Testing a 6200

I wrote this mostly over a year ago but haven't clicked post. I wanted to do a bit more, but things have conspired against it so I thought I'd share.

I'm actually nervous posting it because people are so passionate about these machines, one way or the other.

I tried to do testing as fairly as possible to see where the performance differences were, and experimented to see where improvements could be made.

The biggest thing I learnt along the way is that SpeedDoubler is a mandatory install for beige PPC macs if you run any 68k code on them at all.


@cheesestraws @joshc @Snial @Cory5412

Interesting read...

Phipli said:

I wrote this mostly over a year ago but haven't clicked post. I wanted to do a bit more, but things have conspired against it so I thought I'd share.

I'm actually nervous posting it because people are so passionate about these machines, one way or the other.

I tried to do testing as fairly as possible to see where the performance differences were, and experimented to see where improvements could be made.

The biggest thing I learnt along the way is that SpeedDoubler is a mandatory install for beige PPC macs if you run any 68k code on them at all.

An Extremely Tardy Performa 6200 Review

An Extremely Tardy Performa 6200 Review… … or how slow is the “worst Mac” when you actually spend some time gathering primary evidence, including experimenting with various …

elephantandchicken.co.uk

@cheesestraws @joshc @Snial @Cory5412

Click to expand...

Reading this now ! Since @noglin is a P5200 fan, I thought I'd notify them here! OK, you mention Noglin later.

Based on my analysis of disk partitions on my PB1400c, as standard it will come with the 68K IDE driver, but Mac OS 8.1 and later will install the PPC driver (on a different driver partition).

Suggested edit: "Based on in which benchmarks the Performa 6200/75 performs least we’ll compared to the PM 6100/66", I think "we'll" is a typo and should be ", well".

@Snial

The main issue seems to be graphics speed based on testing of this specific machine.

Given the 630 is faster, and tests show that it isn't due to 68k driver code / quickdraw code, the hardware is clearly capable of more.

Possible issues are the number of wait straights they had to add for the increased bus speed, or something nasty to do with the bridge. What did I see that might be a clue - it is good at writing images to the frame buffer compared to the 630, but bad at translating an image in VRAM.

Given they had a few issues early on, I wonder did they detune the video performance heavily to avoid crashes? Bad performance over stability issues?

I'd love to compare a release day ROM to see if graphics performance is better.

Also, I hadn't thought before, but I wonder what it would be like with an LCPDS video card?

Also, how differently does a 6300 (5300) perform? How about when underclocked to 75MHz?

So many questions.

Regardless, the results weren't what I was expecting from what I've previously heard from either advocates or detractors.

Snial said:

Suggested edit: "Based on in which benchmarks the Performa 6200/75 performs least we’ll compared to the PM 6100/66", I think "we'll" is a typo and should be ", well".

Click to expand...

Yeah, that's a phone autocorrect - it is been a nightmare lately. It keeps editing valid text like changing "of" to "if", but only after I look away and press space. It is also frequently breaking words that start with a more common word by forcing a space mid way through the word. I strongly feel auto correct has got much worse over the last 15 years. It tries to be smart and is worse for it.

Phipli said:

The main issue seems to be graphics speed based on testing of this specific machine.

Click to expand...

So, if @noglin pops up on this thread, then they probably have the best insight.

Phipli said:

Given the 630 is faster, and tests show that it isn't due to 68k driver code / quickdraw code, the hardware is clearly capable of more.

<snip> wait states they had to add for the increased bus speed, or something nasty to do with the bridge. What did I see that might be a clue - it is good at writing images to the frame buffer compared to the 630, but bad at translating an image in VRAM.

Click to expand...

Sounds plausible. I thought I was going to find a 68040 bus signal diagram here:


And I'm sure I've seen it before, but I couldn't find it. The P5200/6200 need 80ns RAM, but I guess the '040 bus runs at 37.5MHz? There's some extensive discussion I'm sure you're aware of here:


Noglin suggested that the graphics slowdown is due to the write buffers on the PPC/'040 bridge. Graphics writes likely use stfd instructions, which write 64-bit values, but these get broken down into 2x 32-bit writes, so even a single write fills 2 write buffers. Hence it functions as a bottleneck. He did numerous graphics tests which identified huge bus latencies depending on how much data was being shuffled and processed between caches and the '040 bus.

Phipli said:

<snip> compare a release day ROM <snip> LCPDS video card? <snip> 6300 (5300) perform [75MHz]? <snip>

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oK.

Phipli said:

Regardless, the results weren't what I was expecting from what I've previously heard from either advocates or detractors.

Click to expand...

I guess these machines are contentious, because they were pioneering consumer PPC Macs, leading to Workstation level over-expectations for some people (not me, my first experience with a P5200 I felt was awesome vs my LC II :-D ).

Snial said:

I guess these machines are contentious, because they were pioneering consumer PPC Macs, leading to Workstation level over-expectations for some people (not me, my first experience with a P5200 I felt was awesome vs my LC II :-D ).

Click to expand...

They're excellent spreadsheet machines. Especially if you're doing lots of FP and the version of Excel supports the PPC FPU.

@Snial - I should probably share this here too for background, although I think I showed you specifically before :