Base memory refers to the first 640 KB of memory and has its origins in the early IBM PCs (the IBM Personal Computer XT introduced in the early 1980s was expandable up to 640 KB). Base memory is used to store an Interrupt Vector Table, ROM BIOS tables, DOS, device drivers, TSRs (programmes that load into memory and stay there, for example calendars or spell checkers called by 'hot keys'). The first 64 KB of base memory is as it says: the first 64 KB block of base memory. Base memory problems are RAM problems.