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PRODUCT PREVIEW: The Apple II GS
The 65C816 processor brings the Apple II into the 16-bit world.
by Gregg Williams and Rick Grehan
Editor's note: The following is a BYTE product preview. It is not a
review. We provide an advanced look at this new product because we feel
it is significant. A complete review will follow in a su bsequent
issue.
The Apple II has a curious history. It was originally designed by Steve
Wozniak and Alan Baum in 1976 as a homebrew computer that squeezed
maximum features out of minimum parts. Over the years, it evolved into
the Apple II+, then the IIe, then the IIc. Once, Apple tried to kill it
off with the Apple III (which itself died) and, later, with the
Macintosh and the IIc. Despite corporate attempts to ignore it and
retard its evolution, the Apple II continued to bring in the major part
of Apple's income. Finally, in May 1984 Apple acknowledged the reality
of the Apple II's success when it titled its day-long introduction of
the Apple IIc "Apple I I Forever." (Despite Apple's wishes to the
contrary, the IIe continued to sell better than the nonexpandable
IIc--people wanted their expansion slots.) By mid-1985, though, the
Apple II began to lose its sales appeal, and Apple engineers were
already working on a product called, at various times, Phoenix,
Columbia, Cortland, and Granny Smith: the Apple II GS.
The Apple II GS looks back to the past and forward to the future, and
the machine might best be summarized by saying that it takes a giant
step in both directions. Its new styling and modularity (see photo 1)
foreshadows a day when Macintosh and Apple II products will use the
same keyboard and 3-1/2-inch disk drives.
System Description
Here are the most important features of the Apple lI GS: Apple II
compatibility: The Apple II GS will run most Apple II software and
expansion cards. It can run at normal Apple II speed or at a higher
rate that makes most software run two to three times faster. [ Edit
or's note: In this article, "Apple II" refers to the traditional Apple
II computer as defined by the Apple II, II+, lIe, and IIc. ] The Apple
II GS composite video signal has been corrected so that it will be
recorded correctly by a videotape recorder. Apple lie owners can
upgrade to complete II GS compatibility by replacing the motherboard
and back/bottom plate with a II GS retrofit kit. A 16-bit,
6502-compatible processor: With a 16-bit address bus and 8 "bank
address" lines, the Western Design Center's W65C816 can address 256
banks of 64K bytes each, for a total of 16 megabytes. It can also go
into a 6502 mode, where it emulates the 65C02A used in the Apple lIe
and IIc. The processor's accumulator, stack pointer, and all its
registers are 16 bits wide, and its instruction set includes 11 new
addressing modes. Greatly expanded memory capacity: The machine's
architecture reserves space for 8 megabytes of user RAM and 1 megabyte
of system ROM. It comes with 256K bytes of RAM, 128K bytes of system
ROM, and 64K bytes of dedicated sound-wave-form memory, but you will
have to wait for new programs to use most of the memory above the first
128K bytes. Apple currently has plans for 1- and 4-megabyte expansion
cards, although an 8-megabyte card is possible. New graphics
capabilities: The Apple II GS adds two "super hi-res" graphics modes:
200 by 320 pixels with a 16-color palette and 200 by 640 pixels with a
4-color palette: the colors come from a color set of 4096. The machine
can use up to 16 palettes per screen and change palettes and resolution
on a line-by-line basis. Programmers can use two experimental modes: a
640- by 200-pixel, 16-color (with restrictions) palette mode, and a
high-speed "fill mode" variation of the 200 by 320, 16-color mode. New
sound capabilities: The 32-voice Ensoniq Digital Oscillator Chip (DOC),
used in the Ensoniq Mirage sampled-sound music synthesizer, and system
firmware can drive the chip to prod uce up to 15 musical "instruments."
Mouse, keyboard, and disks: A one-button mouse and a detachable
keyboard with keypad are standard equipment. The Apple II GS does not
have an internal disk drive, but you can daisy-chain up to two
800K-byte 3-1/2-inch drives and two 140K-byte 5-1/4-inch drives to the
disk drive port on the rear panel. The system software will come on
3-1/2-inch disks, which silently but forcefully indicates Apple's
intent to phase out the 5-1/4-inch floppy disk. The Toolbox:
Application programs can use built-in code (some in ROM, some in RAM)
to provide a mouse-driven desktop environment and orderly use of system
resources. The Finder: Finder software, supplied with the basic system,
allows users to interact with disks and files using windows, icons, and
a mousedriven cursor (as popularized by the Apple Macintosh). Desk
accessories: The Apple II GS makes available Macintosh-like desk
accessories; some a re available from all programs, and others work
only with programs specifically designed for the Apple II GS. The
Control Panel, accessible from any program, allows the user to change
the date, slot assignments, operating speed, and similar parameters.
New languages and tools: For the software developer, Apple will offer a
6502/65C02/65816 assembler and versions of C and Pascal; the three
languages share a standard editor and linker and allow object code
modules from any source to be used together. For the hobbyist, Apple
has extended the Apple IIe monitor to work in the Apple II GS 16-bit
environment and has added new functions to it. No enhanced, built-in
language: Like the Macintosh (and unlike most other computers), the
Apple II GS contains no built-in language (such as Microsoft BASIC)
that interacts with the machine's new features. Applesoft BASIC is
available in system ROM, but it has no way of directly interacting with
the new Apple II GS features. A new 16-bit operating system: ProDOS 16
extends Apple's ProDOS (which runs on the Apple II+, IIe, and IIc) to
be the standard Apple II GS operating system; it runs on the 65816 in
native 16-bit mode, is functionally similar to the 8-bit ProDOS, and
shares an identical file structure with ProDOS. Apple has also made
slight modifications to the 6502-based ProDOS so that it will run on
the Apple II GS's Apple II emulation mode; this operating system is
named ProDOS 8.
Two Machines
The case of an Apple II GS contains, in a sense, two machines: the full
Apple II GS, with all its memory and new features, and a 128K Apple
IIe. Much of this article will explain the design elements that allow
these two "machines" to exist together. You may want to refer to figure
1, which is a block diagram of the Apple II GS.
The Mega II
The Mega II is a custom CMOS chip containing about 3000 gates and a
2K-byte by 8 ROM (for the character generator). It replaces the fol
lowing chips from the Apple IIe and IIc: character generator ROMs for
eight languages, several TTL chips that perform logic functions, and
the MMU (memory management unit), IOU (input/output unit), TMG (timing
generator), and GLU (general logic unit) custom chips.
In previous Apple II designs, the refreshing of memory was tied
directly to the Apple II video mode. The Mega II includes an 8-bit
counter for refreshing the 128K bytes of (slow) memory associated with
the Apple IIe/IIc model; it does five cycles of RAM refresh during the
horizontal retrace of each video scan line and refreshes the 128K bytes
of memory in 3.25 milliseconds. By taking care of RAM refresh, the Mega
II chip opens the Apple II design to new video modes that were
impossible before.
Speeding UP the II GS
The Apple II GS designers had many conflicting goals. They wanted to
make a machine that runs as much existing Apple II software as possible
and to make it run software (both old and new) faster than on an A pple
II. In order to accomplish this, they changed the memory map and
employed a technique called shadowing . Figure 2 shows the Apple II GS
memory map. Remember that many memory areas in the Apple II are
special; the memory-mapped "soft switches" in the C000-C0FF hexadecimal
region control many key functions, interaction with the peripheral
cards occurs through locations in the C100-CFFF hexadecimal region, and
several areas of memory determine what graphics and/or text are shown
on the video display. Many of these areas are limited by the original
Apple II design to being accessed at 1 MHz. A straightforward expansion
of the Apple II design would put the slow memory in banks 00 and 01,
their location in the Apple IIe and IIc. (A bank is defined as the
64K-byte address space from hexadecimal location XX0000 to XXFFFF.
Actually, the two 64K-byte banks of memory in the Apple IIe and IIc are
called simply the main and auxiliary banks, but you can imagine the
bank select as the 17th bit of the corresponding Apple II GS memory
address.)
Instead, the designers put the slow memory (with the corresponding
control circuitry) in banks E0 and El hexadecimal and assigned fast
memory to banks DO through 7F. This gives you 8 megabytes of linearly
addressed memory (something new to Apple II programmers), and all
existing Apple II programs (which must run in banks 00 and 01) will run
in fast, not slow, memory, (The 65C816 runs at 2.8 MHz, but the
overhead of dynamic memory refreshing slows the average speed of RAM
memory access to about 2.5 MHz; ROMs are accessed at the full 2.8-MHz
speed.)
This scheme gives us speed but not compatibility. Programs that do I/O
using the peripheral slots and video display write to addresses in
banks DO and 01, but the hardware they need to interact with is tied to
the slow memory in banks ED and El hexadecimal. How can we get this
scheme to work?
The answer is shadowing. The Apple II GS engineers designed the Fast
Processeor Interface (FPI) cu stom chip to monitor any attempt to write
to the area to be shadowed (in bank 00 or 01), then slow itself down to
1 MHz and write to the location and its equivalent in bank E0 or El
hexadecimal. In many locations (video display memory, for example) read
operations from the same location have no timing constraints and can
proceed at the higher 2.5-MHz speed. Because other locations (like the
ones associated with peripheral card I/O) must always be written to and
read from at 1 MHz, the speedup of Apple II software depends on the
memory locations the software uses.
Note that this scheme gets two things done. First, it allows existing
Apple II programs to write to bank 00 and 01 locations at the correct
speed and have the associated hardware perform the expected
interaction. Second, it allows programs to execute in the fast 2.5-MHz
memory, slowing down only at specific times.
By default, the Apple II GS shadows text page 1 in both banks, hi-res
pages 1 and 2 in bank 00, a 32K-byte area (2000 -9FFF hexadecimal) in
bank 01 used for the new super hi-res graphics modes, and the 4K-byte
section of memory at CXXX hexadecimal in bank 00. However, programs can
access a "shadow register" that can disable shadowing in individual
areas. This speeds up program execution and allows the program to use
the unshadowed areas and their EO/El (hexadecimal) counterparts for
other things.
(The bit that shadows the CXXX [hexadecimal] area also uses the actual
memory in locations C000-CFFF hexadecimal to hold the 4K-byte alternate
language-card areas for both banks. When this shadowing is turned off,
the language cards of banks 00 and 01 are no longer present, and the
65C816 sees a completely linear address space in banks 00 and 01.
[However, all Apple system software requires the CXXX shadowing to be
enabled.] The FPI chip controls shadowing and, in general, the
intercepting and translating of all the address requests from the
65C816.)
Slots and Ports
The II GS's expansion slots are iden tical in function and
configuration to the Apple IIe's slots with the exception of one added
signal, /M2SEL, which appears at pin 39, replacing the 6502 SYNC
signal. /M2SEL is an active-low signal that indicates when the II GS is
executing at slow speed (1 MHz) and the address lines A0-A1 5 are valid
(i.e., the II GS is talking to the slow RAM or I/O). In some ways, this
signal is redundant with the old IOSEL and DEVSEL signals in the
II+/IIe, and boards that use these signals should have no problem
operating in an Apple II GS. Control-signal generation and clock-signal
buffering on the ports are handled by the SlotMaker custom IC.
Associated with each I/O expansion slot are built-in circuits and
firmware that form an "invisible" port. The default settings for the
seven slots are
Slot 1 serial printer port Slot 2 serial modem port Slot 3 80-column
display Slot 4 mouse Slot 5 3-1/2-inch disk drives Slot 6 5-1/4-inch
disk drives Slot 7 AppleTalk
It is as though you ha d an Apple IIe with boards for all the above
devices already plugged in. Unfortunately, this wealth of built-in
interfaces carries with it some restrictions, the most severe being
that if you have an expansion board you want to run in your II GS, you
must give up the built-in port of whatever slot you plug the board
into. (You use the Control Panel to choose whether a slot is using its
associated default port or a plug-in board: this information is
retained in battery-backup RAM.) The serial ports of the Apple II GS
appear on the rear of the cabinet in the form of a pair of 8-pin
mini-DIN connectors. They are pin- and signal-compatible with the
serial connectors on the back of the Macintosh Plus--in fact, the USART
in the II GS is the same as the Macintosh's: a Zilog 8530 serial
communications chip. If you access the serial ports through the
firmware, they "appear" identical to the Apple Super Serial Card (SSC)
even though the SSC uses a different UART, a 6551. This has dire
consequences for software that tal ks directly to the serial-port
hardware on Apple IIs equipped with SSCs. Such software--and this
includes practically all of the commercial communication packages--
will certainly fail on the II GS.
Programs that bypassed the SSC's firmware did so to break the speed
limitations of the firmware's noninterrupt-driven, unbuffered I/O
routines, which were virtually useless for dependable communications at
1200 baud. The II GS's serial port firmware solves these troubles: It
is interrupt-driven, and each serial port has input and output buffers
that default to 2K bytes each but can be set to up to 64K bytes each.
The Apple II GS's built-in disk port is a 19-pin miniature D-type
connector in the middle rear of the machine. You can daisy-chain up to
four drives, up to two 3-1/2-inch drives followed by up to two
5-1/4-inch drives. Owners of Apple IIs who might want to use their
drives on the II GS can simply plug their Disk II controller into slot
5 or 6 and override the default setting for that slot.
Memory Expansion Slot
The Apple II GS motherboard has a special memory-expansion slot
designed for a card with up to 8 megabytes of RAM and 896K bytes of ROM
(bringing the system's total ROM to 1 megabyte). The RAM maps into
banks 02 to 7F hexadecimal, and the ROM maps into banks F0 to FD
hexadecimal. It is easiest to design 1- and 4-megabyte RAM cards (using
256K-bit by 1 chips and 1 megabit by 1 chips, respectively), but the II
GS engineers said that, with a few extra chips for interfacing, you
could design an 8-megabyte RAM card; however, since the machine is not
designed to hold user RAM above bank 7F hexadecimal, an 8-megabyte RAM
card would be unable to access the top two banks (128K bytes) of its
memory.
SmartPort
SmartPort is a set of assembly language routines (held in firmware) for
accessing block and (as yet undesigned) character I/O devices on the
Apple II GS. The SmartPort routines provide support for 3-1/2-inch disk
drives, a RAM memory disk (called the /RAM device), or a ROM memory
disk (5-1/2-inch drives, though part of the daisy chain, are controlled
by the Disk II firmware, and future hard disks can be designed to
respond to SmartPort routines without being part of the daisy chain).
SmartPort handles I/O in blocks of 512 bytes; since the routines permit
up to a 4-byte block number, SmartPort can manage devices with storage
capacities up to 2,199,023,255,552 bytes. SmartPort's basic functions
include get device status, reset a device, format a device, read a
block from a device, Write a block, and send control information.
Any I/O expansion card that adheres to SmartPort conventions will have
signature bytes at specific locations in its on-board ROM. The II GS's
firmware will hunt for and recognize these at boot-up time, just as
ProDOS currently does on the Apple II.
As its name implies, the ROM disk is the equivalent of a RAM disk
emulator in nonvolatile read-only memory. This could come in handy for
keeping frequently used programs like assemblers, compilers, or the
like on hand for rapid execution. The II GS memory space has eight
64K-byte banks set aside for ROM disk expansion, located just beneath
the firmware ROM in banks F0-F7 hexadecimal.
Desk Accessories and the Control Panel
You can think of a desk accessory as a mini-application that can be run
from within another program. Macintosh owners are already familiar with
desk accessories -- those utility programs from the menu bar that
appear when you click on the apple symbol. The II GS supports two types
of desk accessories (with a tip of the hat, perhaps, to Coca-Cola):
classic desk accessories (CDA) and new desk accessories (NDA). A
classic desk accessory can be activated only by a keypress. Classic
desk accessories can be run with older Apple II programs (such as
Appleworks) and new II GS programs. A new desk accessory runs in the II
GS's desktop environment and is available from a pull-down menu similar
to the Macintosh's desk-accessory menu.
One clas sic desk accessory is built into the II GS: the Control Panel.
You call up the Control Panel by simultaneously pressing
open-apple-Control-Escape, which presents you with a menu containing
the following system configuration options:
Display selects color or monochrome monitor, display width, and colors
for text, background, and border. Sound displays two "slider switches"
used to adjust the II GS speaker's, pitch and volume. Speed selects
1.0-MHz or 2.8-MHz ("normal" or "fast") operation of the 65C816 CPU.
Clock sets the II GS system clock time and date. Options alters
parameters of the II GS's keyboard: keyboard layout, keyboard buffering
on or off, repeat speed and delay, and others. Slots lets you indicate
for each of the II GS's seven I/O slots whether the slot is running an
"invisible" port or a plug-in board.
Other selections from the Control Panel let you set parameters for the
serial ports and enable a RAM disk. You can use the Control Panel from
within any program; we even used it in the middle of a disk access with
no adverse effects.
Video Modes and the VGC
Because the Apple II GS emulates the Apple II, it contains all the text
and graphics modes of the Apple II: 24 by 40 text, 24 by 80 text, 48 by
40 low-resolution and 48 by 80 medium-resolution graphics with 16
predefined colors, 192 by 140 hi-res graphics with 6 predefined colors,
and 192 by 140 double hi-res graphics with 16 predefined colors and 192
by 560 monochrome graphics. (Apple claims double the above numbers for
hi-res resolutions in the horizontal directions, but the numbers here
more accurately reflect the true nature of hi-res graphics because Of
the color limitations between adjacent pixels.)
As stated earlier, removing the banks E0 and E1 (hexadecimal) dynamic
RAM refreshing from the video display circuitry makes new video modes
possible. A new custom chip, the Video Graphics Controller (VGC),
implements both old and new video modes as well as unrela ted support
functions for the built-in clock chip, the disk drives. the interrupt
system and built-in chip and board testing routines. The VGC enhances
current text modes by allowing the user to choose from the Control
Panel the color (or gray scale value) of the text, its background, and
the border outside the active text/graphics area. These modes are
available only when using an RGB color or monochrome monitor.
Super Hi-Res Graphics
The new modes are called "super hi-res." Actually, there are three
modes that can be used in four ways; two of them are pretty
straightforward and useful, while the other two are more experimental.
Associated with the super hi-res modes is a 32K-byte chunk Of memory in
bank El ranging from addresses 2000 to 9FFF (assume that the addresses
in this section are hexadecimal and the quantities are decimal). The
pixel map occupies the range from 2000 to 9CFF, an important set of
pointers occupies locations 9D00 through 9DFF, and color palette
informatio n fills the remainder of the area, from 9E00 to 9FFF. (To
get into these modes, write C1 hexadecimal to location C029, and write
41 hexadecimal into it to restore the Apple II modes.)
The pixel map contains exactly 32,000 bytes arranged as 200 rows of 160
bytes each. Apple II programmers, who have always struggled with a
convoluted pixel-to-memory mapping scheme, will be surprised by the
fact that the super hi-res modes are completely linear, with a
row-first stream of pixels corresponding to an unbroken, increasing
progression of memory addresses. In other words, the first pixel on the
first line uses the high bits of location 2000, while the same pixel in
the second line uses location 20A0(160 bytes later), and so on.
There are two super hi-res modes. Both have 200 lines per screen, but
one has 320 pixels per line (see photo 2), while the other has 640
pixels per line. Since each line is represented by 160 bytes, each
pixel has 4 bits of memory in the 320 mode and 2 bits in the 640 mode
(see fig ure 3). This scheme gives you 16 colors in the 200 by 320 mode
and 4 colors in the 200 by 640 mode, with no restrictions on the color
of adjacent pixels (a problem that complicates the Apple II hi-res
modes).
With the old Apple II hi-res modes, the electronic characteristics of
both the Apple II and its video display determined the colors that were
available; for example, the hi-res mode gave you the colors violet,
blue, green, orange, black, and white. The Apple II GS, through the VGC
chip, gives you more control over the colors in your graphic display.
The super hi-res mode lets you choose your palette of 16 colors from a
color set of 4096.
But which of these 16 colors are used in the 640 by 200, 4-color mode?
The answer is all of them, the details of which lead us to one of the
experimental super hi-res modes. The two bits of a pixel in this mode
can have four values, so they are used in this mode to choose from 4
colors in the 16-color palette. Which 4 colors? Apple II programmers
will recogni ze the answer as yet another convoluted video mode in the
Apple II tradition: The 4 colors available for a pixel depend on its
position within a byte (see figure 3b).
Palettes and Pointers
Actually, the Apple II GS defines a 512-byte area starting at location
9E00 hexadecimal; this area contains 16 color palettes of 32 bytes
each, numbered from 0 to F hexadecimal. Each color in a palette is
defined in 2 bytes, using 4 bits each to describe the red, green, and
blue components of the color. The first byte contains the values for
green (bits 7-4) and blue (bits 3-0); the second byte contains the red
value (bits 3-0), with the remaining bits set to zeros.
Why are there 16 palettes? Because each scan line can use any of them
in any order. This brings the total number of colors that can appear
onscreen to 16 x 16 = 256 colors. Expect to see some uncharacteristic
graphics as soon as programmers learn their way around the machine.
The final surprise of the super hi-res graphics mo des comes from the
pointer area. The pointer byte at location 9D00 hexadecimal corresponds
to the top line of the video display, with each successive scan line
getting the next byte: 9D01, 9D02, ... , etc. This byte is read and
interpreted during the horizontal retrace of the previous video line.
Within each pointer byte, bits 3 through 0 determine which of the 16
color palettes is to be used. Bit 4 is not used and should be set to 0.
Bit 6 does nothing if set to 0. If it and an interrupt register at
address C023 hexadecimal are both set to 1, the VGC generates an
interrupt at the beginning of the line; this will allow the advanced
programmer to wring extra performance out of the super hi-res screen by
altering palette values (or making other useful changes) "on the
fly"--that is, while the machine is drawing the video display, Bit 7
determines the resolution: 0 for 320 pixels, 1 for 640.
This leaves bit 5, which does nothing if set to 0 but which activates
the final, experimental super hi-res mod e, called fill mode (see photo
2). In fill mode (which works in 200 by 320 resolution only), you have
access to 15 colors (numbers 1 through F, hexadecimal). A pixel value
of 0 means that its color is the same as the last nonzero pixel to the
left. In other words, pixels with the values
3 0 0 0 2 0 0 0 0 0 0 0 9 0 0 0
would appear as colors
3 3 3 3 2 2 2 2 2 2 2 2 9 9 9 9
and you could change the large area painted with color 2 to, say, color
5 by changing one pixel (the fifth one) from a 2 to a 5. (Note that the
first pixel in a line must always be nonzero.) This mode will be good
for drawing large areas and changing their colors very quickly.
Sound
The heart of the II GS's sound system is the Digital Oscillator Chip
manufactured by Ensoniq and used in the Mirage digital synthesizer. The
DOC is attached to its own personal bank of 64K memory into which
programs store wave tables that the DOC uses to generate sound. This
memory is accessible only through special registers in the Sound
General Logic Unit, a custom chip that acts as an interface between the
DOC and its memory and thus allows sound generation to proceed
independent of other processing in the Apple II GS. Additionally,
registers within the Sound GLU chip regulate the gain of the II GS's
audio amplifier, providing control of the speaker's volume.
The Ensoniq DOC contains 32 oscillators that the II GS firmware
operates in pairs to generate a tone. Since one of the oscillators is
used by the system to generate a time-slice interrupt for the DOC, the
Apple II GS can produce up to 15 independent tones simultaneously.
A wave table is a series of bytes in the DOC's memory such that each
byte represents the instantaneous value of the amplitude of the sound's
output waveform. An oscillator on the DOC will step through this table
fetching bytes and passing them to an on-chip digital-to-analog
converter that produces the analog waveform that, after filtering, goes
to the speaker. This technique allows generation of a theoretically
limitless range of sounds, bounded only by the amount of memory
available. The limit of 64K dedicated memory is no impediment, since
the II GS allows you to fill one portion of a wave table while the DOC
is fetching information out of another. The II GS passes the
unamplified monophonic signal of the sound system's output to a mini
stereo phone jack on the back panel of the machine. This output is
capable of driving a pair of Walkman-style headphones or, with the
proper adapter cable, the input of a stereo amplifier. The designers of
the II GS have also provided a connector on the motherboard that gives
direct access to several useful DOC signals, including an unfiltered
audio output, channel selection logic signals (can be used to implement
eight independent audio channels), and an input to the DOC's
analog-to-digital converter (for a sound sampler/digitizer).
The Apple II GS Toolbox
In the past, the Apple II could be almos t completely described by its
hardware features. The Apple II GS ends this tradition with its
inclusion of significant amounts of system software in both ROM and RAM
meant to be available to all programs. It is not accidental that these
routines are similar in name and function to those in the Macintosh
computer. The Mac toolbox is an elegant, powerful system proven to work
and improved by two years of intensive use.
The Apple II GS toolbox implements the most useful Macintosh toolbox
functions, though sometimes it does so in a different way; the Memory
Manager, for instance, works quite differently from its Macintosh
counterpart because of the way the Apple II GS's memory is divided into
64K-byte banks. However, the Apple II GS doesn't duplicate all of the
Macintosh toolbox.
The code in the Apple II GS toolbox is divided into tool sets , and the
individual routines are called tool calls . The tool sets that are in
ROM are the Tool Locator, Memory Manager, SANE (Standard Apple Nume
rics Environment) Numerics, Desk Accessory Manager, Event Manager,
Sound Manager, Integer Math Tools, Text Screen Tools, Scheduler, and
Miscellaneous Tools. QuickDraw II is divided between ROM and RAM.
The remaining tool sets are stored on disk and loaded into RAM by the
application that needs them. Once in memory. they are indistinguishable
from tools stored in ROM. They are the Menu Manager, Window Manager,
Control Manager, Line Editor, Dialog Manager, Scrap Manager, and Print
Manager.
Tool Set Structure
The Apple II GS tool set has no fixed routine entry points and only
four fixed addresses associated with its toolkits, yet any program can
execute any toolbox routine in RAM or ROM, even if a routine is changed
or moved to a different location after the program is written. Both
tool sets and tool calls are numbered (starting with 1), and any tool
call can be executed by the following assembly language sequence:
push inp1 |dx #CallID js| Dispatch
This pushes any input onto the stack, loads the 16-bit X register with
a call ID constant that has the tool call number in the high byte and
the tool set number in the low byte, and does a subroutine jump to a
fixed entry point. A high-level language would compile a normal
procedure call as a series of 0 or more push instructions, followed by
a jump to a different location that performs the above function while
handling an extra 3-byte return value on the stack. The Apple II GS
designers estimate that this type of call has an overhead of about 118
microseconds. Parameters can be passed in several ways, based on the
needs of the individual routine: on the stack, in a known block of
memory, or in the A, X, and Y registers.
To increase the usability and extensibility of the II GS, its designers
provided an identical but parallel structure that allows programmers to
build and use their own tool sets without "borrowing" tool set numbers
that Apple may later use. The only difference between the two is a
different entry point, "UDispatch" instead of "Dispatch."
Toolkit Memory Usage
Many tool calls need their own memory -- sometimes page zero locations
to speed up their execution, sometimes other memory for passing
parameters or sharing or storing data. The Apple II GS designers
resolved the conflicting memory needs of many different tool calls by
regulating memory usage as follows: The program using the tool sets
will itself allocate page zero memory. and tool sets will allocate the
other memory they need by asking for it through the Memory Manager.
They can then point to it with the WAPT (Work Area Pointer Table) entry
reserved for that tool set, and their tool calls will always be able to
access that memory in whatever way they wish.
QuickDraw II
QuickDraw II deserves mention because of its importance for
desktop-based Apple II GS software. It is a tool set, partly in ROM and
partly in RAM, that provides a standard set of useful graphics routines
for drawing window/ menu-oriented screens. Wherever possible and
appropriate, it attempts to work equivalently to a subset of Macintosh
QuickDraw routines. The pre-release documentation lists 146 QuickDraw
II tool calls, of which 114 are listed as being the same as their
Macintosh equivalents, 22 are listed as being similar, and 10 are
entirely different or absent. The degree of consistency between
QuickDraw and QuickDraw II will be very important to Macintosh software
developers attempting to convert their software to the Apple II GS.
ProDOS
Apple has crowned ProDOS the operating system for the Apple II series
of computers, and the company will be guiding ProDOS along a carefully
controlled development path that proceeds as follows: ProDOS 1.1.1 will
continue to be supported for the Apple IIe and IIc computers and many
ProDOS 1.1.1 programs will run on the II GS. ProDOS 8, an altered
version of ProDOS 1.1.1, will become the standard 8-bit operating
system for the Apple II. It will wor k on the IIe, IIc, and II GS.
ProDOS 16 will be the 16-bit operating system used for Apple II GS
software. Version 1.0, supplied with the machine at its introduction is
built on a ProDOS 16 framework but is implemented by a ProDOS 8 core
surrounded by a shell handling ProDOS 16-style calls. ProDOS 16 version
2.0 will be released in the first quarter of 1987.
The Finder
We did not see the Finder working when we saw the Apple II GS but its
preliminary documentation describes it as "a combination Program
Selector/Disk Utility for managing documents and directing traffic
between the user and storage devices." It seems to be a pretty faithful
imitation of the Macintosh desktop interface, with several exceptions.
First, the "Special" menu has two new items -- "Check Drives" and
"Format." The first causes the Finder to update its knowledge of what
disk is in each drive (remember that, in an Apple II system, you can
change the floppy disk in a drive without the computer knowing wha t
you've done). The second will eventually allow you to format a disk in
either ProDOS, Apple Pascal, DOS 3.3, or Apple CP/M formats; the
initial release, however, will only format disks for ProDOS.
Second, the Finder will interact most fully with ProDOS disks and
programs. Since only the ProDOS operating system has subdirectories,
only ProDOS disks will have folders in their windows. When you exit a
ProDOS program, it will return you to the Finder.
Third, the Finder does not support custom file icons. Each icon will
have a shape determined by its file type.
Finally, the Finder will support rudimentary printing of text files.
A future version of the Finder will probably add the Macintosh MFS
(old) and HFS (hierarchical) disk formats, Apple Pascal 1.3, and Apple
CP/M to the file types supported.
Apple Desktop Bus
The Apple Desktop Bus (ADB) is used for the generalized connection of
the computer with up to 16 input devices daisy-chained to a single
connector on the back panel: it currently supports multiple keyboards
(for educational and other programs) and a mouse (ending the daisy
chain), but the design can accommodate other kinds of devices. Devices
are connected through a shielded 3-conductor cable using mini-DIN-4
connectors.
The ADB is controlled by a dedicated 8-bit processor called the ADB
microcontroller (abbreviated here as ADBM); in addition, the mouse and
keyboard are controlled by custom microcontrollers that interact with
the ADBM. The ADBM and the intelligent devices "talk" on a bus where
only the ADBM can issue commands: the devices reply as appropriate with
data or requests for service.
In general, the ADBM handles low-level interaction with the keyboard,
mouse, and other input devices, thus freeing the 65C816 processor from
having to handle such tasks.
AppleTalk
Unlike any other Apple Computer product, the Apple II GS includes
built-in AppleTalk code in RAM and ROM. Through the Control Panel, you
can configure s lot 7 as AppleTalk; the II GS then uses one of the two
serial ports as its AppleTalk port.
The II GS implements the bottom two (of seven) levels of AppleTalk
protocol; Link Access Protocol (LAP) and Datagram Protocol (DDP).
Delivery protocol (DDP) also implements enough of the next two levels,
Name Binding Protocol (NBP) and AppleTalk Transaction Protocol (ATP),
to boot the II GS from a remote file server (thus allowing it to be
used in a network environment without its own disk drive).
Pricing
The price for the Apple II GS had not been set at the time of this
writing, but we expect the price for a starter system with one
3-1/2-inch disk drive and a monochrome monitor to be in the $1400 to
$1600 range.
Compatibility
For many users, especially current owners, software and hardware
compatibility will be the make-or-break factor in their decision to buy
an Apple II GS. The II GS engineers did an incredible job of designing
a new, more powerful computer th at is largely compatible with the
existing body of Apple II hardware and software. One engineer estimated
the II GS's hardware compatibility at "about 80 percent" and its
software compatibility at "95 to 99 percent."
Complete software compatibility is impossible, largely because of the
completely unregulated way the Apple II has been programmed in the last
10 years. People wrote code that jumped into the middle of ROM
routines, used machine language op codes that were unimplemented in the
6502 (but that are in the 65C816), and implemented countless
copyprotection schemes, many of which depended on particular hardware
details that were replaced in later Apple II designs.
The final verdict must wait until we get to test a production-line
machine, but we tested several Apple II game and business programs and
found two that fail trying to execute formerly unimplemented op codes
(THE Spreadsheet and Serpentine) and one (HomeWord running under ProDOS
1.1.1) that doesn't work because the 65C816 does not completely emulate
the way the 6502 wraps an X-register address from FFFF hexadecimal to
0000 (it wraps to 10000 hexadecimal).
Most peripheral cards that do not implement "phantom slots" (where a
multifunction card appears to be several cards in different slots) will
work, but some cards won't; we were told, for example, that the
Mountain Computer Music Card set won't work because of the way it uses
interrupts.
As with previous enhancements to the Apple II line, such differences
cause problems for the first year or so, then they fade from
consciousness as companies revise their products and users find patches
or workaround measures for products that don't work. In general, the
more recent your Apple II software or hardware, the more likely it is
to run properly.
Caveats
We wrote this product preview in July 1986, after two days with the
Apple II GS engineering staff, much study of seven volumes of
developers' technical documentation, and subsequent telephone
conversations with the engineers. When we saw the Apple II GS, the
firmware was about to be "frozen," and the machine itself was in "final
preproduction"; only minor changes are likely to be made at this point.
We did not get to see the Finder software, but we had several hours of
hands-on experience and ran several impressive sound and graphics
demos.
(We wish to thank Rob Moore, Harvey Lehtman, and many other Apple
people for their help.)
Conclusions
What do you say about such innovative energy that has been directed
primarily toward preserving a hardware design that is 10 years old? The
Apple II GS designers achievements are remarkable, but the burden of
the classic Apple II architecture, now as venerable (and outdated) as
COBOL and batch processing, may have weighted them down and denied them
any technological leaps beyond an exercise in miniaturization. Also,
the 65C816 may prove to be an IC of mixed blessings: While it does
provide a means of supporting the 6502 within a processor that also
operates in a 16-bit mode, to programmers it represents yet another
instruction set that has to be learned and whose oddities will have to
be dealt with.
The Apple II GS affirms several trends in microcomputer design that we
should not ignore: improved graphics and sound, larger processor and
memory capacity, and the use of a mouse and a desktop/icon/windows user
interface. The machine also follows a trend but breaks new ground in
the Apple II line by including large amounts of system firmware that is
as important as the machine's new hardware features.
Because Apple perceives itself as a "premium label," its pricing will
not be as aggressive as many users would like it to be. Apple is
becoming -- dare we say it? -- more and more like IBM, selling more on
name, reputation, and installed base of software and hardware (not a
strong selling point, in the case of Apple II software) than on
computing-power-per-dollar value.
The Apple II GS, hog-tied by Apple II compatibility, approaches but
does not match or exceed current microcomputer capabilities. The
8086-like segmented memory of the 65C816 is not as elegant as that of
the 68000, used in the Apple Macintosh, the Commodore Amiga, and the
Atari 520ST. In addition, the 65C816 lacks the hardware multiply and
divide instructions available in both the 8086 and the 68000
processors. The Apple II GS's graphics, though now competitive, do not
offer any advantages over the Amiga's or the Atari ST's, nor is its
price competitive with either. Its only clear superiority is in its
sound capabilities, which for many buy ers will not outweigh graphics
and price.
Ironically the Apple II GS will suffer from the traditional lack of
software and hardware upon its introduction. Vendors will take longer
than they expect to come out with new products, and many will enhance
existing products for the Apple II instead of writing new software that
fully exploits (and is limited to) the Apple II GS. Granted, a
tremendous amount of software is already out there, b ut the Apple IIe
and IIc will run it with fewer compatibility problems and at a
significantly lower cost. As with new machines before it, people will
buy the Apple II GS because they see the unrealized promise of its new
features.
October 1986 - Byte Magazine