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Aucbvax.5124 fa.unix-wizards utzoo!decvax!ucbvax!unix-wizards Wed Nov 11 17:13:06 1981 tape sizes >From decvax!duke!unc!smb@Berkeley Wed Nov 11 16:06:48 1981 The minimum record size is used to distinguish between data and noise records. It *is* legal to have records shorter than that, but the drive is entitled to disregard them if any errors occur. (As an aside, I would note that IBM tape drives and controllers are *not* limited to 32K records; the actual limits are somewhat more complex. First, and probably most important, the operating system enforces a limit of just under 32K -- 32760 or some such. This applies only to folks who use the standard OS access methods. Anyone willing to do some fairly simple (if you ignore error recovery) "CCW"-level programming, i.e., pretty close to the nitty-gritty hardware level (this *is* permitted by OS) can get 64K records. By using somewhat more complex techniques, it is possible to read larger blocks than that; in fact, it's even possible to read arbitrarily large blocks by dynamically modifying the CCW chain. I'm not sure if this latter can be done under MVS -- the virtual memory version of OS/MT -- but it's certainly possible under the older MVT versions.)

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