PowerBook 1xx Upgrade Questions

[akator70]

I've done a bit of searching, and while my Google-fu is usually pretty good I haven't been able to come up with any answers to these questions.

Are the PowerBooks in the 100 series limited to a max of 8 or 14MB because of a hardware limitation? I ask this because many Macs were limited to the maximum memory possible at the time but when larger chips became available those Macs could take advantage of them. If this isn't a hardware limitation, it seems theoretically possible to create or mod a memory board with compatible larger memory. (This has been with other classic computers.)

Were there any CPU board upgrades? I know there were upgrades available for the 500 series and later PowerBooks, but I haven't been able to find any info for the 100 series. There have been some interesting modern upgrades for other classic computers, especially the Amigas. Since the Amigas shared the 68K processing family, there's already some solid starting points for doing similar with Macs.

 

[3lectr1cPPC]

Pretty sure RAM was a hardware thing, but not 100% on that.

CPU wise, no upgrades were made, likely because a lot more than just the CPU was on the CPU board on the 100 series laptops. Like, a LOT more.

 

[twelvetone12]

Well on the pb100 at least the CPU board is super simple, there is just the 68000 and two ROM chips. I'm not sure why no upgrades were made, maybe the speed gain is marginal and nobody bothered.

 

[Phipli]

The PB100 is very different to the other Powerbook 1xx macines.

The PB100 doesn't have a memory manager, and the 68000 only has a 16MB address space including RAM, ROM and hardware addresses.

You'll be stuck with whatever apple says on that machine.

I've looked at the PB145 a little and you could add more RAM, but you'd need to write some software that did what compact virtual did to use it. This is because the OS expects a continuous address range of RAM, and the next free address range in the 145 isn't next to RAM.

I don't have those kind of programming skills.

 

[twelvetone12]

Well I would imagine that something like the Performer SE accelerator that uses system ram would be possible to build, I'm not sure it's worth it.

 

[twelvetone12]

So just out of curiosity I grabbed the schematic of Bolle's replica of the Performer SE accelerator, which sits on the SE PDS or directly replacing the CPU in the Plus or Classic, which is basically what is in the PB100 daughter board. I guess it could work? All the data and address signals are the same, one would need to cram there the GALs and the mac roms. Somewhere on this site there was an user doing the same for the Portable, but I think it never got anywhere. I wonder how the performance would be between a 16Mhz '00 and '30?

 

[avadondragon]

I have wondered the same sort of questions. The only source I could find to shed some light on those secrets were the Apple developer notes which can be found here: https://powerbook.micahgartman.com/ if you want to take a look.

It has been quite a while since I looked at the dev notes myself but I believe my assessment was that there is an inherent hardware limitation. It could be overcome but it looks much harder than I'd be willing to try to tackle.

I had a few programs that needed a tiny bit more RAM to really be useable on the PB1xx series.

 

[beachycove]

I am no expert in the PB1xx series, so correct me if I am wrong, but isn’t it possible to swap the processor card from, say, a 160 into a 140 and thus get a speed bump?

 

[demik]

Upgrades were difficult because there is no real "processor board"

You can swap the "processor board" between compatible generations, ex 140/170 or 145/160/180. Since the video chip is on the CPU board, "c" CPU boards (165c/180c) are interchangeable but do require a color screen

The RAM limitations are due to the memory controller. This is explained in the developer notes.

Keep in mind theses CPU have relatively weird board combinaisons, one main logic board, plus one CPU board with some RAM and the video card in it, and even more weird ones like the colors models having the ROM and the integrated RAM on a third board (not counting the jedi board who does have the speaker amp, pram battery and some video control circuity)

 

[3lectr1cPPC]

140/145/170 have the same motherboard so can all CPU card swap. 145 doesn't use the 160/180 main board.

 

[akator70]

I read through the developer notes for both the 165c and the 160/180 because the second is refereed to by the first. The 160/180 DN says:

Like the PowerBook 140/145/170, the PowerBook 160 and PowerBook 180 always operate in 32-bit addressing mode. To maintain compatibility with software that uses 24-bit addressing conventions, the memory management unit (MMU) in the 68030 is used to map 24-bit addresses to their 32-bit equivalent.

In 32-bit mode, the 68030 supports a 4 GB address space. In 24-bit mode, however, the upper 8 address bits are ignored, and the maximum address space is limited to 16 MB. The MMU remaps addresses so that RAM, ROM, VRAM, and I/O all appear within this 16 MB range. Although the address translation is transparent to software, it has the effect of limiting the amount of addressable RAM to 8 MB.

So if I understand this correctly, the MMU is the limiting factor? Do these PowerBooks have a different MMU than other 68030 Macs?

 

[akator70]

It doesn't really make any sense that the 68030 MMU limits the RAM to 16MB since there are so many other 68030 Macs that can use far, far more than 16MB. I remember having 17MB in a IIsi I owned back in 1991. I suspect it's something in the PowerBook ROMs that restrict the MMU to 16MB.

While this isn't a particularly important issue, it does make me curious if a customized ROM could remove this restriction. Of course, that's pointless without larger memory upgrade options, but that is theoretically resolvable as well.

 

[avadondragon]

The MMU is the same as the one found in other 68030 machines so it isn't a limiting factor. If you look at how they've set up the memory map on these machines there is actually a huge block labeled "Expansion RAM" (could easily accommodate 128MB in that address space) which could presumably be used somehow if you can figure out how to get the MMU to point there. There is a slight inconvenience in that it is non-contiguous with the default RAM area.

Now it has been quite a while so I wouldn't swear to the accuracy of my memory but I think the schematics showed that there just weren't enough address lines going to the RAM expansion port to support beyond the stated maximum limits. You could potentially make a custom and very messy RAM expansion board with loads of bodge wires to support the needed address lines I suppose.

Then there's the fact that these machine use fairly uncommon PSRAM which is bulky and hard to source. It would be difficult to physically cram a substantial amount of RAM into the machine given the limitations of the available chips of that type. Others might know more than I about possible alternatives. I'm just not aware of any newer, higher density, chips that might be compatible.

Probably possible but it would be very very difficult. Which is such a shame. I'd love to have 128MB of RAM available on my PB180c while running NetBSD. It might actually be somewhat usable then!

 

[akator70]

^ Thanks for the info. This explanation makes sense, unlike what was in the developer notes. It also explains what seems like an arbitrary memory limitation considered the 68030 (and MMU) doesn't have those same limitations.

 

[matcox]

Upgrades were difficult because there is no real "processor board"

You can swap the "processor board" between compatible generations, ex 140/170 or 145/160/180. Since the video chip is on the CPU board, "c" CPU boards (165c/180c) are interchangeable but do require a color screen

The RAM limitations are due to the memory controller. This is explained in the developer notes.

Keep in mind theses CPU have relatively weird board combinaisons, one main logic board, plus one CPU board with some RAM and the video card in it, and even more weird ones like the colors models having the ROM and the integrated RAM on a third board (not counting the jedi board who does have the speaker amp, pram battery and some video control circuity)

Anyone ever tried using a 165c daughtercard in a 180c. I had tried this a while back and it DID NOT work. Although they look the same there must be some studdle differences perhaps the rom on it? OR maybe there was something else going on with my config.... I assumed the pinout was different.