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See BLT.

(I may need to look this one up -- I have a pretty good general idea, but maybe I should learn some specifics.)

block transfer: I think there are probably a few different meanings I should discuss.

One definition of a block transfer is a transfer of multiple bytes (or words or registers) of data under the control of a single software instruction. The instruction needs to know how many bytes of data to transfer, the address of the first byte of the source and the destination, and it has enough "guts" to transfer the whole block of data without additional instructions. (This sort of comes from the idea of a block transfer within a computer, from one location in memory to another, or from one device to another (a hard drive to a destination in memory). Sometimes such block transfer instructions are "really" one logical instruction in the firmware (but consisting of multiple subinstructions). Other times, a block transfer routine may be created at a higher level, by writing a subroutine in a programming language. In either case, the block transfer may be (is usually) smart enough to call for more help or at least indicate an error if something goes wrong.

Then there is the idea of (I think) a block transfer from one computer to another. Oops, maybe I'm about to confuse, for example, data transfer over a serial link vs. data transfer over a parallel link with block transfer -- I guess a modem (or its driving software) can be programmed to do a block transfer (of many bytes) even though each bit is transmitted (and received) separately. Likewise, multiple bytes of data can be transmitted over a parallel link, even though one byte (or group of bytes, or maybe better, one group of bits) is transmitted at a time. I guess I won't go any further in this discussion -- this may be appropriate for some other discussion.

Maybe a good way of looking at a block transfer is something like a transfer that uses software (or hardware) to automatically transfer a block of data larger than the interface being discussed can normally transfer at once, by breaking a block of data down to the size that can be handled at once and then continuing to transmit that amount of data time after time until the entire block is transferred.

(I think my definition demonstrates that I have a handle on the meaning (thus making me feel good) and can get the idea across to others, but probably should be simplified to use some more common terminology that is more compact.)

Aside: Is synchronous and asynchronous data transfer relevant here? Not quite, I don't think, that's a different subject, although perhaps block transfers may tend to be synchronous (??). Maybe not, that's not a good distinction. A block tranfer can be done over a modem, and modems / serial lines are ususally (I think) considered to be asyncronous. (Ignoring things like SDLCs(??), I think.)

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  • RandyKramer - 14 Jan 2002
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