MAC OS 7.6 DISK CACHE SIZE CODE
The Virtual Memory Manager takes special steps to avoid double page faults caused by user code (that is, code that is not executed as the result of an exception).
Looking through the documentation, it's not hard to see why performance could suffer. I would say poor performance was due to System 7's implementation, and the constraints needed to support existing applications/drivers/extensions. If you found this information useful, please give credit where it is due and upvote the original comments. SourceĪll of this information was sourced from /r/retrocomputing and /r/VintageApple. You got used to the workflow of doing as much work as you could in a single app and only switching to another app when there was something that you absolutely had to get done there If you lived on a diet of "low impact" programs, application switch time was tolerable if not speedy. You'd see things "perform poorly" when you were switching from one memory-hungry app to another memory-hungry app (e.g., PageMaker to Adobe Illustrator) and that performance hit would only last as long as the process of switching between the apps. Set your VM page size to only 1MB more than your physical memory size.
If the OS and apps you needed to run required 4MB RAM, then you really should have at least 4MB RAM. VM performance suffered greatly if this wasn't done. However, many performance with virtual memory were caused by incorrect configuration or use.ĭefragment and optimize the hard drive. Presumably to ensure compatibility with older hardware, System 7 didn't use DMA for disk access.ĭisk I/O on most Macs was done by using the CPU to do transfers Not using DMA meant that any transfer of data between disk and memory for paging required the CPU to do all the work.Ĭomputers that use DMA run programs while the transfer ran, so Windows machines felt faster with virtual memory. Sourceįor the 68020 was a coprocessor that many machines like the MacII had sockets for. System 7 was designed to run on those 68k Motorola processors The Intel 386 on the other hand had paging file management built in. Some portion of the main processor was dedicated to maintaining the paging file on the HD. The processor and MMU (or lack thereof) significantly affected virtual memory's performance. Some applications, like Photoshop, kind of did their own via temp files In some cases you might have two writes contesting for resources.
Many memory-hungry programs developed before virtual memory were designed to cope with low-memory computers in a similar way to System 7.
MAC OS 7.6 DISK CACHE SIZE PLUS
It keeps ALL of the contents of memory in the VM Storage file, plus however much extra you've set it to, so all memory writes are also to disk also, even if not all reads are. The implementation had a significant effect. There are several reasons for the low performance of virtual memory.
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