to use as soon as the cards went through the reader. B6500 and B7500 The B6500 (delivery in 1969) and B7500 were the first computers in the only line of Burroughs systems to survive to the present day. While they were inspired by the B5000, they had a totally new architecture. Among the most important differences were The B6500 had variable length instructions with an 8-bit syllable instead of fixed length instructions with a 12-bit syllable. The B6500 had a 51-bit instead of a 48-bit word, and used 3 bits as a tag The B6500 had Symmetric Multiprocessing (SMP) The B6500 had a Saguaro stack The B6500 had paged arrays The B6500 had Display Registers, D1 thru D32 to allow nested subroutines to access variables in outer blocks. The B6500 used monolithic integrated circuits with magnetic thin-film memory. B6700 and B7700 Among other customers were all five New Zealand universities in 1971. B8500 The B8500 line derives from the D825, a military computer that was inspired by the B5000. The B8500 was designed in the 1960s as an attempt to merge the B5500 and the D825 designs. The system used monolithic integrated circuits with magnetic thin-film memory. The architecture employed a 48-bit word, stack, and descriptors like the B5500, but was not advertised as being upward-compatible. The B8500 could never be gotten to work reliably, and the project was canceled after 1970, never having delivered a completed system. History The central concept of virtual memory appeared in the designs of the Ferranti Atlas and the Rice Institute Computer, and the central concepts of descriptors and tagged architecture appeared in the design of the Rice Institute Computer in the late 1950s. However, even if those designs had a direct influence on Burroughs, the architectures of the B5000, B6500 and B8500 were very different from those of the Atlas and the Rice machine; they are also very different from each other. The first of the Burroughs large systems was the B5000. Designed in 1961, it was a second-generation computer using discrete transistor logic and magnetic-core memory, followed by the B5500 and B5700. The first machines to replace the B5000 architecture were the B6500 and B7500. The successor machines followed the hardware development trends to re-implement the architectures in new logic over the next 25 years, with the B6500, B7500, B6700, B7700, B6800, B7800, B5900, B7900 and finally the Burroughs A series. After