Friday, 5 May 2017

25/26 Years since... the Mega STE

2016 should have been all about the 25th anniversary of an Atari ST released that ran at 16mhz. Except that 1991 was a terrible time to be releasing computers. There was a huge amount of competition, and besides this 5 years earlier, someone had been there, done that and done it properly…

30 Years Ago... 

So, we go back in time to 1986/87.   Apple developed a computer that could run multiple monitors, in colour, at 16mhz, and not be slowed down by ram having to share memory with video or be accessed 16 bits at a time.   This was the Macintosh II (released March 2, 1987)

All about RAM and performance

So you’d think I could just type into google Mac II memory bandwidth and get the answer. Unfortunately not. The simple answer is its got a 16mhz processor that accesses memory in 32 bit chunks (ie; a true 32 internal and 32 external design). Unfortunately the cost was between $6-8000 for a fully functional system (1mb ram, 40mb hdd) possibly reducing to $3000 over time.. So it made sense where a business needed any of these features.

A nice summary of the system (Macword Macintosh II celebrates 25th anniversary)

A clear leader?

So you think that would be the end of it, Apple just need to keep stomping on the competition as this is still better than anything anyone else can produce.   Maybe reduce the price or number of slots, but keep everything else the same.  Moore’s law would let you develop the next generation (eg; 20, 25, 33 mhz) motherboards and cpu’s and sell them at the premium prices, and then advertise lower spec machines that come from the exact same production process.

Project Lower Cost (LC)

But instead they stomped on themselves and went to plenty of effort developing machines that were cheaper and less expandable.  One of these options was the Mac LC, released in October 1990 [introduced 1990.10.15 at $2,400], which had more colour than any Atari Mega STE without graphics card and cost $3000 (including hard drive and monitor).. Even cheaper was the Mac Classic II ($1900, 2mb ram, 40mb hdd), released in October 1991 which had no external monitor options (and resolution was limited to 512x342 in mono) which seems to have better performance than the LC.

A comparable Mega STE?

Realistically, the Mega STE wasn't released with additional graphics options and wasn’t well publicised* at the time of its announcement.  In theory I can claim it could have sold for £629 (no hdd)/£799 (1Mb) or £929 (£1149 including 12" mono monitor) and 48Mb hard drive (2Mb). (Its hard to find advertising for it in 1991 ... It seems to have been announced in 1990, and trickled into existence in 1991 and Atari printed an advert in November 1991)..
So the Mac classic II is probably about 25-30% more expensive for the same config with smaller screen and smaller hard drive.. released within 2 months of one another.
*Prices from 1st choice computers December 1991, Power Computing April 1992.

Next generation CPU

And then there’s the architecture differences.. The Mac LC used a 32 bit processor* on a 16 bit bus, but had separate vram (video memory), and so ran at 16MHz without cache. The Mega STE used a 68000 processor on a 16 bit bus, with a cache. Performance was close but not quite 2x the speed of a normal ST (with the cache enabled. With cache disabled, there was almost no noticeable increase in speed -- ST Review) so it’s hard to tell which one was actually slower from these descriptions..
But the cpu architecture, the separate video ram, will have meant that definitely the LC was faster even with descriptions such as “the 16 MHz 68020 based Macintosh II from 1987, with an identical processor, ran almost twice as fast as the Macintosh LC”

The advantages of the 68020 over 68000 are 32 bit ALU so 32 bit maths happens in less clock cycles and it has an instruction cache, so there is not as often a need to access ram to fetch after each instruction.   And the LC used the 68030 which has a memory management unit (MMU) which is also very important for running programs more reliably.
The consequences of these design choices can be summed up in one chart that shows that 68030 based macs all running at more than 2x the speed of any 68000 8Mhz traditional mac.
Speedometer 3.06 from low end mac []
Macbench 2 results are more conservative, showing the slowest 2nd generation mac scoring 0.87 vs 0.37 for 8mhz machines. []

Actual Atari Benchmarks

Of course that still leaves a couple of questions about speed which remain unanswered, - is an 8mhz Atari faster than an 8MHz mac and therefore could a 16MHz Atari be faster than a 15.6672MHz mac.  I don't think there's a simple answer to that, but from the architecture design discussed so far, I would say the same code doing cpu bound stuff (raytracing, spreadsheets) etc, you're only going to see the Macs win.
The operating system on the Mega STE might be enhanced for speed (eg; printing over parallel vs serial, text display enhancements like NVDI, potentially careful use of the blitter) but ultimately, its all trying to fight an uphill battle.

That's all for now.  I was going to add a video of someone else's take on the Mega STE and just to say its extremely compatible with existing STE applications and software and they later enhanced it with a new rom: the advanced TOS 2.06 and high density (1.44meg) disk drives.  The other thing the Mega STE has is a vme bus which gives extra graphics options.. which makes it very expandable. ok out!

This video by Dr Steve Bagley gives you a little idea of what they look like.

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