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LC 475, I don't know what I'm looking at
Posted by: TheGoneJackal on 2025-06-23 19:11:04 Thanks for everyone's expertise, as I'm very new to 68k macs. I'm looking over other examples of 475's which don't have what I've highlighted. In between the two VRAM slots and the single RAM slot, is another slot. What is that slot and what can I put there? The computer runs fine without anything in it. Your help would be appreciated!
Posted by: mikes-macs on 2025-06-23 19:38:16 That looks like a ROM slot. You have ROMs already soldiered on the LB but that board can deactivate them and use a ROM SIMM
Posted by: killvore on 2025-06-23 22:13:20 Congratulations on your machine! The LC475 is fantastic 😄 great form factor to work on, and thanks to some R&D by members of this forum you can overclock it in software: https://68kmla.org/bb/index.php?thr...605-without-soldering-or-spicy-o-clock.47946/
Posted by: zigzagjoe on 2025-06-23 22:27:21 It is a ROM slot, but keep in mind that only a small subset of Mac ROMs will correctly disable the built-in ROMs in Quadras. To my knowledge only Caymac's ROMs and my ISP-SIMMs properly handle that, any other ROM shouldn't be used.
Posted by: cheesestraws on 2025-06-24 00:20:56 It's also not actually very useful to replace the ROM. A lot of people seem to like doing it, but there's not objectively a huge amount of reason. The reason it was there was presumably so that if they found bugs after the first few batches of machines were in the field (or even in late production) they wouldn't have to take them all back and desolder the ROMs to fix it. Once it had demonstrated itself stable, I suspect the ROM slot was quietly dropped.
Posted by: joshc on 2025-06-24 03:15:10 I am pretty sure my 475 board does not have the ROM slot populated, but the PCB footprint is still there for it. So they will have got to a point in production where they stopped populating them. As cheesestraws says, there is little benefit in actually using a custom ROM most of the time.
Posted by: TheGoneJackal on 2025-06-24 06:15:40 Thanks everyone for your knowledge! From scouring these forums are the following deductions accurate? I'm getting the sense that putting a ROM SIMM in would allow me to bypass a memory check that would otherwise make my startup process fairly long. Especially if I buy more RAM, as I just happened to see a 128 mb module on ebay. It's not that I need that much, but just hypothetically, putting that much RAM in will likely make my startup process that much longer? zigzagjoe, although it's unavailable from Caymac's shop, is your Das BlinkenKombo the only ROM SIMM that will physically fit inside an LC 475 with the case closed? Cheesestraws and joshc, thanks for your opinions. I'm looking at the BMOW SIMM and apart from the memory check, it looks like you can boot into the ROM and utilize the flashed tools on it, for diagnostic/utility purposes should you ever need to. Which I'm getting the sense... does not happen very often, so why bother? Are there any other reasons why someone would want to put in one of these custom ROM SIMMS?
Posted by: mikes-macs on 2025-06-24 06:53:40 Even with 128mb of memory the test on that Mac won’t take long. There may be other ways to disable the test without needing a new ROM.
Posted by: cheesestraws on 2025-06-24 07:29:09 bypass a memory check that would otherwise make my startup process fairly long Given that most memory one can get these days is old and from dubious sources, I'm always surprised how keen everyone is to disable their memory tests. They must like troubleshooting weird issues much more than I do. Which I'm getting the sense... does not happen very often, so why bother? Yes; I mean it's cool that you can do that, but I think its actual usefulness is rather overstated.
Posted by: zigzagjoe on 2025-06-24 07:56:06 Thanks everyone for your knowledge! From scouring these forums are the following deductions accurate? I'm getting the sense that putting a ROM SIMM in would allow me to bypass a memory check that would otherwise make my startup process fairly long. Especially if I buy more RAM, as I just happened to see a 128 mb module on ebay. It's not that I need that much, but just hypothetically, putting that much RAM in will likely make my startup process that much longer? zigzagjoe, although it's unavailable from Caymac's shop, is your Das BlinkenKombo the only ROM SIMM that will physically fit inside an LC 475 with the case closed? Cheesestraws and joshc, thanks for your opinions. I'm looking at the BMOW SIMM and apart from the memory check, it looks like you can boot into the ROM and utilize the flashed tools on it, for diagnostic/utility purposes should you ever need to. Which I'm getting the sense... does not happen very often, so why bother? Are there any other reasons why someone would want to put in one of these custom ROM SIMMS? I believe the blinkenkombo is the only one that is slightly short for LC475. That said, I know the ISP-SIMM also works in the Q605 case, but I think it is taller than the 475 case. I am of the school of thought that I don't see a point in romdisk / modified boot chimes / disabled RAM checks. With the general tetchiness of old computers I welcome the additional sanity check. Personally I use the ROM slot for bare-metal programming, but that's something of an unusual case 🙂
Posted by: killvore on 2025-06-24 08:19:26 I'd suggest 32MB - this gets you 36MB with the soldered 4MB, plenty for a 68k machine, very reasonable boot times, and no potential issues closing the lid 😄 (some of those higher capacity RAM chips are longer and can get in the way of getting the lid on)
Posted by: joshc on 2025-06-24 08:20:07 The irony here is wanting to use an old, slow computer and then not being patient enough to wait a minute for a ram check 😀
Posted by: killvore on 2025-06-24 08:30:53 That's the thing, though - they don't FEEL slow (at least with System 7.1) - unless you're doing something crazy like opening a jpeg 😆
Posted by: Powerbase on 2025-06-24 08:34:08 The irony here is wanting to use an old, slow computer and then not being patient enough to wait a minute for a ram check 😀 To be honest, with a SDtoSCSI device, the 475 boots fairly quick. The memory test (at least with maxed ram in mine) is an entire minute of wondering if its testing the ram or simply not booting. The RAM test is nice but honestly kind of useless after the first time. I don't remember RAM going bad a lot back in the day, like ever going bad. The ONLY time I've had RAM suddenly 'not work' was about 2 years ago in my PC.
Posted by: cheesestraws on 2025-06-24 08:54:00 The RAM test is nice but honestly kind of useless after the first time. I don't remember RAM going bad a lot back in the day, like ever going bad. You have been lucky then. RAM definitely goes bad, and increasingly so as it gets older.
Posted by: joshc on 2025-06-24 09:04:37 The RAM test is nice but honestly kind of useless after the first time. Isn't this like saying, a car shouldn't have self-diagnostics and inform of you when things break, because they aren't broken now? RAM can fail at any time...
Posted by: Powerbase on 2025-06-24 10:06:55 Isn't this like saying, a car shouldn't have self-diagnostics and inform of you when things break, because they aren't broken now? RAM can fail at any time... RAM can fail, yes, but a mandatory test every startup isn't necessary. It doesnt fail at that frequency. Thats like having to wait five minutes every time you start your car while it does diagnostics just because there's a possibility it might have a problem at some point. The main point, being, that you should be able to disable it in software like every other Mac (that I know of from that time).
Posted by: mikes-macs on 2025-06-24 11:53:50 So, it’s a ROM slot.
Posted by: Powerbase on 2025-06-24 12:02:18 So, it’s a ROM slot. Long story short... yes.
Posted by: joshc on 2025-06-24 12:50:49 Speaking of ROMs...... from https://folklore.org/Busy_Being_Born,_Part_2.html
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