Does the Mac II need FDHD kit for +8MB?

[reodraca]

I'm installing the 68851, so I'm wondering if that's enough for more than 8 MB. Does it also require the FDHD kit?

 

[Arbee]

The FDHD ROMs are required for RAM sizing to work properly above 8 MB. You don't need the actual SWIM floppy controller and SuperDrive.

 

[Trash80toHP_Mini]

Just need to use MODE32 to overcome the 8MB limit, no?

 

[Arbee]

The pre-FDHD ROMs for the Mac II will fail if they see more than 8 MB of RAM. MODE32 can only help you if the system can boot in the first place.

 

[chip-64bit]

The pre-FDHD ROMs for the Mac II will fail if they see more than 8 MB of RAM. MODE32 can only help you if the system can boot in the first place.

Hi, I was wondering if the Mac II can run without the FPU. Thanks!

 

[Mk.558]

Macintosh II
============
There are currently four SIMM sizes for the Macintosh II:
* 512 KB
* 1 MB
* 4 MB
* 16 MB
The Macintosh II requires special 4MB SIMMs. Be sure to specify your Macintosh model when ordering these SIMMs and ensure that the
vendor is aware of the difference. The Macintosh II requires the SuperDrive (FDHD) Upgrade to use 4MB or 16MB SIMMs.
To take advantage of more than 8MB of physical RAM, the Macintosh II MUST have a PMMU installed, so that MODE32 can expand the
system's memory map.
With the original ROMs, the Macintosh II will not start up if you install 4MB or 16MB SIMMs in bank A. You'll hear musical chimes at startup,
indicating a hardware failure. Install 4MB SIMMs in bank B, and use 256K or 1MB SIMMs in bank A. This provides a maximum of 68MB of
RAM installed.
With the FDHD ROMs installed, up to 16 MB SIMMs are supported in bank A increasing the maximum memory configuration to 128 MB.
Restrictions on placing SIMMs in the Macintosh II are similar to those for the Macintosh Plus and Macintosh SE: the SIMM sockets are divided
into two banks, A and B, each containing four SIMM sockets. All SIMMs in either bank must be of the same type. No resistors need to be cut to
differentiate between the possible configurations.
With original ROMs:
Bank A 256K to a Maximum 1 MB
Bank B empty 16 MB
-----------------------
Total Memory 1 MB 68 MB
With FDHD ROMs:
Bank A 256K to a Maximum 16 MB
Bank B empty 16 MB
-----------------------
Total Memory 1 MB 128 MB
SIMM Speed Ratings
==================
* Macintosh Plus: SIMMs must be rated 150ns or faster (the number on the SIMM must be 150 or smaller)
* Macintosh SE: SIMMs must be rated 150ns or faster (the number on the SIMM must be 150 or smaller)
* Macintosh II: SIMMs must be rated 120ns or faster (the number on the SIMM must be 120 or smaller)

As for the FPU, you should be able to run it just fine without the FPU. Only certain programs used the FPU, see here. Most people will never need the FPU.

 

[willmurray461]

The pre-FDHD ROMs for the Mac II will fail if they see more than 8 MB of RAM. MODE32 can only help you if the system can boot in the first place.

I don't think this is correct.

According to the one of the reproduction Mac II 4MB PAL SIMM designers, a Mac II with stock ROM and 68851 can support up to 68MB of RAM. The original Mac II ROMs require that bank A is populated with 256KB or 1MB SIMMs, but Bank B can use 256KB, 1MB, 4MB or 16MB SIMMs. The FDHD upgrade kit (which includes IIx ROMs) allows the computer to use 4MB or 16MB SIMMs in any bank, for a maximum of 128MB.

I'm guessing you got your information from the Mac II page on everymac.com, which says that a stock Mac II can address 8MB, a Mac II w/ IIx ROMs can address 68MB, and a Mac II with IIx ROMs and MODE32 can address 128MB. However, this doesn't make sence, since a Mac without MODE32 wouldn't be able to use 68MB (it would still only be able to use 8MB).

@reodraca, if you are trying to install SIMMs larger than 1MB in a Mac II or IIx, know that standard 30-pin SIMMs won't work. You need special "PAL SIMMs" that have additional circuitry to accomodate a quirk of the Mac II's memory refresh circuitry.

 

[Arbee]

For what it's worth, my information is from disassembling the ROM code to figure out "safe" memory size settings for MAME. The system heap was consistently malformed during startup when there was more than 8 MB of RAM with the original ROMs. The IIx/FDHD ROMs worked as advertised. So if I had a II with original ROMs I wouldn't use it for any work you can't stand to lose if it has more than 8MB.

Also, in a non-MODE32 situation Finder will still show the correct amount up to 128MB, apps just won't be able to use it.

 

[croissantking]

As for the FPU, you should be able to run it just fine without the FPU. Only certain programs used the FPU, see here. Most people will never need the FPU.

If you remove the FPU on an SE/30, it will crash shortly after booting, often with an F-Line error. So I wouldn’t assume the Mac II would work fine without one, as the system software might expect it to be there.

 

[Mk.558]

Fair, since the IIx and the SE/30 are basically identical in terms of system design and ROM.

I wonder what kind of FPU calls are happening at system boot time?

 

[willmurray461]

For what it's worth, my information is from disassembling the ROM code to figure out "safe" memory size settings for MAME. The system heap was consistently malformed during startup when there was more than 8 MB of RAM with the original ROMs. The IIx/FDHD ROMs worked as advertised. So if I had a II with original ROMs I wouldn't use it for any work you can't stand to lose if it has more than 8MB.

Also, in a non-MODE32 situation Finder will still show the correct amount up to 128MB, apps just won't be able to use it.

I'm not sure how MAME emulates the Mac II, but is it possible what you experienced was related to the Mac II's ROMs not supporting >1MB SIMMs in bank A?

I found another source here which again claims that stock Mac II ROMs support up to 68MB with a PMMU, so I'm pretty confident it's the case.

Also, yes a non-MODE32 system will recognize RAM over 8MB without letting you use it, but I don't think that's what the authors at everymac meant.

 

[David Cook]

I'm not sure how MAME emulates the Mac II, but is it possible what you experienced was related to the Mac II's ROMs not supporting >1MB SIMMs in bank A?

I found another source here which again claims that stock Mac II ROMs support up to 68MB with a PMMU, so I'm pretty confident it's the case.

Also, yes a non-MODE32 system will recognize RAM over 8MB without letting you use it, but I don't think that's what the authors at everymac meant.

I rely on https://wiki.preterhuman.net/Macintosh_II for the memory table towards the end of the page. It lists all the configurations and whether a PMMU or FDHD ROM are needed. I have several Mac II computers without FDHD ROMs and I can confirm getting them to work with more than 8MB of memory. However, I have not stress tested them, so I cannot say for certain whether the System heap is corrupt.

 

[reodraca]

I installed the 68851 and put MODE32 on the system for the hell of it, even though the system had what I assumed was 8 MB. Turns out it has 20. It seems stable.

 

[reodraca]

I don't think this is correct.

According to the one of the reproduction Mac II 4MB PAL SIMM designers, a Mac II with stock ROM and 68851 can support up to 68MB of RAM. The original Mac II ROMs require that bank A is populated with 256KB or 1MB SIMMs, but Bank B can use 256KB, 1MB, 4MB or 16MB SIMMs. The FDHD upgrade kit (which includes IIx ROMs) allows the computer to use 4MB or 16MB SIMMs in any bank, for a maximum of 128MB.

I'm guessing you got your information from the Mac II page on everymac.com, which says that a stock Mac II can address 8MB, a Mac II w/ IIx ROMs can address 68MB, and a Mac II with IIx ROMs and MODE32 can address 128MB. However, this doesn't make sence, since a Mac without MODE32 wouldn't be able to use 68MB (it would still only be able to use 8MB).

@reodraca, if you are trying to install SIMMs larger than 1MB in a Mac II or IIx, know that standard 30-pin SIMMs won't work. You need special "PAL SIMMs" that have additional circuitry to accomodate a quirk of the Mac II's memory refresh circuitry.

The RAM in my Mac II is the RAM it came with, save for the 4 MB in bank A. Originally, it was sold to me as a 2 MB machine. Reason being bank A had 1 MB of RAM installed. I swapped that bank with the 4 MB from my Mac SE and the computer suddenly recognized 8 MB of RAM. After installing a 68851 and MODE32, the system suddenly had 20 MB. Turns out bank B had 16 MB of PAL RAM the whole time. I basically multiplied the RAM by 10 from what it originally recognized lol

 

[pathw]

My Mac II with original ROMs (Rev. A motherboard and Rev. A ROMs) and 68851 PMMU and using MODE32 worked fine with 20MB (4x1MB and 4x4MB). System was sold to reallyrandy in 2018. Perhaps he can comment.