Abstract: The present invention provides a low-cost computer system which includes a single sharable block of memory that can be independently accessible as graphics memory or main store system memory without performance degradation. Because the “appetite” for main system memory (unlike that of a display memory) is difficult to satisfy, the memory can be addressed by reallocating an unused portion of a display memory for system memory use. Reallocation of the unused display memory alleviates any need to oversize the display memory, yet realizes the cost effectiveness of using readily available memory sizes. Further, reallocation of the graphics memory avoids any need to separately consider both the system memory and the display memory in accommodating worst case operational requirements. In accordance with additional embodiments, improved efficiency of operation can be achieved to enhance concurrency between plural banks of memory when expansion memory is included.

Abstract: A low-cost, moderate performance small computer system is provided by allowing a single sharable block of memory to be independently accessible as graphics or main store memory. Allocation of the memory is selected programmably, eliminating the need to have the maximum memory size for each block simultaneously. Performance penalties are minimized by dynamically allocating the memory bandwidth on demand rather than through fixed time slices. A reallocatable memory subsystem enables transparent transfer of memory function of a lower-performance memory such as DRAM to occur in conjunction with a memory upgrade to a higher-performance memory such as VRAM, for example.

Abstract: In a text mode of a display controller, for each character of the text, a plurality of multiple-byte words are stored in a memory buffer. Each multiple-byte word contains an ASCII character code for the character, font attribute information for the character and at least one font line for the character. For each character font line to be displayed on the monitor, a multiple byte word is read. The attribute information and a first character font line are extracted from the multiple byte word. The display controller then constructs a character scan line for the character based on the attribute information and the first character font line. The character scan line may then be displaying on the monitor.