1. Disadvantage Of Absolute Loader

Disadvantage Of Absolute Loader

Data on tapes in the 'Absolute Format' is organized into blocks; each block begins witha 6-byte header:2-byte signature (0x0001)2-byte block length (N + 6, because it includes the 6-byte header)2-byte load addressfollowed by N data bytes. If N is zero, then the 2-byte load address is the exec address,unless the address is odd (usually 1). DEC's Absolute Loader jumps to the exec addressin former case, halts in the latter.All values are stored 'little endian' (low byte followed by high byte), just like thePDP-11's memory architecture.After the data bytes, there is a single checksum byte.

The 8-bit sum of all the bytes inthe block (including the header bytes and checksum byte) should be zero.ANOMALIES: Tape files don't always begin with a signature word, so I allow any number ofleading zeros before the first signature. Tape files don't always end cleanly either, so assoon as I see an invalid signature, I break out of the loop without signalling an error, aslong as at least ONE block was successfully processed.

In fact, it's possible that assoon as a block with ZERO data bytes is encountered, processing is supposed to stop, butI haven't examined enough tapes (or the Absolute Loader code) to know for sure.have referred to this tape format as the “Standard Absolute” format, but I’ve not found that terminologyused in any DEC publication. In fact, I think that term may have arisen from a misreading of instructionsfound in DEC manuals like the.

It should be discussed in detail. RecnoHere is the testdbf.prg source from hb30tests. It is a GPL piece of code poorly commented. LASTRECDELETE RECORD 4PACK? LASTRECIn this piece of code, the command DELETE marks the fourth record for deletion.