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**Praetor** · 03-31-2005, 02:16 PM

CRC -- Cyclic Redundancy Checking, this is a basic error checking routine whereby a mathematical calculation (binary polynomial division and remainder is used as the verification unit) to determine if data was corrupted during transmission.

Native Command Queuing (NCQ) -- Configurations (both drives and controllers require support) supporting NCQ attempts to queue together a series of instructions and execute them in the most efficient manner possible (efficiency is with respect to the physical layer). As a quick example, suppose data is required from "location" 1000, 55000 and 1005; a non-NCQ drive processes requests literally, 1000->55000->1005 but a NCQ configuration will process it as 1000->1005->55000. The difference is that the time it takes for read-write heads to move from location 1000 to 1005 is miniscule however the transition to/from 5500 is significant. A single queue of operations may not yield impressive performance gains however hard drives are required to execute millions of such transactions and those gains are cumulative

Partitioning and Formatting -- Straight out of the box, a hard drive's file system is "raw" which is unusable. In order to bring the drive to a useable state, it must first be partitioned and then those partitions need to be formatted. Partitioning refers to the process of subdividing the available space on a HDD into logical units (thus making c, d, e etc "drives"). Formatting refers to converting the file system from "raw" to format recognized by the operating system such as FAT, NTFS or EXT2

Cache -- Hard drives are mechanical devices: no matter how much you improve the dynamics or increase the spindle speed, a mechanical transfer will always lose out (in terms of performance) to an electrical system. To alleviate/hide the slow nature of hard drives, they [the drives] are often equipped with a small amount of high-speed memory. When a request is received, the drive checks for a match in the cache before "manually" locating the data on the various platters: if there is a cache-hit (i.e., the data required is there) then the data can be immediately transferred thus eliminating seek times. Increasing the amount of cache available on the drive noticeably improves. Hard drives usually come with 2MB, 8MB or 16MB of cache. For some fancy RAID controllers, there is also cache memory present on the controller.

Spindle Speed aka Rotation Speed -- Measured in revolutions-per-minute this is literally the mechanical rotation speed of the disk platters. The faster the rotation, the sooner the drive heads can be positions underneath the desired location. Modern drives feature anywhere from 3600rpm to 15,000rpm.

[Average] Access Time -- A composite measure of the seek-time and rotational-latency, access time (measured in ms) is the sum total of the time it takes to move the disk head to the appropriate track on the platter (seek time) and the time it takes to move the appropriate sector (of the platter) underneath the drive head (rotational latency). Rotational latency can be reduced by increasing the spindle speed.

03-31-2005, 02:16 PM	#3 (permalink)
Praetor Administrator Join Date: Jul 2004 Location: Canada Age: 26 Posts: 19,953	Definitions Part 02 *CRC* -- Cyclic Redundancy Checking, this is a basic error checking routine whereby a mathematical calculation (binary polynomial division and remainder is used as the verification unit) to determine if data was corrupted during transmission. *Native Command Queuing (NCQ)* -- Configurations (both drives and controllers require support) supporting NCQ attempts to queue together a series of instructions and execute them in the most efficient manner possible (efficiency is with respect to the physical layer). As a quick example, suppose data is required from "location" 1000, 55000 and 1005; a non-NCQ drive processes requests literally, 1000->55000->1005 but a NCQ configuration will process it as 1000->1005->55000. The difference is that the time it takes for read-write heads to move from location 1000 to 1005 is miniscule however the transition to/from 5500 is significant. A single queue of operations may not yield impressive performance gains however hard drives are required to execute millions of such transactions and those gains are cumulative *Partitioning and Formatting* -- Straight out of the box, a hard drive's file system is "raw" which is unusable. In order to bring the drive to a useable state, it must first be partitioned and then those partitions need to be formatted. Partitioning refers to the process of subdividing the available space on a HDD into logical units (thus making c, d, e etc "drives"). Formatting refers to converting the file system from "raw" to format recognized by the operating system such as FAT, NTFS or EXT2 *Cache* -- Hard drives are mechanical devices: no matter how much you improve the dynamics or increase the spindle speed, a mechanical transfer will always lose out (in terms of performance) to an electrical system. To alleviate/hide the slow nature of hard drives, they [the drives] are often equipped with a small amount of high-speed memory. When a request is received, the drive checks for a match in the cache before "manually" locating the data on the various platters: if there is a cache-hit (i.e., the data required is there) then the data can be immediately transferred thus eliminating seek times. Increasing the amount of cache available on the drive noticeably improves. Hard drives usually come with 2MB, 8MB or 16MB of cache. For some fancy RAID controllers, there is also cache memory present on the controller. *Spindle Speed aka Rotation Speed* -- Measured in revolutions-per-minute this is literally the mechanical rotation speed of the disk platters. The faster the rotation, the sooner the drive heads can be positions underneath the desired location. Modern drives feature anywhere from 3600rpm to 15,000rpm. *[Average] Access Time* -- A composite measure of the seek-time and rotational-latency, access time (measured in ms) is the sum total of the time it takes to move the disk head to the appropriate track on the platter (seek time) and the time it takes to move the appropriate sector (of the platter) underneath the drive head (rotational latency). Rotational latency can be reduced by increasing the spindle speed. __________________ ASUS P5K Premium WiFi-AP, Q6600@3.7 / ASUS P5ND, E6400@3.8 4GB OCz Platinum XTC 8500 / 4GB CorsairXMS2 6400 5x500GB Seagate 7200.10 / 2x500 Seagate 7200.10 OCz 8800GTX 768MB @ 630/800 / 2x Galaxy 8800GT SLI Last edited by Praetor; 03-31-2005 at 02:18 PM.