Reply 40 of 46, by mkarcher
Horun wrote on 2022-09-12, 03:43:So in laymans terms the card is not a caching controller but a VLB multi I/O IDE HD controller with XMS/EMS capability ?
To allow EMS/XMS as valid description, we have to make gratitious use of "layman terms". EMS and XMS describe two particular ways for software to interact with the memory hardware. In the case of EMS, there is a hardware-specific driver that gets software requests to select certain areas of memory and programs the hardware accordingly. For XMS, there is basically just one driver, HIMEM.SYS, which is hardware-independent, because all memory boards that provide memory to be used using the XMS programming interface implement the same hardware interface called "extended memory". The XMS specification is written in a way that it is basically impossible to implement XMS with hardware that doesn't provide the memory as "extended memory".
The VL-200 does not implement the "extended memory" hardware interface, so it can't be used to provide memory to XMS application. Also, the VL-200 can not perform the operations in hardware that software could request using the EMS programming interface, so it also can't be directly utilized by software that requires EMS.
Nevertheless, in the grand scheme, the VL-200 (and VL-230) do provide extra RAM to the computer that can not be directly accessed by real-mode DOS applications. In that way, it is similar to EMS and XMS, which also can not be directly accessed from the processor in real mode. (I don't go into details (like the HMA) on purpose).