IDE vs. SCSI
The Main Hard Drive Interfaces
The computer market is dominated by two main hard drive interface standards today -- IDE/ATA and SCSI . Which is better is still debated endlessly on the Internet and in the technical community. The simple answer is that neither is really better than the other - it depends on how you plan to use your hard drive. This can be deduced by the market. If one hard drive interface were clearly superior to the other in every way, the superior one would have taken over the market completely. The fact that both are in common use (and have been for many years) proves that both have valid reasons for being used in mass. Contrast this to the older MFM, RLL and ESDI hard drive interfaces, for example, which were made obsolete by IDE/ATA since they virtually had no advantages to allow them to continue.
Whether IDE/ATA or SCSI is better depends on how you will be using your hard drive, and how much you are willing to spend. To gain an overall look at the two hard drive interfaces, we will look at various performance and quality aspects of the interfaces and see how IDE/ATA and SCSI compare.
IDE vs SCSI: Number of Drives to be Used
The primary factor in the SCSI vs. IDE/ATA hard drive interface question is the number of hard drives (or other devices which connect to the interface) you plan to use now, or in the future, in your system. In many respects, IDE/ATA is superior if you are using only one, two or three devices such as hard disks or CD-ROMs. If you are using many devices, say over four, then SCSI is superior to IDE/ATA in several different respects. It is worth mentioning that often people make the decision about what hard drive interface to use based on what they currently are using. Not many want to buy all new devices when making an interface switch. Please note it is possible to use both interfaces in the same computer system.
The popularity of the SCSI hard drive interface is increasing rapidly, but this could be due to a common misunderstanding. It is often thought that SCSI hard drives deliver much higher performance than IDE hard drives. While SCSI does produce a faster throughput, the way a person uses the computer system determines the level of performance which will be realized. There are a few factors which must be considered to determining which is better for you.
Performance Differences between
IDE Hard Drives and SCSI Hard Drives
Most personal computers today come with IDE hard drives because they are cheap and perform well. But, to get a full view of the hard drive performance, you need to look at the entire drive.
Many manufacturers release identical model hard drives in both IDE and SCSI formats. If you look at these drives closely, they are almost identical except for circuitry board (logic board) that controls them. This means that the HDA (head disk assembly) and other drive mechanics are the same. The difference is mainly in the logic board. The IDE logic board has the disk controller and the AT bus interface. The logic board on the SCSI drive contains one extra computer chip. Basically, this chip is a SCSI adapter to allow the drive to operate on a SCSI bus. So, structurally, the IDE hard drive and SCSI hard drives are the same.
With this information in mind, the performance overhead of SCSI over IDE comes mainly from structure of the bus, not the hard drive mechanicals. The nature of the SCSI bus allows it to perform better when doing data intensive tasks such as multi-tasking. The SCSI bus controller is capable of controlling the drives without any work by the processor. Also, all drives on a SCSI chain are cable of operating at the same time. With IDE, one is limited to only two drives in a chain, and these drives cannot work at the same time. They, in effect, must "take turns".
Comparison of IDE Hard Drives and SCSI Hard Drives
In some computers, SCSI is better. As mentioned above, SCSI is a more efficient bus than IDE. There are many steps in the SCSI data transfer, but Operating Systems that allow multitasking, or if you often use several programs at once, the SCSI drive is a better choice because this extra intelligence of the SCSI bus is used.
In addition, SCSI devices can communicate independently from the CPU over the SCSI bus. This is due to the fact that each device has its own embedded controller. Data can then be transferred at high-speeds between the devices without taking any CPU power. IDE uses controllers on each device, but they cannot operate at the same time and they do not support command queuing.
Summary of IDE Hard Drives vs. SCSI Hard Drives
It is probably safe to say that for most people, IDE is just fine and offers very good performance. The reason most people do not need to get SCSI is that most users do not use their system in a way that would actually justify the SCSI bus. While the nature of the bus is faster, it takes certain situations to actually need it. And finally but not least, the SCSI drives are more expensive.