1 CPU, Custom chips, RAM and other stuff

This chapter contains questions concerning the Amiga-Hardware.

1.1 What are the 68EC020 and the 68EC030?

Motorola, the company producing the 680x0 family offers crippled versions of their processors. They are a little bit cheaper than the originals, that’s why Commodore decided to build the 68EC020 into the A1200 and the 68EC030 into the A4000/030.

The difference between the 68020 and the 68EC020 is that the latter can address just 16Mb of memory. That’s why the A1200 cannot have more that 10 Mb RAM. In most cases you will not notice the difference.

This is not the case for the 68EC030: Many owners will notice that the 68030 has an MMU and the 68EC030 doesn’t have. There are some important programs depending on an MMU, for example Enforcer (a debugging utility), GigaMem (a program to emulate virtual memory) or all current Unix versions (@pxref{Unix}). Other Amigas than the A4000 and the A3000 need an additional processor card to run these.

Finally the 68LC040 is a 68040 without FPU. See section What’s an FPU?.

1.2 What’s an FPU?

The first 680x0 processors (upto 68030) could process integers only. Floating point operations had to be emulated by the software. An FPU is a chip (or part of a chip) that can process floating point operations, a mathematical coprocessor.

One separates three FPU types on the Amiga: The 68881, 68882 and the 68040’s internal FPU. The 68882 is up to 1.5 times faster than the 68881, because it is splitted in two parts: A conversion unit (the FPU’s are using an 80 bit format internally) and the arithmetic unit. The 68040’s internal FPU adds a pipeline, but misses the trigonometric instructions of the others. These are still emulated by the software, 68040.library for example.

Special programs (Raytracing, DTP, Mathematics, TeX) are offered in a special coprocessor version which are up to 50 times faster than the original versions.

Michael Kaiser (kaiser@ira.uka.de)

1.3 Can I use a 3.5" HD in my A1200?

Many people would prefer to use a 3.5" instead of the smaller 2.5" drives as the former are much cheaper. This is possible, but you need a special cable to connect the drive to your IDE controller. Additionally you should put some isolating material between the drive and the main board. Some people report termic problems but I did not notice anything.

Some dealers offer a set which contains the cable, isolating material and for about 20$. See the magazines for more information.

Thomas Schuh (thomas@stepout.tynet.sub.org)

If you are going to install an IDE-harddisk, regardless if 2.5" or 3.5", you should always consider that the it may not work flawlessly, if the drive and ROM-version have not been tested and approved by Commodore. Regarding the A1200, one should also remember that this Amiga has not been designed to hold 3.5" harddisk drives. The 2.5" drives, which are mainly thought for portable computers, may have some advantages (for example in power consumption, heat emission or shock resistance) that could pay off because of the small keyboard case of the A1200 and the limited power supply. With the larger 3.5" drives, ventilation inside the computer might also be disturbed. If it is necessary to remove some shielding inside the A1200 to make the drive fit inside, even radio interference may occur.

To sum it up: if 3.5" harddisk drives could really be used in the A1200 without any problems, you could be sure Commodore themselves wouldn’t have used the slightly more expensive 2.5" drives in the A1200-HD.

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