The Macintosh Design Team – The Making of Macintosh – Part II (Byte – Feb. 1984)
Steve Jobs and Bill Atkinson (Photo: Norman Seiff)
Jobs: Another thing is that you can run RS-422A twisted pairs, which means I can run these things for several hundred meters. I can string lines if I have a laboratory and a computer on my desk, do whatever I want to do. They aren’t DB-25s. We’ve been living with giant connectors now for years but using only a few of the pins. So, again, we tried to save a little bit of space in the back because the connector space we have is limited. We tried to cut down the cost to the customers again, and so, for connecting to devices like printers and modems, which we offer and which are the most prominent, we just supply the cables. We also will supply cables from one of these things to a variety of DB-25s – for the modem version, the printer version.
Atkinson: Lines 2 and 3 are switched on a modem versus a printer, so you just use a modem cable or a printer cable.
BYTE: From a very early time you knew that you wanted to take advantage of Lisa’s software technology, and you also had the goal of making that possible at low cost. When did you have a consensus on exactly what this hardware would have to be to achieve that goal?
Smith: In 1981 we started looking at the Lisa. I came up with a proposal that said it ends up costing $14 more to use a 68000 with 64K bytes of memory than it does with 6809-based machines, if you count power supply. It turns out that it’s actually easier to interface memory to a 68000 than to a 6809. So in January we started really looking at the 68000 and the work that Bill was doing.
In June of 1982 we finally decided on what we thought was enough video. It turns out that the original machine had 384 by 256 pixels. We chose that because we thought we had a shot at squeezing the machine down into 64K bytes, and we didn’t want to throw away a quarter of the memory just for the screen.
Atkinson: The thing that drove us is the 80 columns. In a word processor, we really wanted the lines to break on the screen at the same place they break on the printer. There are two kinds of word processors. There are the ones where you just have a string of characters and you see them however they wrap on the screen. Screen wrap is a function of the screen, and how characters wrap on the printer is the printer’s doing. Then there are word processors where what you see is what you get. You lay out a line and you know it’s going to break at the same place on the printer as the screen, so you can do columns and tabs and a couple of columns of numbers. Then you have to have enough pixels to generate a full printer line across. We thought we could do it with 384, and we tried it with real live documents – and we couldn’t do it. You could do it with 512, but you couldn’t do it with 384.
Smith: The diagonal lines look better, too; the jaggies are removed somewhat, and things like that. So, with that, we said, OK, what’s that going to mean? And we ended up with 128K and…
Atkinson: 22K bytes on the screen, and in a 64K-byte machine you couldn’t have afforded it. That drove us to 16 RAM chips instead of 8. Hertzfeld: By then, we knew we were going with 128K bytes anyway, to run the applications.
Jobs: I just thought I’d show this to you. This is the IBM video board; it’s only video, nothing else. It’s 69 integrated circuits, more chips than an entire Macintosh, and it basically does nothing. And it doesn’t even do that very well.
Espinosa: Forty percent more chips than the Mac.
Jobs: So that sort of gives you a feeling. And again, that just has the video on it. Macintosh, in addition to having video that’s far higher in resolution and far faster, has a 32-bit microprocessor, 128K bytes of RAM, 64K bytes of ROM, two serial ports, the mouse, the serial, keyboard, and mouse interface, the incredible sound, the clock calendar, the disk controller…
Smith: We rolled the whole disk controller into one chip.
Hertzfeld: And it has Lisa’s graphics and user-interface software built into every board.
Jobs: Andy was sort of the software technical leader behind the project, from its inception. As Andy puts it, software sometimes stands on its head to get rid of a chip in the hardware. And so, with a system as powerful as this, we wanted to take advantage of all the features, for instance, in the serial chip and the disk and stuff. We really wanted to be able to have the serial ports reading while the disk is spinning, while the mouse is moving, while it’s making sound. You know, all with that single board.
BYTE: What were the roots of that operating system?
Kenyon: When we started, of course, we were looking at the work Lisa was doing, and the Lisa group was rolling its own operating system, and it just didn’t seem appropriate. We took the graphics software, which was perfect for our machine.
Capps: The Lisa’s operating system took a lot of the user interface. For the window manager, even the memory manager, we started with what Lisa had.
Hertzfeld: It turns out that Quickdraw is built on top of what Lisa would call the intrasegment memory manager. You relocate little objects. We took that because Quickdraw required that support, and we sort of turned it into our system-wide memory manager. Even the Lisa group uses it only for the intra-application memory manager. Someone mentioned a neat way to do a file system, and we thought about it and said, “Gee, that’s a good way of doing it,” and so we did. A lot of it was experience on the Apple II, knowing what was sort of bad there – what we wanted to do great here. That at least was the conception of the asynchronous I/O. I knew from the Apple II that when you make a disk request it waits there for a whole second, a million microseconds, just waiting for the disk to come up to speed. We should be able to do other useful work while that’s happening. On the Apple II if you want to make a beep, the whole processor, the entirety of the machine, is devoted to making a beep. And when you’ve got all the horsepower of the 68000 there, you don’t want to waste it all on making sounds.
Atkinson: We still make a beep with the processor.
Hertzfeld: But we time-slice the processor such that you can be doing other things. It happens on the interrupt level instead of being dedicated. Macintosh uses the processor for everything, just like the Apple II does. In terms of the disk, we have the same disk-controller architecture as the Apple II, but we are just a little more sophisticated in how we use interrupts. We give the time back to the applications while the I/O is going on.
BYTE: Can you say more about the custom disk controller?
Smith: Sure. A long time ago we sort of figured that everybody who was doing designs at Apple with disks loved what Woz [Steve Wozniak] had done on the Apple II. Ill never forget, the first time I looked at the Woz controller I said, “OK. Well, this must be the interface disk controller. Where’s the disk controller?” I never found the disk controller. And we’ve just been in love with the way that that’s done. It’s used to modify group code. One of the things we knew, though, was that disks would be going faster in the future. So we initially designed this chip so the whole company would be able to have an ultra-low-cost way of using Wozniak’s disk technology for every product. But we knew that we weren’t just going to be going at 4 microseconds per bit, that twice that would become an industry standard … at least an Apple internal standard. So we built in a mode, a high-speed mode, so that it can go twice as fast.
Atkinson: While you’re getting input from the serial port at 19,200 bps, you can be writing to the disk and not missing a beat. It’s not the buffer that’s doing that. It’s Larry Kenyon. Every 4 nibbles, you look to see if there’s something on the port, because in one sector’s time, 24 bytes go by.
Jobs: After we reexamined everything, including the disk format, we said, “Do we want to go to MFM [modified frequency modulation]?” And the more we reexamined it, what became clear was that the original idea that we had for a disk in 1978, which we are still using, is great.
Atkinson: We get 400K bytes on this thing, while most people get only 270.
Jobs: As an example, our scheme has twice the margin of MFM. In other words, when you’re shipping a mil- lion or two million computers a year, which we intend to do, when people are buying media from 10 different sources and they expect to take disks out that were recorded in Alaska in really cold weather and stick them into machines in Florida in a heat wave and have them work, that margin is really important. If you want to equate that to reliability, we are significantly more reliable than any other disk system on the market, while having higher capacity. So that was the key decision, to stick with the same encoding format and the same scheme that we’ve used since 1978. So, while everyone else is running at roughly the same rates as Apple II, the IBM PC, and everything else, we doubled it on Macintosh. We set a new internal standard with the 3V2-inch disk and this new single-chip controller. And every new 32-bit product at Apple will use that new standard. The media, the sector format on that media, the disk controller, and the routines and everything to drive them is a new Apple 32-bit standard that you’ll see com- ing out in every future product that we do in that family.
Smith: There were some voices within the company that said, “Oh, you guys ought to go with standard formats and things like that.” We looked at doing that and it turns out that it takes more chips to interface to a standard floppy-disk controller, and we have…
Jobs: Well, I can go get the IBM floppy board. It looks to have about 45 to 50 chips on it…
Espinosa: I’ll come and help you carry it.
Jobs: .. .including an LSI [large-scale integration] disk controller – far less performance, far less capacity, far higher cost.
Atkinson: And less reliability.
Jobs: Oh, far less reliability. Larry’s software senses the disk speed, and Burrell’s hardware can adjust to one of four hundred speeds. So if it’s written on something that’s a little out of whack, we can just adjust right down to the necessary speed and read it. Everything on the Macintosh board – the serial timing, the disk timings, the microprocessor timings, the video timings, the sound timings – comes from one crystal oscillator and is synchronized from one source. And, again, it’s better, of course, technically to do it that way. Everything works much better, but it also saves parts, and we can offer this thing cheaper to customers. And most of this stuff customers will never ever realize or care about anyway. I mean, who cares how many crystal oscillators you have? But you do care about how big your computer is. You do care about how much it costs, and you do care about how well it works.
Atkinson: If you ever drop your computer you find out quickly how many crystal oscillators you have.
BYTE: So with the variable speed in the disk drives, I guess there’s no problem having two drives that are 3 percent different in speed.
Jobs: We read it and adjust it so that the speed is accurate relative to that crystal. That crystal on the board is superaccurate. We can adjust the disk drive relative to that superaccuracy.
Atkinson: You force all the disks to go at exactly the same speed by having the software constantly monitoring the speed and saying, “Ah, it’s running a little slow; jack it up a little bit,” so that each disk doesn’t have to be adjusted at all. You switch disk drives, and the new one will run at exactly the same speed because you force them all to.
Smith: It turns out that the speed variations occur partly because you plug in a new cassette that loads the motor down in a different way and also because of temperature variations that cause very long-term drifts in the disk speed. Using a little bit of the processor to fix that doesn’t cost us any performance at all on the system.
BYTE: What about the display electronics?
Atkinson: Where is the display controller?
Hertzfeld: It’s hidden.
Jobs: If you bite into that IBM display board, it’ll totally flicker if you do it at the wrong time. You’ve seen that, right? Woz just came up with this really brilliant way to do the Apple II. He realized that memory was about twice as fast as the microprocessor needed it and twice as fast as the video needed it. So he put the microprocessor over here and he put in essence the video over here, and he put some multiplexers in the middle. He shared the exact same memory between the two in a way such that this one thought it had all the memory all the time and this one thought it had all the memory all the time, yet they shared the same memory! All this thing had to do was write into certain memory locations and, magically, it would appear on the screen. The microprocessor never even had to think about the screen. All it did was look at memory locations.
Atkinson: And there was no way to glitch the video because accesses were mutually exclusive.
Jobs: Right. And so it turns out that, try as we might, we have never been able to find a better way to do it.
Atkinson: At the same time that the processors have gotten faster, memory’s gotten faster; the memory is still twice as fast as the processor.
Jobs: And so, again, it gives you greater performance, because you don’t have to write only at special times and slow yourself down. It cuts the chip count way down because you don’t need two banks of RAMs, so the customer’s not paying for these extra chips, and it just makes a more elegant product.
BYTE: How far does the similarity extend between the Apple II video and the Mac’s video?
Smith: We have a three-part memory architecture on Mac. We have a DMA window for sound, video, and CPU… shared by three devices. Also, what we do that is a little more sophisticated than Apple II is return memory cycles to the processor during horizontal and vertical retrace. And with the analog design we’re able to lengthen the horizontal retrace interval, which gives us more performance for graphics by making more time available to the processor from memory and giving the analog electronics more time to retrace the beam. On the Apple II, Woz sort of designed this logic board and the power supply was kind of added. On Mac, we really designed the entire system as a complete system from the ground up, so we used different constraints. I would say there’s not much similarity. The great thing about Mac as a product is that it really wasn’t designed as just this piece over there and this piece over there and this other piece… All of it was designed in parallel, everybody knowing what everyone else’s job was.
BYTE: How did you decide on the appearance of the machine?
Manock: Our goal in the beginning was portability. We actually had this cardboard model that looked amazingly like the Osborne. And that was way before the Osborne came out. As I said, portability was primary here, and this version had an attached keyboard that had a sort of rubber boot around it that would fold up and give you protection over the screen. Steve really changed the emphasis of the product one day when he said that we didn’t want portability to be the primary aspect of this, but we did want it to take minimal desk space. With that goal in mind, we realized that the keyboard didn’t have to be exactly the width of the computer.
Jobs: To use the earlier design you had to have some sort of arrangement to tilt it up. And what we noticed was, well, fine, what if you just lift the back up here like this? Then, because you have all this space underneath, you could put the floppy disk underneath. So you make a unit that’s more vertical, has a smaller footprint.
Atkinson: It has to be up enough so your eyes can see it anyway; you need the height.
Manock: Steve thought, too, I think – in a gut reaction sort of way – that everybody was going low profile and wide, and we never have wanted to be a “me, too.” I think our vertical format is correct when you think of human factors.
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