Macintosh SE

[Macflyer]

Okay,

I did some reading yesterday about the SE. Seems the SE was the improved Plus. It works between 10-20 % faster, option for internal HD, later models with Superdrive, PDS slot, "better" cooling. Improved on almost all aspects.

But, why does it only support up to 4 MB like the Plus? Or, are there easy hacks to get it use more?

Then, could a power supply from a late SE serve in the SE/30, since I will need to replace it in the long run and prices are in favour of getting an SE than shopping for a replacement part or a SE/30 on ebay. Couldn't find reliable info on the net plus I'm not much of a technician (yet) to know what to look for to be compatible but Watt&Volt.

 

[System6+Vista]

I'm almost 100% sure that'll work. I think you only start to see differences once you get to the motherboards.

No, you can't hack more than 4mb into a SE because the logic board architecture wasn't designed to support it. If you're running system 6, 4mb isn't so bad for most things!

 

[trag]

But, why does it only support up to 4 MB like the Plus? Or, are there easy hacks to get it use more?

The MC68000 CPU used in the Plus and SE only has 24 address bits. Twenty-four bits yields 16M (about 16 million) addresses. So they devoted 1/4 of the address space to RAM.

They probably could have gotten it to 8 MB without too much trouble....

But, for the original design, look at what the bits do. Any address in which the first two bits are zero can be ignored by all the hardware except the RAM. Then those two upper bits can be used as code for which addresses are directed to which I/O hardware.

If they had spent 8 MB on RAM or one half of the address space, then there would only be one bit to use for simple address decoding. Instead of decoding the upper two bits into four combinations, the hardware would look at the single bit which says, "RAM or Not RAM" and then it would also have to look at the lower bits in the cases where the answer was "Not RAM".

So keeping the RAM to 4 MB may have achieved a significant savings in address decoding hardware. I'm not certain it did in reality, because I don't have the Mac Plus address map sitting in front of me, but it's published in "The Guide to the Macintosh Family Hardware".

 

[phreakout]

To answer your questions Macflyer, the Mac SE can address up to 8MB of RAM, provided you have a Processor Upgrade Card for the SE. It was a PDS expansion card that piggy-backed on top of the original stock Logic Board. You would have 4MB RAM on the stock Logic Board and 4MB RAM on the Processor Upgrade Card. Technically, it was called an accelerator card or expansion card. Some of these cards featured a 68020 or even a 68030 processor in addition to the more RAM.

The SE and the SE/30 are 100% compatible in power supplies, analog boards, CRT and logic boards. You can swap out the parts without fear of incompatibilities. I have already done this myself with my SE. When my SE logic board's ADB ports stopped working, I bought an SE/30 logic board from user MacG4 and replaced logic boards with no issues. It gave me a faster processor (68030 16 Mhz vs. 68000 8 Mhz) and I can install up to 128 MB RAM max total. The only minor difference is that the SE/30 upgrade does generate more heat, due to a faster more powerful processor and the 68882 chip.

73s de Phreakout.

 

[Mac128]

To answer your questions Macflyer, the Mac SE can address up to 8MB of RAM, provided you have a Processor Upgrade Card for the SE.

The Macintosh Portable is for all practical purposes a Macintosh SE. It too had an expansion slot which many developers used to add as much as 9MB RAM, though Apple did not officially support more than 5MB (originally only 3MB!). The backlit model limited the maximum to 8MB as does the PB 100. Many 68030 accelerators for the SE would also allow the maximum 24-bit RAM support of 16MB for the SE & the Plus. The SE has plenty of wasted space in its address map which is presumably how the Portable manages to support the extra RAM.