Building the System/360 Mainframe Nearly Destroyed IBM

This whole thing is very cool and worth reading.

BUT. I worked at a place that used IBM 360s. We ran stuff for engineers, a lot of Fortran along with assembly code. We had so much stuff going on we could not code up and run things fast enough. The engineer/scientist got frustrated.

Then one day an engineer brought in an Apple II from home and ran the programs on that.

The earth shook. The very ground beneath us moved. Tectonic plates shifted. The world was never the same again! I think it was Visicalc.

Later there were other things. Soul Of A New Machine. The Mac.

I wonder how the compute power of a current high end smart phone compares with and IBM 360? I know the graphics chip is better.

A $50 smartphone is many orders of magnitude faster.

If I had to compare computers based on one number it would be the amount of RAM. The 360 had a 24 bit address space which could fit 16MB of RAM although only the largest installations, like the one at NASA, were that big. iPhone 16s have 8GB of RAM so you're talking 512 times the memory capacity, never mind that my desktop PCs are all loaded with 4-8x times that of the phone and you can definitely get a big server with a few TB.

An IBM 360/20 on the small side, however, ranged from 4kB to 32kB which was similar to home computers circa 1980, before it is routine to have a complete 64kB address space.

Where the 360 crushed home computers was in mass storage, 9-track tapes could store 80MB contrasted to floppy disks that stored less than 200kB. Large storage compared to memory meant a lot of focus on external memory algorithms, also there was already a culture of data processing on punched cards that translated to the 360 (e.g. terminals have 80 columns because punched cards had 80 columns)

>BUT. I worked at a place that used IBM 360s...Then one day an engineer brought in an Apple II from home and ran the programs on that.

The 360 was introduced in 1964. The 370 was introduced in 1970. The 3033 was introduced in 1977. The Apple 2 was introduced in 1977. So, yeah, if you were still using 360s contemporary with an Apple 2, no wonder the engineers were frustrated.

Where the 360 crushed home computers was in mass storage

Well...sure, you could put bigger storage on a mainframe. It's just money, after all. But you could put a tape drive on a home computer. And bigger disks. And a card reader, for that matter. Where the 360 really crushed the home computer was in aggregate bandwidth, via the Channel architecture. An Apple 2 could just about keep up with a floppy and a display. A 360 could keep up with dozens to hundreds of tapes, disks, card readers, terminals, printers and other things all at the same time.

Large storage compared to memory meant a lot of focus on external memory algorithms

I would agree with that. I would just argue the real mainframe advantage is a whole-system one and not point to a single factor (memory size).

I wonder how the compute power of a current high end smart phone compares with and IBM 360? I know the graphics chip is better.

A current high end smartphone has around 10 billion transistors.

From https://gunkies.org/wiki/IBM_System/360, IBM made 11-12 million SLT modules per year in the late 1960s, with less before that. Each individual SLT module contained a handful of transistors. Therefore, in transistor count alone, a single smartphone has more transistors than IBM produced through the 1960s. And this is before we consider the fact that clock speeds today are much higher than they were in the 1960s.

Your smartphone literally has enough hardware to outcompute the entire world circa 1970.

Isn't it amazing what over 50 years of Moore's Law can do?

Huh. The article claims at least an order of magnitude more SLT modules than the reference I found. I think it is still quite a bit less than the smartphone, but that makes global compute at least closer.

Still, 55 years of doubling transistors at a given cost every 2 years is about a 190 million fold transistor difference for a given cost. Clock speeds have improved by a factor of 1000 on top of that. Even with performance tradeoffs for battery life in a smartphone, there is no surprise that the phone should have more compute power than the world did in 1970.

Indeed. I find it interesting to look at the generational outliers on that curve: The Cray-1 wasn’t eclipsed in raw FP compute by a consumer system until the Pentium more than 15 years later.

http://www.roylongbottom.org.uk/Cray%201%20Supercomputer%20P...

How many years old was the s/260 at this point? If it was really long in tooth then I wouldn't be surprised.

Most of the outliers look like, "Someone was willing to spend large amounts of money."

Another outlier was Deep Blue. Estimated cost of about $10 million. Its estimated strength was matched by top end PCs about 9 years later. Your phone today is better than those PCs.

Progress is relentless.

The 360 had 24-bit addressing, for a maximum of 16 megabytes.

The 6502 in the Apple could address 64k of RAM. Any class of problem requiring more memory would need a real machine.

As far as a personal machine with comparable capability, RISC brought that to the market with the first MIPS R2000 in 1985.

https://en.wikipedia.org/wiki/MIPS_architecture

My home NAS in the other room could hold about 350 million C64 floppies. I've sometimes wondered how that compares to the world's floppy disk manufacturing capacity in 1982.

I also appreciate that my Internet connection is about 33 million times faster than my first modem. It'd take me over a year to download what I can slurp in about 1 second now, even if I could afford the 7 thousand floppies it'd take to store it.

Progress, yo.

The Motorola 68000, introduced in 1979, had 24 address lines. The Intel 80286, introduced in 1982, also had 24 address lines.

Well, the VAX was there before any of these, but I wouldn't call that a "personal machine."

I suppose the argument could be made that the 68000 was first, as both it and MIPS ended up in gaming consoles (Sega Genesis vs. Sony PS2 and Nintendo 64).

However, MIPS eventually scaled to 64-bit, was well-known and heavily exploited in supercomputing applications, and was used to produce the film Jurassic Park. The 68000 had a far dimmer future.

Yes, the x86 line did supplant them all, but only with AMD's help. Had Itanium been Intel's final answer, MIPS might be much stronger today.

> I know the graphics chip is better.

Graphics? We used these machines with 9600 baud serial terminals.

The most powerful 360/91 was roughly equivalent to a 20MHz 486 from the early 90s.

Mainframes had much more powerful distributed IO for multiple hard drives, tape systems and such.

But the CPUs were really not all that powerful at all.

Many people wildly underestimate just how insanely fast and power-efficient today's commodity computing is compared to high-end supercomputing from earlier decades.

A Raspberry Pi destroys any supercomputer earlier than around 1990, and gives some later models a run for their money.

An Apple S7 watch processor is maybe 25X faster than a Pi 5.

And so on.

Lots of organizations run those computers for very long times. It was not unusual for a medium-sized company, a factory or some local government to be running 10 to 15 years hardware.

I am not sure about the 360’s terminals, but some terminals could display graphics via sixels. Konsole and xterm are capable of showing them in the present day if you run a terminal copy of word perfect.

> the entire world circa 1970.

About then was the IBM 360/91 with a 60 nanosecond cycle time. So, that would be a clock speed of

     1/ ( (60)/(10^9) ) 

     = (10^9) / 60

     = 10^7 (100 / 60 )

     = 10^7 (10 / 6 )

     = 10^7 (1.66)

     1.66 (10,000,000)

     16.66 (1,000,000)

     = 17 Mhz

Now we can have clock frequencies of 4 GHz, that is

     4000/17 = 235

times faster. And we can have 16 cores instead of 1 for

     (16)(4000) / 17 = ~4000

times faster. "entire world"?

Never mind a high-end or even low-end smartphone, I think a Raspberry Pi would absolutely dominate these old machines.

Comparing like-for-like (tape storage), you can now buy 45TB tape cartridges. That's a 500,000 times improvement per tape.

Edit: apparently these cartridges actually are 18TB, 45TB is "compressed" capacity. Still though, terrible marketing aside it's still factor of 225,000.

I agree. I did writeups on order of magnitude of RAM and computers over history:

https://saul.pw/mag/memory

https://saul.pw/mag/computer

The IBM 360 is ^4 RAM and the iPhone is ^8 RAM. So the iPhone is ~10,000x more powerful.

What’s the average IPC of these chips for a reasonable workload?

Early processors were typically 1 or lower. Modern stuff is all superscalar piplined and out of order and can do way more than you’d expect. Not to mention SIMD operations and other technologies. Branch prediction is probably better on the new chips too.

And with more RAM and cache algorithms can be chosen with different tradeoffs for less instructions.

16 cores at 4ghz was a thing like a decade ago - chips today might have the same specs but are definitely far faster.

WOW! IPC, instructions per cycle? Sure, back in those days, usually how many cycles per instruction! The 360/91 was a high end thing, said to cost $13 million. One was at the Navy lab, JHU.APL. As I recall, it could do 1 floating point (32 or 64 bits?) instruction per cycle and sometimes 3 in 2 cycles.