MODE32

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MODE32 was software originally manufactured by Connectix for some models of the Apple Macintosh . It was sold at $ 169 from 1991 until September 5, 1991 , when the software became available for free under the license terms of Apple Computer .

overview

MODE32 fixes a bug that was in the ROM of some early Mac models (see below) from 1989–1990. It prevented the use of more than 8  MiB RAM under System 7 . These computers were originally developed at a time when the operating system was not yet 32-bit capable and therefore the 24-bit addressing that was common on Macs at that time was used. After the release of System 7, this error came into play because the Mac SE / 30 could be equipped with up to 128 MiB RAM.

Connectix put the fix up for sale until customer dissatisfaction led Apple to sign a licensing agreement with Connectix.

The software installs itself as a control panel in System 7 and enables the »32-bit addressing« option to be selected in the memory control panel. This option is not available without MODE32.

MODE32 is only required on the affected models under System 7, and only with more than 8 MiB RAM. Under System 6 , Connectix OPTIMA can be used to use more than 8 MiB for programs, or Maxima for a RAM disk in this area. Very old Mac software, typically from before 1990, may not work. May not be 32-bit suitable and must be operated in 24-bit mode.

32-bit compatibility

In the case of 24-bit programs, the upper 8 bits of the address register , which in the Motorola 68000 processor are not routed to the outside via connecting lines, were used for internal purposes. The use of such software on real 32-bit platforms leads to incorrect addressing of memory accesses. Due to the missing or limited memory protection of System 7, starting such a program usually resulted in an immediate system crash .

Affected Devices

All other Macs do not need MODE32, as they either do not have 32-bit addressing, no more than 8 MiB RAM can be installed or the ROM has already been delivered error-free and thus offers 32-bit mode itself.

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