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Why is SATA simplex even though it has separate TX+/- and RX+/- pairs? Why can't it be full-duplex like SAS (which has the same interface with multiple ports and is full-duplex). If I am wrong with this concept please correct me.

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  • \$\begingroup\$ Unsure if this question is on topic here. \$\endgroup\$
    – jippie
    Aug 16, 2013 at 6:09

2 Answers 2

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For backward compatibility with PATA/ATA/ISA, SATA uses the PATA/ATA/ISA command set. PATA/ATA/ISA is simplex because it is a connector to the ATA/ISA/PC/XT bus which is simplex. The ATA/ISA/PC/XT bus was simplex because it was a connector to the 8086/8088/80286 processor data bus, which was simplex.

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SATA is consumer grade electronics it must come cheap with huge capacity. SAS is enterprise grade electronics, they care about speed, reliability and much less about money. Check the price and capacity difference for SATA and SAS drives. So my guess is price to build it.

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    \$\begingroup\$ @Jipple:SATA ans SAS have same interface details. SAS can be expanded with multiple ports. When you have interface for full-duplex, why can't use it. \$\endgroup\$
    – user19579
    Aug 16, 2013 at 7:56
  • \$\begingroup\$ That's what I'm saying, because the actual hardware implementation costs extra money and consumer market has very low margins. If in theory a SAS drive would be $1 more expensive than a SATA disk, guess which one will be sold. \$\endgroup\$
    – jippie
    Aug 16, 2013 at 15:20
  • \$\begingroup\$ @jippie No, it's not because they're cheap -- it's more likely because full-duplex SATA wouldn't only mean improved performance for existing SATA users, it would also potentially steal sales away from SAS disks and hardware. The reduced differentiation would also mean some people buying SATA hardware not understanding the differences, and potentially upset if the performance and reliability don't meet SAS standards. Better to have folks upset at the cost than upset at the quality or performance. \$\endgroup\$
    – apraetor
    Feb 18 at 2:06

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