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Weird Macintosh '512K'
Posted by: ibook99 on 2022-11-10 20:29:15 I recently purchased my first Compact Mac, it has the Macintosh 512k badge on the back; however, when I looked at the serial number, I was very confused. It appears to have been made on the 3rd week of 1984. I decided to open it, and it looks like there was some modification done to the logic board in 1986. My theory is that it was originally a 128k, and it was upgraded. For some unknown reason, they put a 512k back on it, which is odd. I have provided pictures, does this look like a 128k board that may have been made in the 3rd week of 1984? I have yet to find a Macintosh made before the 3rd week of 1984.
Posted by: ArmorAlley on 2022-11-10 22:41:38 The obvious question is: how much RAM does it have? 128KB? 512KB? Some other multiple of 64K?
Posted by: bibilit on 2022-11-10 23:23:56 This is an original Macintosh 128 board upgraded to 512k. i can clearly see the new ram chips and the logic one for decoding. Moreover the board only says Macintosh, not like the late version with both 128 and 512k labels.
Posted by: ibook99 on 2022-11-11 05:23:36 When I boot it up, I will have to see how much ram it has. I just noticed that it is Samsung branded ram since that is the 1980s Samsung logo. Each chip says KM41256-12. When I Google search it, it comes up as Samsung 256K Ram. Is it possible for this computer to have a total of 4MB of ram (there are 16 of these 256K chips)? I am a real newbie when it comes to Macs of this vintage.
Posted by: cheesestraws on 2022-11-11 05:45:09 Samsung 256K Ram That'll be 256kbit, not kbyte. It can be confusing when they abbreviate it to 'K', but generally the individual chips are measured in bits rather than in bytes.
Posted by: dochilli on 2022-11-11 07:06:53 256 kbit/ 8 =32 kilobyte. Each chip has 32kb of ram. 16x32=512kb. You have 512kb ram.
Posted by: bibilit on 2022-11-11 07:34:15 You can leave the board that way, or just remove The piggybacked 74LS253, extra wires and redo a small trace cut on the underside of the board to go back to 128k
Posted by: unity on 2022-11-11 07:39:33 Moreover the board only says Macintosh, not like the late version with both 128 and 512k labels. ? Not sure what you mean by that. Both the 128k and 512k boards say Macintosh on them. Has the FCC label also been changed? Usually an upgrade kit comes with a badge and new regulations label. The odd thing here is that this was a modification, not an official Apple upgrade kit. So the badge could have been replaced by the user or shop that did the modification. No way to know for sure. Its also possible the shop did it all and charged the customer for a 512k upgrade but simply modified the board, would have likely been far cheaper - but if a shady shop, charged the customer the full Apple upgrade price and kept the new 512k board to resell.
Posted by: bibilit on 2022-11-11 08:03:44 The first board has no information for ram size, just Macintosh, while the second one still says Macintosh but also two labels with a ticking mark for 128/512.
Posted by: olePigeon on 2022-11-14 10:20:19 I'd say just leave it. There's no question it's an original 128k. It's a period appropriate modification, and now it has a very useable 512k to work with. 🙂
Posted by: unity on 2022-11-14 14:58:16 Ah... I see what you ya mean. I thought you were saying "Macintosh" was removed from the screening.
Posted by: JC8080 on 2022-11-20 06:48:34 I'd say just leave it. There's no question it's an original 128k. It's a period appropriate modification, and now it has a very useable 512k to work with. 🙂 This is good advice, as much as people want a totally stock 128k, there is something to be said for a period correct mod like this. It's a small time-capsule, it shows that someone actually used that machine back in the day and invested in it to bring it up to a more useable spec.
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