Editing LaserWriter (section)

===Legacy===
Apple's [[Raster image processor|RIP]] was of its own design, and was implemented using few ICs, including [[Programmable Array Logic|PAL]]s for most combinatorial logic; with the subsystem timing DRAM refreshing, and rasterization functions being implemented in very few medium-scale-integration PALs. Apple's competitors (i.e., [[Konica Minolta|QMS]], [[NEC]], and others) generally used a variation of one of Adobe's RIPs with their large quantity of small-scale-integration (i.e., [[Texas Instruments]]' 7400 series) ICs.

In the same time-frame as Apple's LaserWriter, Adobe was licensing the very same version of PostScript to Apple's potential competitors (Apple's PostScript licensing terms were non-exclusive); however, all non-Apple licensees of PostScript generally employed one of Adobe's PostScript "reference models" (Atlas, Redstone, etc.) and even [[Mergenthaler Linotype Company|Linotype]]'s first [[Linotronic|image setter]] which featured PostScript employed such a "reference model" (but with customization for the Linotronic's different video interface, plus the necessary implementation of "banding" and a hard drive frame buffer and font storage mechanism). Indeed, the PostScript language itself was concurrently enhanced and extended to support these high-resolution "banding" devices (as contrasted to the lower resolution "framing" devices, such as the LaserWriter, in which the entire "frame" could be contained within the available [[Random-access memory|RAM]]).

In most cases, such RAM was fixed in size and was soldered to the logic board. In late PostScript Level 1, and in early PostScript Level 2, the RAM size was made variable and was generally extensible, through plug-in SIMMs, beyond the 2.0 to 2.5 MB minimum (0.5 to 1.0 MB for instructions, depending upon PostScript version, and 1.5 MB minimum for the "frame buffer", for the lowest resolution devices, 300 dpi), as more than 300 dpi of course required more RAM, and some LaserWriters were able to change between 300 dpi and 600 dpi, depending upon how much RAM was installed. 600 dpi, for example, required 6 MB of RAM, but 8 MB of RAM was more commonly found.

At this point, Apple's LaserWriters were employing generic non-parity RAM, whereas HP's LaserJets, especially the ones which offered a plug-in PostScript interpreter card, required special parity-type PS/2 RAM modules with a "presence detect" function according to IBM specs.