Some Key Amiga and Amiga Monitor-oriented links:
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Compiled by Greg Noggle, Telecommunications Editor and Hardware Guru, g.noggle@genie.com
DEVICE - Anything you can send and/or receive information to/from such as disk drives, modems, printers, CD-ROM drives, digitizers, etc. Even the screen is considered a DEVICE, as is the keyboard. We will look at the most used devices later.
MEMORY - An area where the computer stores information. Some of it is available to you to use; some of it is for the computer only. Every computer (and nearly every modern day electronic device such as wrist watches and microwave ovens) has at least SOME memory. There are MANY different types on some systems; the Amiga is one of them.
ROM - Read Only Memory. This is memory that can only be read from but not written to. The actual computer operating system (called Kickstart since it is actually required to 'start' your system) is contained on a replaceable chip inside the computer. This ROM contains permanent information the system needs to run.
RAM - Random Access Memory. Memory that you can load programs, graphics, and sound into for the computer to use. It is volatile, which means that when the computer is shut off (or rebooted using CTRL-LEFT AMIGA-RIGHT AMIGA) this memory is reset and (most of the time) lost. There are some ways around that which we will look at later when we talk about viruses. There are several types of RAM used in the Amiga, each one with a different purpose.
RAM (Fast) - Fast RAM is used to store programs used by the
central processor (the heart of the computer: a Motorola 68000
series microprocessor). In most early Amigas this is often 16-bit memory (more on
that later) since the 68000 is a 16-bit processor.
If your machine is equipped with an accelerator (68020, 68030, or
68040 CPU) then you have a 32-bit processor which runs
considerably faster that the 68000. This CPU requires
(obviously) 32-bit Fast RAM to run at its optimum performance.
If you only have 16-bit Fast RAM and a 32-bit processor, your
machine may not seem as fast as it should, since the processor
cannot operate at the speeds you paid for. 16-bit Fast RAM is
occasionally called SLOW RAM. You can put up to eight megs on a
processor with a 24-bit address register, such as the 16-bit 68000, (with some exceptions) and for all
practical purposes, pretty much unlimited (based on the weight of your pocketbook) on a 32-bit
processor.
This RAM can usually be added by sticking in a board or plugging
in a box on the computer. In any event, the custom chips (more
on that later) cannot use any form of FAST RAM for storage.
RAM (Chip) - Since the Amiga is a true multitasking
machine, it has several custom processors (called the CUSTOM
CHIPSET) to handle almost every function of the computer, leaving
the CPU free to do the basic number crunching and program
execution. These custom processors require their own memory in which to
store their own programs. The memory they are designed to use
is called (appropriately enough) Chip RAM. In older Amigas it
was set at 512K (one half a megabyte). Then, a modification came
out to let you have one megabyte of Chip RAM. The latest Amigas
have two megs of Chip RAM. Since all the graphics and sound are
stored here, it is easy to see why 'the more the merrier' is
quite true when it comes to Chip RAM. Chip RAM *CAN* be used by
the CPU if no Fast RAM is available. But, this is not desired
since Chip RAM is about 20% slower than the 16-bit Fast RAM.
Chip RAM is very costly and difficult to add. It also has a
little flaw in it called FRAGMENTATION. More on that later on.
DISK - A disk device (or drive) comes in many forms with
lots of different names. All drives require a CONTROLLER to talk
between them and the computer. The disk drive that is built into all Amigas is a 3.5" Floppy disk
drive. Note: although the
3.5" disk casing is hard plastic, the actual media inside the
casing is floppy so it is still considered a floppy disk. The
computer has a built in floppy drive controller that will allow
up to four floppy drives to be connected and accessed at one
time. Hard Disk Drives actually use rigid plastic disks to store
data. These are hermetically sealed inside the case and you
will probably never see what a platter (the disk itself) actually
looks like. They hold a great deal more than their floppy
counterparts and also require a controller to operate. Older
Amigas do not have this controller built in so it must be
purchased with the drive to use. A CD-ROM drive works the same
way, basically. It also requires a controller but stores its
information in little pits on the disc. These pits are of
different depths which represent numbers that the computer can
actually change into a program to run.
All controlled devices need a software program 'patch' or device
file to allow them to talk from the controller to the computer.
These are located in your DEVS: directory on your Workbench Disk or
hard drive partition. Floppy drives are denoted as DF0 - DF3 and hard
drives are usually denoted as DH0 - DH?. The Amiga internal disk
drives are all double density (with the exception of the A4000)
and hold 880K of data when formatted. There are some utilities
out there that will allow you to increase this number to 936K or
so.
RAM DISK - This is a special device. It allocates your memory as a 'mini disk drive' to allow temporary storage of files and data. On your Workbench, you should see an icon that says RAM DISK or RAM. This is just like a disk drive and you can copy to, delete from, install programs to, and manipulate it just like the disk drive counterparts. Its capacity is limited to your total available memory (displayed on the title bar of your Workbench disk). It does not need to be 'formatted' to be used. It is ready as soon as you see its icon. WARNING! It uses RAM to hold what is in it so if you reset your computer, crash it, a power failure occurs, etc. anything there will be LOST! There is a device you can create called a RAD, which is like a RAM DISK, but will survive anything but turning the computer off (or power loss). You can crash it, reset it, etc. and it will still be there when your Workbench loads. (Editor's note: if a program actually causing a crash overwrites data in RAD: on the way to the great guru in the sky, that information can be lost, but this is fairly uncommon)
PRT - Printer device. You can specify which device to send a file to in most Amiga programs. For instance, if you are working on a database and you want to save it to the internal floppy drive, you might enter a filename called DF0:DATABASE. With the Amiga, you can send it right to the printer! Simply enter PRT:DATABASE and it will send the file to your printer! Since you set your printer type in the PREFs (more later), all programs can make use of the special features of that printer.
SER - Serial device. This is the device that lets you talk to the serial port (used mostly by modems and printers). Like the PRT device you just need to use SER as the device name.
PAR - Parallel device. Talks to the parallel port. This is the most common port used by printers. Unless you are talking to another Amiga via a Parnet cable, the PRT would be better to use if you want to send something to the printer.
CON - Console device. The computer itself! If you send a file to the console device, it will display on your screen using your CON: device parameters.
If a lot of this doesn't make sense right now; be patient. Rome wasn't built in a day; nor was your Amiga. Give yourself some time to learn.
In the first Amiga, the A1000, the chips "Agnus," "Paula," and "Denise" did the hard work. They together build a specialized multiprocessor system that takes much of the time-critical load off of the main processor. This includes the plain display of image information, 4-channel sound output, floppy control, general DMA control, and much more. In the newest Amigas you find the "AGA chipset", which consists of the original "Paula" and the advanced chips named "Alice" (the replacement for Agnus) and "Lisa" (the replacement for Denise).
Over the years, the chipset was redesigned several times. The first chipset in the Amiga 1000 is called the OCS, for Original Chip Set. It consists of the chips Paula, Agnus, and Denise. With these, you can display graphics in resolutions up to 640x512 (or 640x400, depending on whether you had the American or European version) and in up to 4096 colors, a fantastic achievement in 1985.
The next generation was ECS, the Enhanced Chip Set. The chip names remained unchanged, except some minor additions like "Fat Agnus". Only Agnus and Denise were changed. Compared to OCS, they provided higher resolutions, but no expansion of the color palette so far. The current generation was created in the labs as the AA chipset (for Advanced Amiga), but in some countries it was later marketed as AGA (Advanced Graphics Architecture). Agnus was replaced by Alice and Denise by Lisa. The resolutions now reach up to 1280x512 in VGA scan frequencies. The color palette is now 24 bits or 16.8 million colors. You can display up to 256 colors simultaneously or in HAM mode more than 640,000. Backwards compatibility with Video and OCS modes is assured.
Copper is the short name for a "Coprocessor" which is integrated into the Amiga custom chips. It makes fast action games possible, as well as unbelievable color effects, and the capability to drag down a screen partially on the Amiga's display and thus show several screens at once. Technically, the Copper is a highly specialized microprocessor which knows only three different commands, but can process these extremely fast and efficiently. It provides the ability to change, for instance, graphics mode, color values, or sprite definitions somewhere at a well defined location within the screen. This way the Amiga can display many different actions on one screen simultaneously without activity by the main CPU.
Blitter is the short name for another graphics coprocessor which is part of the Amiga custom chips. With it you can copy rectangular image parts extremely fast to other areas. During this, you can take up to three source data areas and perform logical operations on them. This allows you, for example, to define certain color values of the copied object as transparent, thus not modifying the destination area. As an add-on, the Blitter can also draw lines and fill areas quickly. All in all it serves to provide extremely fast, animated graphics that can be designed to be especially realistic.
The HAM mode is one of several graphics modes that was provided by the Amiga custom chips from the start. With HAM, you can display many colors simultaneously while using up very little memory. Simply put, it's sort of a hardware data compression method by a factor of three. Still you can display practically all colors of the palette on screen.
Technically it works like the name says: HAM = Hold And Modify. Like other graphics modes, you have a palette with base colors, so that for every pixel you can store the number of its color in the video RAM. With the old HAM6 mode, these are 16 colors (4 bits per pixel); with the new HAM8 mode (since the AGA chipset), these are 64 colors (6 bits per pixel). Now in the video RAM two more bits of storage are provided, in addition to these 4 or 6 bits, for every pixel. This yields six bits for HAM6 and eight bits for HAM8.
These additional two control bits can assume four different states: In one state, the other bits give the number of a palette color like a normal graphics mode. In the other three cases, one of the three color components R, G, or B gets set to a new value from the other bits. This way this color component gets modified, while the other color components remain unaltered from the previous pixel, so they are held. This explains the name HAM.
This modification of one color component serves to render soft color transitions very accurately, as they are typical for natural pictures like portraits. In the HAM8 mode you can theoretically display more than 640,000 colors simultaneously on screen. The dependence on previous pixel contents sets certain limits, so that the HAM mode is less suited for realtime action. But in still pictures or precalculated animations, it lives with its many colors. With its data compression, the HAM mode is also responsible for the Amiga being so famous for its animations that can run at full speed, even on smaller Amiga models.
Basically you can display all 16.8 million colors of the 24-bit palette in HAM8 mode. But there are two limitations: for one, no current monitor (or screenmode) can display so many pixels simultaneously. In the screenmode SuperHiRes PAL Interlaced, there are e.g. 640,000 pixels. Second, it's not so easy to reach this color resolution with real-world pictures. Through the normal HAM8 mechanism you can only set the upper six bits of each color component red, green, and blue. Each component has 8 bit resolution so that we get a total resolution of 3 * 8 or 24 bit. The lowest two bits are only reachable through a special method, in that you have to choose the 64 base colors appropriately so that they exactly cover all 64 possible combinations of the lower two bits of all color components (3 * 2 bit = 6 bit, which gives 64 combinations). But for real-world pictures, you want to use the HAM mechanism to get smooth color transitions, so that the change to another base color is not preferable.
To summarize, you can theoretically (and in very special applications like demos) set practically every pixel on screen to a different color. But in reality you are limited to an 18-bit color space (18-bit from 3 * 6 bit of the HAM parts of the color components). In data sheets, you often find the theoretical maximum value of about 640,000 colors (limited by the number of pixels displayable on one screen).
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