Sunday, October 28, 2012
Friday, March 30, 2012
Here are the high-level differences between SAS and SATA disk drives:
- SATA disk drives are the largest on the market. The largest SATA drives available with widespread distribution today are 1.5TB-2TB.
- SAS disk drives are typically smaller than SATA. The largest SAS drives available with widespread distribution today are 450GB.
- So, for capacity, a SATA disk drive is 3X-4x as dense for capacity than SAS.
- A good way to quantify capacity comparison is $/GB. SATA will have best $/GB.
- SATA disk drives spin at 7.2k RPMs. Average seek time on SATA is 9.5msec. Raw Disk IOPS (IOs per second) are 106.
- SAS disk drives spin at 15k RPMs. Average seek time on SATA is 3.5msec. Raw Disk IOPS (IOs per second) are 294.
- So, for performance, a SAS hard drive is nearly 3X as fast as SATA.
- A good way to quantify performance comparison is $/IOP. SAS will have best $/IOP.
Reliability: there are two reliability measures – MTBF and BER.
- MTBF is mean time between failures. MTBF is a statistical measure of drive reliability.
- BER is Bit Error Rate. BER is a measure of read error rates for disk drives.
- SATA drives have a MTBF of 1.2 million hours. SAS drives have a MTBF of 1.6 million hours. SAS drives are more reliable than SATA when looking at MTBF.
- SATA drives have a BER of 1 read error in 10^15 bits read. SAS drives have a BER of 1 read error in 10^16 bits read. SAS drives are 10x more reliable for read errors. Keep in mind a read error is data loss without other mechanisms (RAID or Network RAID) in place to recover the data.
Monday, February 20, 2012
ICC - Integrated Circuit Card (aka smart card)
IFD - Interface Device (aka smart card reader)
There are variety standards or methods for such. Among others are ISO 7816-4, EN 1546, and Unilateral Authentication. The following table displays an example of mutual authentication according to ISO 7816-4 standards.
| || |
A figure XIFD is sent to ICC to decrypt. XIFD is the encryption of Master Key KIFD which is the combination of seed keys from both IFD and ICC (RNDIFD and RNDICC ).
XIFD will be decrypted at ICC to obtain the value of Master Key KICC , which will then revealed the calculated seed keys (RND’IFD and RND’ICC ).
| || |
RND’ICC = RNDICC ?
The calculated value RND’ICC is compared with RNDICC . If seed keys matched, ICC regards IFD as a trusted source.
| || |
A figure XICC is sent to IFD to decrypt. XICC is the encryption of Master Key KICC which is the combination of seed keys from ICC (RNDICC) and calculated seed key of IFD (RND’IFD). This time, the arrangement of the seed keys has been reversed.
| || |
XICC will be decrypted at IFD to obtain the value of Master Key KIFD , which will then revealed the calculated seed keys
(RND’ICC and RND’IFD ).
RNDIFD = RND’IFD ?
| || |
The calculated value RND’IFD is compared with RNDIFD. If seed keys matched, IFD regards ICC as a trusted source.
Thursday, November 24, 2011
Direct-to-Card (DTC®) printing is the most common technology used by desktop card printer/encoders to transfer images directly onto a plastic ID card. DTC technology prints images by heating a print ribbon beneath a thermal printhead, resulting in the transfer of color from the ribbon to a blank card.
Sharp edges, deep blacks and the full spectrum of colors
DTC technology uses two printing methods to achieve its incredible image quality:
Dye-sublimation prints smooth, continuous-tone images that look truly photographic. A dye-based ribbon is partitioned by multiple color panels, which are grouped in a repeating series of colors along the ribbon’s length.
A printhead containing hundreds of thermal elements heats the dyes, which vaporize and diffuse into the card surface. By combining colors and varying the heat used to transfer them, dye-sublimation is capable of producing up to 16.7 million colors.
Resin thermal transfer uses a single-color ribbon to print sharp black text and crisp bar codes, which can be read by both infrared and visible-light scanners. While this process uses the same thermal printhead as dye-sublimation, solid dots of color are transferred rather than a combination of colors.
Source: Fargo Website
Thermal transfer printing and dye sublimation printing are used in both direct to card printers and retransfer printers. Direct to card printers merge the image directly on the surface of the card. Retransfer printing deposits the image on the back of a clear plastic film. This film is then bonded to the surface of a plastic card. Retransfer printing is the newest of these printing types and results in a better image result. The card design is applied to specialized cards and does not require a perfectly smooth card as the direct to card printers require.
Thermal Transfer Printing
Thermal printing is when resin or ink is melted off of a printer ribbon and is directly transferred to the retransfer film or the surface of the card. To melt the ink,a print head is used. The print head has heated pins that are aligned across a ceramic plate. In the correct sequence,the pins in the print head receive instructions to heat and release ink at just the right moment. The desired digital image created in the software is recreated on the card or ribbon.
Colored prints require the use of Y,M and C panels. As each panel passes over the card,dots of color are released resulting in the completed image. The K panel produces needed black printing on the card. Dithering allows the dots of different colors to be placed close together to create a blended shade when observed.
Monochrome printing is also available. This single color ribbon produces clear results with standard text and with bar codes. Monochrome printing is completed at high speeds and is often used to customize a preprinted card. The thermal ribbons provide durable print that resists fading. The resin dries quickly.
Sublimation is when a solid is heated directly into a gaseous state. The solid bypasses the liquid state during heating. With this printing,the dye is heated to about 250 degrees Fahrenheit while the polymers in the PVC card are heated to 350 degrees. The gaseous dye penetrates the plastic and as the card cools,the dye chemically bonds with the plastic card.
Crisp,sharp images are printed with dye sublimation printing. Photographic images are printed with accuracy. The higher heat levels allow more dye to be released into the card surface. The result is the colors blend into a pleasing result as there is control over the opacity and transparency of the printing result.
Colors in this printing method are applied one panel at a time- the Y,M and C. This type of print is prone to fading when exposed to UV rays from the sun. Often a UV resistant topcoat is recommended to help protect the dye printed cards.