20260813

This is the first release under the z486 name. The CPU and MiSTer core were
previously named z386x and z386_MiSTer; the new names better reflect the core's
pipelined design, hardwired instruction paths, integrated x87 coprocessor, and
486-class performance.

This release includes:

• Experimental x87 floating-point support. It is not yet complete, but is
  sufficient to run Quake.
• Faster common x87 arithmetic and memory operations. Quake 1.0.6 now reaches
  6.6 FPS, up from 2.7 FPS with the initial implementation.
• CPU speed adjustment for software that cannot tolerate the full CPU
  speed.
• Compatible with ao486's sysctl.exe for CPU speed selection. This allows the
  0MHz Lemmings 1 image to run correctly in high-performance mode at the 30 MHz
  setting.
• A reorganized CPU implementation with clearer functional-unit ownership and
  updated z486 architecture documentation.

Installation

This release requires the included updated MiSTer binary, because the core
identity changed from Z386 to Z486.

Put the files in these locations:

• MiSTer in /media/fat, after backing up the existing file.
• z486_20260813.rbf in /media/fat/_Computer.
• boot0.rom, boot1.rom, and disk images in /media/fat/games/Z486.

Disk images previously stored in /media/fat/games/Z386 must be moved or
copied to /media/fat/games/Z486 for this release.