
Why did Mac OS 7 perform poorly with virtual memory enabled? - bane
https://retrocomputing.stackexchange.com/questions/2804/why-did-mac-os-7-perform-poorly-with-virtual-memory-enabled
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alain94040
_all memory writes are also to disk_

I'm pretty sure that is wrong. What most likely slowed down with VM was that
as soon as a page operation had to be performed, the OS would block and do
nothing else until the disk access was done.

~~~
marvy
How bad is that? If I'm actively using one program, and that program is
waiting on a page from disk, what useful thing can you do in the meantime?

~~~
kstrauser
IIRC, OS 7 was only cooperatively multitasked. If that were the case, and the
program was blocked by the VMM so that it couldn't release the CPU to the next
program, I'd imagine the whole system would hang until the read was finished.

I worked with a web developer in the mid 90's who served some image files off
his desktop Mac. We noticed intermittent hangs and slowdowns during file
transfers. After much head scratching, we pieced together that every time he
held down his mouse button, networking stopped until he let go. This was 100%
reproducible, and 100% hilarious to us Linux folks.

It got eventually got better.

~~~
einr
Sounds like this web developer's computer may have been one of the infamous
Performa/Power Macintosh x200 series[1]. These are _ridiculously_ designed
machines.

Choice quote from [http://lowendmac.com/1997/performa-and-power-
mac-x200-issues...](http://lowendmac.com/1997/performa-and-power-
mac-x200-issues/):

 _One of the biggest complaints about the x200 series is slow Internet
handling. For one thing, looking at the chart above, all data from either the
ports or the ethernet controller must pass through the processor to get to
memory, then be processed, sent to the IDE controller for cache saving, and
then interpreted for graphics display.

There are symptoms to notice because of this. While a web page is loading,
typed characters will be lost. When dealing with high IDE access, the graphics
controller will seem to freeze. When copying to a network or downloading a
file, the monitor will rarely update and will have redraw problems. Spooled
print jobs will take forever if lots of processor resizing is necessary._

[1] [http://lowendmac.com/2014/power-mac-and-
performa-x200-road-a...](http://lowendmac.com/2014/power-mac-and-
performa-x200-road-apples/)

~~~
kalleboo
When I was a kid we had a Performa 5200, and I suffered from this. We also got
a surplus Quadra 800 with a 66 MHz PowerPC upgrade from my dad's work - which
outperformed the 75 MHz Performa in everything aside from MP3 decoding.

We also ran into the serial port issues the article describes, we got better
performance hooking our 56k modem up to the Quadra and sharing that connection
to the 5200 over LocalTalk via IPNetRouter than actually using the modem
directly.

~~~
Angostura
Didn't the Performa use the PPC 603? ISTR it did. The 603 was the 'cheap-n-
cheerful' chip in the family, I suspect the Quadra upgrade would have had a
601 or 604, both of which had more oomph.

~~~
kalleboo
Yeah doing the research now - the 5200 had a 603 @ 75 MHz, and the PowerMac
PDS Card had a 601 @ 66 MHz. I was also reminded the 603 had too small of a L1
cache to hold the the 68K emulator, reducing performance even further...

Now I'm curious what made the 5200 better at MP3 playback. My recollection is
that the only way to get the upgraded Quadra to play MP3s in realtime was with
SoundApp monopolizing the CPU so you couldn't even click anything else. On the
Performa, you could run MacAmp in the background while browsing the web, with
stuttering "only" during whole page repaints. This was 20 years ago, my
recollection could be poor... I soon got my own Quadra 660AV (video
digitizing!) and eventually a PowerMac 7500 (that I upgraded to G3 and could
even run early versions of OS X with Xpostfacto)

~~~
bluedino
I had a 5200, and I had AOL Instant Messenger installed. I'd be working away
in some other program, and then the whole thing would freeze for a second, and
repaint, every time I got a new IM and was using another program.

After a few days of that crap I just installed YellowDog Linux.

------
inetknght
> If the OS and apps you needed to run required 4MB RAM, then you really
> should have at least 4MB RAM. [...] Set your VM page size to only 1MB more
> than your physical memory size.

ahhh... I'm fond the days from when you could run whole applications in all of
4MiB -- GUIs included.

~~~
dreamcompiler
Yeah. I had a colleague who used Photoshop a lot. She got management to spring
for 30MB of RAM for her machine. I thought that was the most outrageous thing
I'd ever heard.

~~~
jamesfmilne
My father used to run a desktop publishing bureau that output people's print
jobs onto film, which was then sent to printing presses for printing. This was
for magazines, artwork for packaging, etc.

He had a Quadra 950 with 128MB of RAM, which required some pretty exotic
SIMMs. That would be a pretty expensive machine in today's money. This was for
handling Adobe Illustrator files with large embedded images.

~~~
yuhong
Ah, 16MB 30-pin SIMMs. One of the reasons they were not popular was that the
first 16Mbit chips was 400 mil, making them pretty tall

