B&R Industries Provit 5000, User Manual

Page: 146 / 400

Provit 5000 User’s Manual 145
Chapt
er
2
C
on
tro
lle
rs
Controllers • Lifespan of Silicon Disks (Compact Flash, PC Card)
12. Lifespan of Silicon Disks (Compact Flash, PC Card)
12.1 General Information
The silicon disks used in the IPCs are from SanDisk. They are 100% compatible with all
operating systems because of their ATA industry standard design.
12.2 Construction
A silicon disk is divided internally into individual sectors, whereby one sector corresponds to 512
bytes. (Example: 48 MByte = 48 * 1,024,000 Byte
1)
= 49,152,000 Byte / 512 Byte = 96,000
sectors ) These e.g. 96,000 sectors, are named "user sectors" and can be freely chosen by the
user.
Compact Flash and PC cards possess over 1% of spare sectors. Additionally they possess user
sectors, which are also based on their memory capacity. In the example, this corresponds to 960
spare sectors.
This additional memory is run automatically and therefore cannot be accessed by the user. The
necessity for these sectors is due to the limited number of write/erase cycles per sector, currently
estimated to be at least 300,000 accesses (typically 1,000,000 accesses). If a user sector can
no longer be successfully written to and checked, it is automatically replaced with a spare sector.
12.3 Organization of Data in an Application
a) Ring buffer storage
With ring buffer storage, data is always saved on the same sectors, e.g. from an application that
always writes the same amount of data (file size does not change). The date and time
information is also updated for the designated sectors.
b) Continuous storage
With continuous storage, the data is continually saved at the end of the last defined sector
(continuous writing e.g. trending). Date, time and file size information (changed with every write
cycle) is thereby updated for the designated sectors.
1) SanDisk use the following conversion formulas: 1 sector = 512 bytes, 1 MByte = 1,024,000 bytes