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http://www.engr.iupui.edu/~skoskie/ECE362/lecture_notes/LNB25_html/text12.html says

There are many serial data transfer protocols. The protocols for serial data transfer can be grouped into two types: synchronous and asynchronous. For synchronous data transfer, both the sender and receiver access the data according to the same clock. Therefore, a special line for the clock signal is required. A master (or one of the senders) should provide the clock signal to all the receivers in the synchronous data transfer.

Does "serial data transfer" mean the same as sequential access, as opposed to random access?

Do both synchronous and asynchronous data transfer imply sequential access, not random access?

Can random access be either synchronous or asynchronous? Same for sequential access?

Thanks.

Tim
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1 Answers1

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Does "serial data transfer" mean the same as sequential access, as opposed to random access?

No, “serial data transfer” refers to serial communication, i.e. communication which happens one bit at a time. This is concerned with how data is transmitted over wires, not with what the data is.

Serial data transfer is contrasted with parallel data transfer; it’s orthogonal to sequential v. random access concerns, at a different level. It’s similar to serial v. parallel ATA: both are ways to send data to and from disks, but the data that’s sent can correspond to sequential or random accesses.

Do both synchronous and asynchronous data transfer imply sequential access, not random access?

Synchronous v. asynchronous transfers are properties of serial protocols, and refer to clock synchronisation. Again, this is considered at a different level compared to sequential v. random accesses. The transfers themselves are inherently sequential, but that doesn’t limit the types of high-level accesses which can be performed using serial transfers.

Can random access be either synchronous or asynchronous? Same for sequential access?

Again, these are orthogonal concepts. Synchronicity here is a specific concept related to signal transfer and clock synchronisation over wires.

Stephen Kitt
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  • Thanks. (1) "Synchronous v. asynchronous transfers are properties of serial protocols". Are they also properties of parallel data transfer protocols? (2) Do you mean serial/parallel data transfer is at a lower level than sequential/random access? (3) Are block/character devices at a higher level than sequential/random access? – Tim Oct 02 '18 at 16:53
  • (4) What kinds of users of devices should see which level but not the levels under the level? For example, what level(s) should a user of Linux or a programmer using Linux API can be aware of, and not aware of? – Tim Oct 02 '18 at 16:53
  • (1) Theoretically yet, but in practice the majority of parallel protocols are synchronous. (2) It’s not really a question of levels, they’re orthogonal issues. (3) See (2). (4) When you’re writing programs on Linux, you might care about sequential v. random, but you’re unlikely to care about serial v. parallel; that’s a concern for people writing device drivers or building hardware. – Stephen Kitt Oct 04 '18 at 15:04
  • Thanks. "Synchronous v. asynchronous transfers are properties of serial protocols" (as in your reply) or parallel protocols (as in comment), serial ports and parallel ports are both character devices, and character device almost always implies sequential access. So do Synchronous and asynchronous transfers almost always imply sequential access? – Tim Oct 05 '18 at 03:58
  • You shouldn’t try to tightly relate properties of transport media and related protocols (serial and parallel) and how they are accessed. Serial and parallel protocols are sequential: you send one (serial) or n (parallel) bits at a time. But that doesn’t determine the way the data you’re interested in is accessed at the application level — you can implement random or sequential access over any transport medium. – Stephen Kitt Oct 05 '18 at 07:42