Compare AHCI and IDE

The vast major­i­ty of mod­ern hard dri­ves involve con­nect­ing to a com­put­er via the SATA inter­face. It pro­vides a high data trans­fer rate while main­tain­ing the reli­a­bil­i­ty of this very infor­ma­tion (that is, it is exchanged quick­ly and with­out errors).

How­ev­er, SATA is a phys­i­cal inter­face. That is just a cable and two con­nec­tors. At the soft­ware lev­el, even such a term as SATA does not exist. Instead, AHCI is used. How­ev­er, SATA hard dri­ves are capa­ble of emu­lat­ing IDE, an old ver­sion of the inter­face for exchang­ing infor­ma­tion. And it is con­fig­ured direct­ly through the BIOS.

And so a fair ques­tion aris­es — which inter­face to choose after all? In this arti­cle, we will ana­lyze what is the dif­fer­ence between AHCI and IDE — and which is bet­ter to use.

AHCI Mode

AHCI mode (Advanced Host Con­troller Inter­face) — “native” for the SATA inter­face. It was designed specif­i­cal­ly to achieve all the advan­tages of this con­nec­tion method. And the most impor­tant of them are two — “hot plug” and sup­port for NCQ.

“Hot plug” implies the nor­mal oper­a­tion of the “hard dri­ve” when it is con­nect­ed to an already turned on and run­ning com­put­er. In prin­ci­ple, for most users, such an oper­a­tion is some­thing out of the ordi­nary. How­ev­er, in some cas­es it is impor­tant:

1. For exam­ple, if the sec­ond “hard dri­ve” is installed instead of a SATA dri­ve. After all, it’s the 21st cen­tu­ry out­side the win­dow, and all sorts of CDs and DVDs are used once in a while. It is much more expe­di­ent to install a spe­cial sled instead of a dri­ve and stick an addi­tion­al dri­ve into them;

2. Or when it comes to serv­er sys­tems where a quick change of data­base or file stor­age is required. To do this, you do not need to turn off the “machine”, just pull out one HDD array and plug in anoth­er;

3. Or you need to con­nect some kind of “hard dri­ve” to check its per­for­mance or “save” infor­ma­tion if the com­put­er breaks down.

NCQ (Native Com­mand Queu­ing, “Native Com­mand Queu­ing”) is a spe­cial tech­nol­o­gy that redis­trib­utes the sequence of read and write com­mands com­ing to the “hard dri­ve” to improve per­for­mance. It is most pro­nounced on the HDD.

The fact is that mag­net­ic hard disks (HDD) imply the stor­age of infor­ma­tion on tracks. Like gramo­phone records, only much faster and more pro­duc­tive. And the speed of read­ing / writ­ing with ran­dom access to files is deter­mined by the dis­tance between the tracks.

NCQ redis­trib­utes the read/write com­mand queue so that they are more or less sequen­tial. This speeds up access to infor­ma­tion.

Of course, when using SSDs (Sol­id State Dri­ves), NCQ is not real­ly need­ed. But these same dri­ves are still too expen­sive and are not found in all com­put­ers. And with tra­di­tion­al HDDs, NCQ tech­nol­o­gy can sig­nif­i­cant­ly speed up the load­ing of the oper­at­ing sys­tem and increase per­for­mance when per­form­ing resource-inten­sive oper­a­tions.

By the way, SSD dri­ves only work in AHCI mode.

How­ev­er, AHCI is a fair­ly new tech­nol­o­gy. There­fore, old­er oper­at­ing sys­tems like Win­dows XP or the first ver­sions of Ubun­tu sim­ply do not sup­port it. Of course, you can install AHCI sup­port dri­vers, but before that you need to some­how install the OS itself.

So, let’s sum up.

IDE Mode

IDE mode emu­lates the PATA (IDE) con­nec­tion in SATA hard dri­ves to ensure com­pat­i­bil­i­ty with lega­cy soft­ware such as the Win­dows XP oper­at­ing sys­tem or even old­er.

Actu­al­ly, IDE mode is not required for any­thing else. It does not pro­vide hot plug­ging or any per­for­mance enhance­ment tech­nolo­gies. The only task of the IDE mode when con­nect­ing an HDD via a SATA cable is to ensure the com­pat­i­bil­i­ty of old soft­ware and new tech­no­log­i­cal solu­tions.

The choice of the oper­at­ing mode of the hard disk goes direct­ly to the BIOS. At the same time, if the oper­at­ing sys­tem was installed in AHCI mode, and then some­one switched it to IDE, the com­put­er will not boot at best. At worst, a blue screen of death will appear.

So, let’s sum up.

More­over, the above speed is the­o­ret­i­cal. In prac­tice, it turns out to be much less, since exter­nal con­nect­ed devices “take away” it. “Win­ches­ter” is placed on the same bus as oth­er devices — name­ly PCI with a fre­quen­cy of 22 MHz. There­fore, at home, achiev­ing a speed of 133 megabytes per sec­ond sim­ply will not work.

The task of the IDE mode is to ensure the com­pat­i­bil­i­ty of the “new” “hard­ware” and the “old” “soft­ware”. And no more.

Which is better — AHCI or IDE?

If you have a SATA hard dri­ve and you plan to install a new oper­at­ing sys­tem on your com­put­er — for exam­ple, Win­dows 7 or Win­dows 10 — then, of course, it is bet­ter to select the AHCI mode. The IDE is slow and is need­ed for hard­ware com­pat­i­bil­i­ty with Win­dows 10 and the first ver­sions of Lin­ux-like sys­tems.

Now let’s com­pare these two modes of oper­a­tion.

Impor­tant! If you have an SSD, then there is not much choice. It is only sup­port­ed by AHCI SATA.

By the way, if you need to con­nect a new hard dri­ve to an old moth­er­board — or vice ver­sa — then you can not switch to IDE mode, but use a spe­cial SATA-PATA adapter. They exist and are not that expen­sive.

There is an impor­tant aspect. If the oper­at­ing sys­tem was installed in the AHCI state, then it should con­tin­ue to work in it. It is not rec­om­mend­ed to switch any­thing in the BIOS on your own. After chang­ing the pro­to­col, the oper­at­ing sys­tem may refuse to boot or start to work inad­e­quate­ly — with “brakes”, errors and incor­rect access to the HDD. For exam­ple, one of the sec­tions may sim­ply “dis­ap­pear”. The same is true for the IDE.

By switch­ing to the AHCI pro­to­col and then rein­stalling the oper­at­ing sys­tem, you can improve the over­all per­for­mance of your com­put­er by an aver­age of 20%. And this is true for rel­a­tive­ly old com­put­ers that are equipped with Ser­i­al ATA 1.0. The new “machines” that have received the next gen­er­a­tion of inter­faces offer an even greater increase in per­for­mance. But the spe­cif­ic val­ue depends pri­mar­i­ly on the “hard dri­ve” itself. For exam­ple, WD Blue pro­vides an increase of about 25%, and WD Green — about 17%.

In gen­er­al, it’s bet­ter not to “dig” in the BIOS set­tings once again. Inept changes in para­me­ters can lead to loss of infor­ma­tion and the need to rein­stall Win­dows.