Commodore-Amiga A500
From BozNet
The Commodore-Amiga came into official being in 1985, after a company that initially called itself Hi-Toro, and then thankfully changed its name to Amiga (Spanish for girlfriend), was bought by Commodore (who swiped it right under the noses of Atari, and more importantly, Jack Tramiel, who used to be Commodore's CEO). Commodore formed a sister company, Commodore-Amiga, to look after the Amiga range. The A1000 was the first model but didn't do very well, as it was priced higher than the Atari ST, which had really stolen Commodore's thunder. Commodore next came out with the much more successful A500, and in January 1990, Commodore had sold its 200,000th Amiga A500 in the UK. There were other models to follow, like the A1200, but the A500 was the most popular and best-selling of the range.
I got my Amiga 500 (most people miss off the "A" at the start of the model number), my fourth computer, in late 1988; and a mighty fine computer it was, too! After learning 6502 on the C64, learning 68000 on the Amiga was a breeze, and the Copper was an excellent idea to produce all sorts of graphic effects. The only downside, in a way, is the sound chip because it only supported samples (although chip-type sounds could have been pseudo-generated).
I managed to make a few demos, games and pieces of music on the Amiga, including a couple of public domain games with Mental Image.
In 1993, I sold my Amiga 500 and bought an Amiga 1200; I must say I was disappointed, especially because of the problems with a lot of the games that were made for the A500 and I wish I had kept it; but the Amiga itself was a lovely little machine with a solid operating system (and proper pre-emptive multitasking!).
Amiga Tech File
| CPU and Memory | At the heart of the A500 was the Motorola 68000 running at 7.16MHz; which was first released in 1979 and was the same chip used in the Atari ST and the first Apple MacIntosh. The A500 came with 512Kb of memory as standard, and an extra 512Kb could be slotted in the underbelly of the machine. Memory above this 1Mb could be also added on a slot in the left-hand side, and this was usually combined in a hard disk/memory unit. |
|---|---|
| The PAD | The biggest difference between the Amiga and the Atari ST was that the Amiga didn't rely on the CPU alone to do all the hard work, like the ST did; it had a set of custom chips called The PAD, which stands for Paula, Agnus and Denise, the three names given to the custom chips. These were all chips based on VLSI technology (Very Large Scale Integration), which means they had many more components (usually transistors) than usual, which were all highly specific to the task that the chip was built for. |
| Agnus | Agnus was the Big Boss of the Amiga; in fact, she was renamed Fat Agnus in the A500, after she was updated from her thinner sister in the A1000. Agnus was responsible for the Blitter, a contraction of Block Image Transferrer, which could transfer large chunks of memory at high speeds, draw up to 4000 lines every second and perform solid fills. Agnus and the Blitter, in unison, were also responsible for transferring data between computer memory and disk. The work was done via DMA so no processor time was used. Lastly, Agnus had Copper on board - a contraction for graphics co-processor - and was a small three-command coprocessor which could monitor and manipulate the screen while it was being drawn; this allowed split-screen displays and the like (similar to the Atari 800XL's ANTIC chip). |
| Denise | Denise's main task was to handle the main functions of graphic display. It converted bitplane information, held in memory, into a format that could be send to the monitor or tv screen. It also handled the mouse and controlled the 8 hardware sprites (which you could multiplex). Collision detection between sprite-to-sprite and sprite-to-background was Denise's job, too. On a "normal" graphic display, up to 32 colours out of a palette of 16 million could be used at once, but two special modes were also available: EHB (Extra Half-Brite), which doubled the chosen 32 colours and made them half as bright, effectively giving 64 colours; and HAM (Hold and Modify) which allowed the programmer to choose 16 "prime" colours, and then change the Red, Green and Blue values as each line was drawn, allowing an effective 4096 colours to be used. |
| Paula | Paula was responsible for the sound output of the Amiga, and was effectively a DAC (Digital to Analog Converter) and ADC. Sound on the Amiga was stored digitally, and played back through the DAC. The sound could be a ready-made wave, or made up on-the-fly (which was so called "chip" sound). Paula had four channels of sound; two connected to the left speaker and two to the right. Personally, this was a slight drawback in that you couldn't "position" the speakers in space, they were hard-coded, and listening in stero (especially using headphones) caused a painful stereo split. |
| Gary | Not featured as part of "The PAD" but still a custom Amiga chip, Gary is a contraction of "Gate Array," and handled the flow of data between interfaces and peripherals such as the bridgeboard. |
Related Links
Old Computers . com's entry of the Amiga 500; great repository.
http://uae.coresystems.de/: The Ubiquitous Amiga Emulator; originally started work on Un*x like systems, but now also available on other platforms, the Windows version's direct link being http://www.winuae.net/. An excellent all-round and solid emulator.
http://fellow.sourceforge.net/new_version/ is the link to WinFellow, a Windows version of "Fellow", another Amiga emulator. Just about as good as UAE, and a little faster in some areas as some of it is written in machine-language specifically for Windows. Try this if you come across a program that doesn't quite work in UAE.
http://www.amigaforever.com/ is the "official" one-stop shop for Amiga emulation. You can purchase a CD-ROM with an emulator, legitimate versions of Amiga ROM images, and programs. If you're an Amiga fan and want to donate to the cause (and stay legal), go right here.
http://www.aminet.net/, the largest repositories of (Public Domain) games, demos, applications and tunes.
