’ error code. Black initially thought the error code pointed to a RAM issue, but some other ancient Mac tinkerers told him it was a non-volatile RAM settings issue. Those earlier suspicions turned out to be correct, though, as the schematics led him to switch around some of the bodge wires with a successful boot to the ‘Mac OS missing’ screen.
Black wraps up the video by successfully running the system through the Speedometer test suite, which would usually fail if any of the components had issues. And now, 40 years or so later, this Mac Classic how has quadruple the onboard memory.
