two "control" bits per pixel, but with six bits of data per pixel instead of four. The set operation selects from a palette of 64 colors instead of 16. The modify operation modifies the six most significant bits of either the red, green or blue color component - the two least significant bits of the color cannot be altered by this operation and remain as set by the most recent set operation. Compared to HAM6, HAM8 can display many more on-screen colors. The maximum number of on-screen colors using HAM8 was widely reported to be 262,144 colors (18-bit RGB color space). In fact, the maximum number of unique on-screen colors can be greater than 262,144, depending on the two least significant bits of each color component in the 64 color palette. In theory, all 16.7 million colors could be displayed with a large enough screen and an appropriate base palette, but in practice the limitations in achieving full precision mean that the two least significant bits are typically ignored. In general, the perceived HAM8 color depth is roughly equivalent to a high color display. The vertical display resolutions for HAM8 are the same as for HAM6. The horizontal resolution can be 320 (360 with overscan) as before, doubled to 640 (720 with overscan) or even quadrupled to 1280 pixels (1440 with overscan). The AGA chipset also introduced even higher resolutions for the traditional planar display modes. The total number of pixels in a HAM8 image cannot exceed 829,440 (1440×576) using PAL modes but can exceed 1,310,720 (1280×1024) using third-party display hardware (Indivision AGA flicker-fixer). Like the original HAM mode, a HAM8 screen cannot display any arbitrary color at any arbitrary position, since every pixel relies on either a limited palette or relies on up to two color components of the previous pixel. As with the original HAM mode, designers may also choose to 'slice' the display (see below) in order to circumvent some of these restrictions. A HAM7 mode is also available but not widely used. HAM emulation HAM is unique to the Amiga and its distinct chipsets. To allow direct rendering of legacy images encoded in HAM format software-based HAM emulators have been developed which do not require the original display hardware. Pre-4.0 versions of AmigaOS can use HAM mode in the presence of the native Amiga chipset. AmigaOS 4.0 and up, designed for radically different hardware, provides HAM