Member Avatar for mahela007

I was just reading about the different types of cables used to connect components of computers. When it comes to serial ports and parallel ports, parallel ports are faster because they send several bits of data simultaneously. Therefore, it should follow that parallel ATA is faster than Serial ATA. However, that's not the case. Why is this?

  • 4 Contributors
  • 7 Replies
  • 513 Views
  • 1 Day Discussion Span
  • Latest Post Latest Post by jbennet

Dani AI

Generated

Short answer: the engineering trade-offs that make parallel attractive in theory (many bits at once) become a liability at high speeds. Parallel links need every conductor to switch in lockstep, and tiny differences in trace length, capacitance and routing force huge timing margins as clock rates rise. Serial links avoid that by sending one high-speed stream that receivers can re-time and correct, so the per-wire bit rate can be pushed much higher.

Building on points from about cable and connector design, two practical advantages make serial interfaces like SATA faster in real use:

  • Parallel buses often force multiple devices to share one bus and carry extra protocol overhead for master/slave selection; point-to-point serial links give each drive a dedicated channel and remove that arbitration cost.
  • Modern serial links use on-chip electronics (clock recovery, equalization and framing) to tolerate channel imperfections and recover data reliably at much higher bit rates, so a single thin cable can carry more useful data than many parallel traces that must be kept perfectly matched.

A few pragmatic notes: sustained transfer rates on spinning disks are still limited by mechanics (seek time, rotation speed), so the interface often isn’t the bottleneck for older hard drives. For newer flash devices, interface design and protocol efficiency matter more — which is why storage has continued to move toward high-speed serial interfaces. To compare real-world performance, run sequential and random I/O benchmarks and verify the controller and OS are using the fastest transfer mode supported by the drive.

Recommended Answers

All 7 Replies

Member Avatar for jbennet

Its more extensible. Most of the wires in an old style ATA connector dont actually help transmit data, they are to stop interference (they actualy doubled the number of wires to 80 by adding more grounds). SATA however, has a higher cieling for this so just uses two pairs of wires for a total of 4 (with 3 grounds). This means its got a reduced cost and is easier to route as its smaller and allows for 3-6gb speeds under the current commn SATA specs. SATA also uses twisted pairs and differential signalling (sending the inverse of each signal to compliment eachother and reduce interference in much the same way as noise cancelling headphones do) which reduce interference and keep data rates up.

SCSI is technically faster, but its more expensive to implement due to its architechture.

Edited by jbennet because: n/a
commented: Was searching for this reason since long. Found a thread. Nice reply !! +0
Member Avatar for mahela007

Isn't SCSI deprecated?

Member Avatar for zortec

No, it is not deprecated yet but it will be soon now that SATA-2 has taken over.

Member Avatar for jbennet

No, it is not deprecated yet but it will be soon now that SATA-2 has taken over.

No, it will be superceded by SAS if anything.

Member Avatar for Member #585571

Its more extensible. Most of the wires in an old style ATA connector dont actually help transmit data, they are to stop interference (they actualy doubled the number of wires to 80 by adding more grounds). SATA however, has a higher cieling for this so just uses two pairs of wires for a total of 4 (with 3 grounds). This means its got a reduced cost and is easier to route as its smaller and allows for 3-6gb speeds under the current commn SATA specs. SATA also uses twisted pairs and differential signalling (sending the inverse of each signal to compliment eachother and reduce interference in much the same way as noise cancelling headphones do) which reduce interference and keep data rates up.

SCSI is technically faster, but its more expensive to implement due to its architechture.

Thanks for this great info.

Edited by Member #585571 because: n/a
Member Avatar for mahela007

yes.. Thanks for the gread info but I don't think you answered my original question.
Why is SATA faster? (Every bit has to be sent one behind the other)

Member Avatar for jbennet

yes.. Thanks for the gread info but I don't think you answered my original question.
Why is SATA faster? (Every bit has to be sent one behind the other)

Because there is less electrical interference when you send things in serial fast in one direction at a time over a lower set of wires than when you send things in parallel over more wires (as in the case with PATA). PATA should in theory be faster but it isn't due to this limitation.

Its just like with network cables. To achieve gigabit speeds the cables have much more shielding to prevent crosstalk (which reduces bandwidth)

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.