Hardware Emulation

This chapter includes the following sections:

• Emulated Components
• Performance
• Hard Disks
• Floppy Disks

Emulated Components

When you launch the Amiga OS 3.X environment, you are running an emulated Amiga featuring a CPU with a 68020 instruction set (with a performance that can exceed that of a 68060), a floating point unit (FPU), virtual memory (provided by the host operating system, e.g. Windows or Linux), TCP/IP (the Amiga shares an IP address with the host), a true color display card ("uaegfx") with Picasso96 drivers, a stereo sound card (AHI), and two SCSI devices (uaescsi.device for CD-ROMs, uaehf.device for other devices).

The Amiga custom chips are also emulated, providing, among other features, original Amiga screen mode and sound functionality, as required by popular Classic Amiga applications.

Similarly, when running the 1.3 environment (or other Amiga OS versions), the emulation makes available a slightly different virtual computer, with a 68000 CPU, a different amount of memory, no RTG or AHI, etc.

Within Amiga Forever, emulation of the Amiga hardware is provided by the different versions of the UAE and Fellow emulation engines which are preinstalled and preconfigured to use the Amiga ROM, OS and application software files that are part of Amiga Forever.

Performance

A frequent question is "Why does the emulation emulate a 68020 instead of a 68060 CPU?", where the implied question is about the speed of the emulation. Changing the emulated CPU, for example from 68000 to 68010 or to 68020 does not affect the emulation speed, but only the instruction set and addressing modes supported by the CPU. The 68030, 68040 and 68060 CPUs were designed with 68020 instruction-set compatibility in mind, and there are practically no Amiga programs which do not run on either the 68000 or the 68020. Most Amiga programs run fine on the basic 68000 CPU, while a few are compiled for the 68020 instruction set. The speed of the emulated CPU, regardless of the selected CPU type, is determined only by the power of the PC's CPU(s). On a sufficiently powerful computer, the emulated "68020" CPU can be several times faster than a silicon-based 68060 CPU, especially when the JIT option of the emulation is enabled (as it is by default in the 3.X configuration).

On slower systems, where the custom chips are not emulated in real time, different adjustments of the emulation settings may help run some games or other programs which require a lot of custom chip functionality. The performance of the emulation can be tuned by changing the priority of the CPU with respect to the Amiga custom chips. The emulation runs faster when a Picasso96 screen mode is selected, because in this case most of the graphics processing can be moved from the (emulated) Amiga custom chips to the Windows graphics hardware. To improve performance, the screen-refresh rate can be set to every second or third frame, instead of every frame. Disabling sound also improves performance, but a few programs do not work properly unless sound emulation is enabled, or sound output is disabled in those programs.

For additional information on this topic please refer to the FAQ section at the Amiga Forever Home Page.

Hard Disks

Like on the original silicon-based Amiga computers, the "System" volume contains Amiga system files, while "Work" is used to store application software and data files.

The "System" and "Work" volumes are mapped to directories on the PC filing system, of which they mirror the exact contents (select the "Window/Show/All Files" Workbench menu item to view files which do not have an Amiga icon file). After installation on a Windows system, these directories are usually located following a path like

• C:\Program Files\Cloanto\Amiga Forever\Emulation\shared\dir\System

and

• C:\Program Files\Cloanto\Amiga Forever\Emulation\shared\dir\Work

This means that the items contained in the "System" and "Work" directories appear as if they were contained in hard disks having the same name when viewed from within the emulation, but they can also be accessed from the Windows side. This is especially useful, for example, to copy software and data from a "real" Amiga to the emulation environment using the Amiga Explorer networking software, which is part of Amiga Forever.

For additional information on this topic please refer to the FAQ section at the Amiga Forever Home Page.

Floppy Disks

Amiga Floppy disks cannot be read by standard PC hardware, and are therefore stored and distributed as disk images, usually in "ADF" files. Several web sites (also listed in the Download section) make ADF files containing old Amiga games and other programs available for download, with permission from the former publishers.

Booting the Amiga from an ADF disk image is very easy: if you are already running the emulation (as you probably are if you are reading this text now) press F12 to open the emulation user interface, go to the Floppies tab, select one or more ADF disk images to insert, click OK, then reboot the Amiga by pressing Ctrl+Left Amiga+Right Amiga (check out this section for more keyboard shortcuts). If instead you are launching the emulation software via the configuration dialog you don't even need to reboot the Amiga, as it will boot directly from the chosen disk image.

The Amiga Explorer software can be used to create ADF files on the fly, so that existing Amiga floppy disks can easily be transferred to the PC, and vice versa.

Amiga Forever includes an experimental version of Vincent Joguin's "Disk2FDI" software, which, by adding an inexpensive second floppy drive to the PC, makes it possible to read most Amiga disks. The software and the release notes are located in the "Emulation\shared\dos_utilities" directory of the Amiga Forever installation (select "Browse Directory" in the Amiga Forever launcher).

For additional information on this topic please refer to the FAQ section at the Amiga Forever Home Page.