When I boot, it tells me I have 640k of RAM, but Chkdsk says I only have 576k. What gives?
All of the 1000-series except for the 1000RLX’s and RSX’s have special video controller circuitry that allocates some of the video memory for DOS if there is less than 640k of conventional RAM installed. The video controller has 128k or 256k (depending on the model), which is more than it really needs under most circumstances, since CGA programs only use 16k, and even most programs that use the special Tandy video modes only use 32k (Hercules mono graphics also requires 32k). About the most that is ever used is the 64k that the special 640x200x16 video mode on the 1000SL’s, TL’s, and RL’s requires. (All video RAM could conceivably be used by some programs for animation.) The original 1000 was a clone of the IBM PCjr (see section IV.H.). The PCjr came with 128k RAM that was both video RAM and system RAM – whence the 128k attached to the video controller. Among other things, this enabled IBM to leave out the DMA controller the IBM PC had, since the RAM was continually being refreshed by
