To get the few old programs which still do not work with the Gold Card’s 1920K RAM running and to simulate a system with less RAM for debugging, RES_SIZE resets the system and adjusts the RAMTOP to the desired value.
If you use RES_SIZE 128, high density and extra density disks cannot be accessed until the next reset. Secondly, the realtime clock runs by default in protected mode. Thirdly, the ramdisks cannot be accessed by the system. This should simulate the unexpanded, original QL. Normal disk drives (DD) can still be accessed, although this can be temperamental.
RES_SIZE 640 RES_SIZE 128 RES_SIZE 1024
You may find that some programs will still not work following RES_SIZE, especially if they use a line such as:
This appears to happen because RESPR(0) returns the address of RAMTOP which is still over 2MB even though only 128K is available. Minerva users should use:
At least up to Gold Card’s firmware v2.28, RES_SIZE does not check the range of the supplied parameter. If values lower than 56 or higher than 1920 are used, this can lead to crashes of a particularly serious character. Either the QL hangs during or after the resets, or there will not be enough free memory to enter any commands.
There is even a danger that a fatal crash will occur which can destroy data on hard disks, disks or microdrive cartridges, or the realtime clock can be affected or even combinations of these different crashes can occur. As hard disk drives cannot be removed or protected from any malfunction of the operating system or programs, they are in extreme danger.
It is also not advisable to use values other than multiples of 64 because software tends to expect a ramtop which is a multiple of 64 and memory is wasted.
RES_128 is identical to RES_SIZE 128. See also RESET. See RAMTOP and FREE_MEM about available and free memory. FLP_EXT improves the reliability of the floppy disk drives and allows RAM disks to be used.