Block-oriented Magnetic Tape Drives

The Ferranti Atlas (1962) had block addressable magnetic tapes: "The tape mechanism used on Atlas is the Ampex TM2 (improved FR 300) using one inch wide magnetic tape. There are sixteen tracks across the tape - twelve information tracks, two clock tracks, and two tracks used for reference purposes. The tapes are used in a fixed-block, pre-addressed mode. Information is stored on tape in blocks of 512 forty-eight bit words, together with a twenty-four bit checksum with end around carry. Each block is preceded by a block address and block marker and terminated by a block marker; the leading block address is sequential along the tape, and what is effectively the trailing block address is always zero. Tapes are tested and pre-addressed by special routines before being put into use, and the fixed position of the addresses permits selective overwriting and simple omission of faulty patches on the tape. Blocks can be read when the tape is moving either in the forward or reverse direction, but writing is only possible when the tape is moving forward. The double read and write head is used to check read when writing on the tape. When not operating the tape stops with the read head midway between blocks." Quoted from The Atlas Supervisor T Kilburn, R B Payne, D J Howarth 1962 Of course, these drives and media are likely to be even harder to obtain (to say the least!) than DECtape :) While on the subject of Atlas and referencing another thread on this list it would be a /real/ challenge to implement on an FPGA - Not for the lack of circuit diagrams (I understand several copies still exist) Not for the use of "wired-or" (don't know if Atlas used this logic technique, but several later Ferranti machines did) But because it used asynchronous logic which is contrary to the design philosophy of FPGAs (and almost all other modern logic for that matter) Andy