Relative speeds of different Types of Storage Media

Speed : Speed of computer storage devices is measured in the form of 'X'. Here, 1 X is a speed of 150 KiloBytes per second. Since the difference between taking a kilo as 1024 or 1000 doesnt make much difference, this has not been considered and compilations from sites that use both these kind of ratings are shown. Whenever the capital B is used to describe speeds, most people generally use it for bytes, and 'b' for bits. The 'X' rating is used for all peripherals below to give a comparative understanding of their speeds, though most speeds below are not measured in such terms.

Floppy Drives : The age old 3.5" floppy drives are still used to run boot disks or to transfer very small files. Most of these drives would give equal performances. They perform at average speeds of 0.2X practically.

Memory Sticks : Sony makes MS in purple and white colors, and white can be used along with copy-protected music under the SDMI initiative. These are compatible with all Memory Stick Compatible products except Sony's own MS Walkman.
Available in 4MB, 8MB, 16MB, 32MB and 64 MB. 128 MB sticks exist but are generally not available in India.
Specs : Flash Memory Type Universal Media, 10-Pin Connector, Can be used tens of thousands of times.\
These are very small in size. One can buy USB/PCCard/Floppy adaptors to use them with computers.
Sony specifies maximum speeds as : 2.0MB/s (writing), 2.45MB/s (reading).

Compact Flash (CF) cards : These cards generally are used with high-end digital cameras. Lots of these are available in the US. They come in sizes from 128 MB to 3 GB. A firewire card reader is the fastest way to read/write data with compact-flash cards. Cams are somewhat slower in accessing data from these cards. Practical maximum (card reader) average read speed for these cards are about 24X and write speeds are about 15X according to independant test results.

CD-ROM and DVD Drives : The X ratings on a DVD drive are not the same as those for the CDROM's.DVD 1x = CD 8X. DVD 3X = CD 24X, and DVD 5X = CD 32X. CD-Roms rotate at speeds of about 7200 RPM in the drive. Your actual (practical) maximum read speeds would be less than half the speed rating that the drive has. So, CD's would be read at practical maximum speeds of 12X to 30X for 24X to 60X rated CDRoms.
An Advice:
The lack of DMA bus-mastering forces the drive to work in PIO mode which not only hurts performance but also increases CPU utilisation. Check that the controller drivers are installed and that DMA is enabled for the channel and the drive itself.

LAN : The most popular LAN specifications are 100BaseTX and 10BaseT FullDuplex Ethernet based on PCI or onboard NIC's. Nowadays, Gigabit Ethernet as emerged as a new standard that allows a maximum theoretical bandwidth of 1Gigabit/Sec. A 10 MbPS (10BaseT) has a practical maximum speed of about 7.5X, 100 MbPS about ten times that, and Gigabit Ethernet, about 10 times the 100BaseTX. Practical average speeds got are about half of the above mentioned speeds in all 3 cases.

Hard Disks : The ATA mode, cache, and RPM rating, along with the file system are the most important factors in deciding the speed of a harddisk. Considering normal desktop internal harddisks, they come in capacities of 40 GB to 200 GB. ATA 33 is the slowest followed by ATA 66 and then the ATA 100, among the most used drives. Lots of other interfaces like USB, Firewire, SATA etc. are available but are not used since they are much costlier than their parallel ATA counterparts. Most harddisks available today run at 5400 RPM or 7200 RPM.They have practical maximum averaged (buffered, sequential & random , read and write ) speeds of about 67X to 210X.

RAM : Most RAM available today is either DIMM based SDRAM or DIMM based DDR SDRAM.
SDRAM's maybe classified into CL2 RAM and CL3 RAM, the digit indicating the number of clock cycles for which the processor must wait to get information from the RAM. SDRAM maybe classified by the Memory Bus speed. SDRAM is now available in bus speeds of 100 MHz and 133 MHz. Maximum theoretical memory bandwidth is got by multiplying the bus speed by 8 for SDRAM's. For example, for a 100 Mhz SDRAM, it would be 800 MB/sec. They have maximum practical speeds from 2,700X to 6,800X.

DDR SDRAM's can transmit data on both cycles of a clock pulse. DDR's are available in speeds of 266 MHz, 333 MHz, and 400 Mhz. From this, their maximum theoretical memory bandwidth can be calculated like for SDR's (by multiplying by 8). So they have theoretical maximum transfer speeds (or bandwidth) of 3200 MB/sec. Nowadays, all RAM chips perform equally well with integer data as well as floating point data. DDR's have max. practical speeds of 7,500X to 22,000X.

RD RAM is a standard that was float by Intel. This RAM is costly and was the fastest RAM even used in any desktop PC. Intel has now gone officially in favour of DDR RAM.

Cache : This is perhaps the fastest memory used inside a Desktop PC. Huge cache speed variations can be seen between different processors for small blocks (2 KB) whereas for blocks 64 MB and above the difference is negligible. Their practical max. speeds would be 70,000X to more than 2,00,000X (for 2 KB blocks).

Abhijit Pai

Sources :
Sisoft Sandra Professional 2003
www.dpreview.com
sonyindia.co.in